Organic Vegetable Gardening - PB 1391
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Agricultural Extension Service
The University of Tennessee
PB 1391
Organic Vegetable
Gardeningblank page
TableofContents
I. What is Organic Gardening? 4
A. Organic Gardening and Pesticides 4
B. Organic Gardening and Fertilization 4
II. Why Garden Organically? 4
A. Quality 4
1. Nutrition 4
2. Taste 4
3. Pest Damage 4
4. Residues 4
B. Soils 4
C. Psychological Effect 5
III. Limitations of Organic Gardening 5
A. Lack of Organic Alternatives 5
B. Climatic Effect (geographic and
annual) 5
C. Population Cycles 5
D. Inability to Tolerate Damage 5
E. Cost of Produce 5
F. Sources of Nutrients and Organic
Matter 5
IV. Alternative Means of Pest Control 5
A. Choose Vegetables and Varieties Wisely 5
B. Grow Resistant Varieties 6
C. Grow Hybrid Varieties 6
D. Obtain Quality Seed and Transplants 6
E. Use Cultural Controls 6
F. Eliminate Plant Debris 7
G. Increase Soil Organic Matter 7
H. Rotate Plant Families 7
I. Avoid Stress 8
J. Try Companion Planting 8
K. Use Intercropping 8
L. Time Plantings Carefully 8
M. Time Irrigation Properly 8
N. Provide Air Circulation 9
O. Use Mulches 9
P. Consider Using Solarization 9
Q. Avoid Introducing Pest Problems 10
R. Use Plant Supports 10
2V. Other Alternative Means of Pest Control 10
A. Barriers 10
B. Repellents 12
C. Traps 12
D. Baits 12
E. Birds 12
F. Beneficial Insects 13
G. Handpicking 13
VI. Protective Chemicals 14
VII. Natural Protective Substances 14
A. Water 14
B. Bug Juice 14
C. Hot Pepper 15
D. Soaps 15
E. Oils 15
F. Microbial Agents 15
G. Sulfur 15
H. Copper 15
I. Other Protective Chemicals 15
J. Botanically-Derived Chemicals 16
VIII. Managing Soil Organically 16
A. Introduction 16
B. Maintaining or Increasing Soil Organic Matter 16
C. Using Crop Residues 17
D. Crop Rotation 17
E. Green-Manure Cover Crops 17
F. The Effect of Mulches on Soils 18
G. Making and Using Compost 19
IX. Using Lime and Organic Fertilizers 20
A. Increasing Soil pH 20
B. Adding Nutrients — Manure 20
C. Adding Nutrients — Non-manure 21
D. Soil Amendments 22
X. References 22
3OrganicVegetableGardening
David W. Sams, Professor, Plant & Soil Science
Darrell D. Hensley, Assistant Extension Specialist, Entomology & Plant Pathology
nutritional quality or better taste; however, there is no
What is Organic Gardening? evidence to support this. Since plants take up nutri-
There is considerable discussion, even among ents dissolved in water as ions, and ions from all
those claiming to be organic gardeners, as to exactly fertilizer sources are identical, there is no reason to
what constitutes organic gardening. Generally, suspect taste or nutritional differences directly
however, organic gardening is a system of gardening because of nutrient source. Organic fertilization can,
that attempts to use only sustainable, ecologically however, affect soil organic matter content, structure,
sound gardening procedures. Organic gardening moisture retention and nutrient release. Some of these
generally differs from traditional gardening in two may affect plant vigor, cell size or content, thereby
important ways: use of agricultural chemicals and use indirectly affecting nutritional quality or taste. Very
of artificial or processed fertilizers. possibly, any effect on nutritional quality or taste is
Commercially, organic growers in Tennessee are the result of organically grown vegetables being
certified by the Tennessee Land Stewardship Associa- locally grown and thus fresher. Both nutrient content
tion. There are currently three levels of certification. and taste are generally at a maximum at harvest and
More information may be obtained from T.L.S.A., decline thereafter.
P.O. Box 328, Bell Buckle, TN 37020 Many people garden organically partially because
of concern over pesticide residues on food, or in soil
Organic Gardening and Pesticides or groundwater. However, careful use of pesticides
Organic gardening rejects the use of all artificial according to their labeled instructions need not leave
agricultural chemicals, including pesticides used to residues in soils or groundwater. Furthermore, the
control insects, diseases, weeds and nematodes, as residues found in food are generally believed to be
well as other agricultural chemicals used to affect much higher than they really are. One should also
physiological processes and conditions such as remember that residue tolerances for food are gener-
flowering, fruit color and firmness. Organic gardeners ally set at only 1/100 of the amount thought to be
differ concerning which, if any, naturally derived harmful.
pesticides are permissible and when and how they A discussion of the effect of organic gardening on
may be used. Recent trends have been toward using food quality should not end without mention of insect
fewer pest control agents in organic gardening, and disease damage. Organic gardeners are generally
regardless of their origin. willing to tolerate some damage that traditional
agriculture perceives as reduced quality. Organic
Organic Gardening and Fertilization gardeners generally feel occasional insect or disease
Most organic gardeners consider soils to be a injury or reduced color and shelf stability are worth
living, biotic system and reject artificial chemical the environmental benefits of growing vegetables
fertilizers as too harsh to be applied to living soils. organically.
Organic gardeners emphasize building soil organic
matter and then rely on natural sources of supplemen- Effect on Soils
tal nutrients. There is little doubt that organic gardening
improves soils because of the emphasis on increasing
Why Garden Organically? soil organic matter. Increased soil organic matter
improves soil tilth and structure, improves water
Quality
retention, evens out nutrient release and may reduce
Organic gardeners generally feel that organically
erosion and run off. It should be pointed out, how-
grown food is superior to non-organically grown food
ever, that the heavy applications of manure sometimes
with respect to one or more components of quality.
used by organic gardeners can create their own run-
Some would argue that organic food has higher
off problems.
4Psychological Effect Inability to Tolerate Damage
A final reason for organic gardening, and perhaps Many organic control methods rely on maintain-
one of the best reasons, is that it helps some people ing an equilibrium between pest and host. This means
feel safer. When gardening organically, they no longer the organic gardener frequently must be willing to
worry about damaging their environment or family tolerate some damage. How much damage will be
with chemicals. There seems to be little harm in this, tolerated depends on the individual and also on
as long as gardeners realize that even organic prod- whether or not any produce is to be sold. Consumers
ucts must be used as they are designed and labeled to frequently complain if even a single insect or fraction
be used and can be harmful if misused. of an insect is found, and lawsuits are not unknown.
LimitationsofOrganicGardening Cost of Organically-Grown Vegetables
It would seem, at first, that not using agricultural
Lack of Organic Alternatives chemicals or commercial fertilizers would reduce the
Some pest problems are easily controlled by cost of organically grown vegetables. This is seldom
organic alternatives. Others are controlled only with the case. Organic vegetables are often more expensive
difficulty or have no reliable organic controls. Some than traditionally grown vegetables for several
crops either must be avoided by organic gardeners or reasons.
these gardeners must be willing to risk significant First, organic sources of nutrients or organic pest
losses from pests. control measures are often more expensive than
traditional sources. Second, marketable yields are
Climatic Effect frequently less with organic production. Lastly,
Climate varies regionally and annually. A pest organic produce may not store or ship as well as
may pose little or no problem in one climate but be a traditional produce.
severe problem in another. Aphids, for example,
require high humidity to shed their skins and are not a Sources of Nutrients and Organic Matter
severe problem in regions of low humidity. They are,
Organic production frequently relies, at least
however, a severe problem in Tennessee and much of
partially, on manure, organic material and nutrients
the humid Southeastern United States.
brought in from outside the growing area. These
Even within a single state, climatic factors vary
resources are limited and may restrict the expansion
with altitude, nearness to bodies of water, slope of the
of organically-grown vegetables. Increased use of
land, etc. These differences also affect plant suscepti-
cover crops, green manure crops, crop rotation, etc.
bility to problems and limit the effectiveness of
can minimize the effect of the limitations of natural
organic controls as well as chemical controls.
resources.
There are also annual climatic differences which
Despite the limitations of organic gardening, there
affect host and pest. An organic control measure that
are many proven techniques that will reduce the need
works well one year may not work well the following
for artificial pesticides and improve soils without
year because of this climatic variation.
artificial fertilizers. We will now examine some of
these.
Population Cycles
Natural populations tend to expand until they are
limited by their food supply or by another organism. AlternativeMeansofPestControl
An insect species, for example, may have only Choose Vegetables and Varieties Wisely
scattered individuals in an area, but have ample food. A few vegetables can frequently be grown
Its numbers increase rapidly for a few years and it without serious damage from insects and diseases.
becomes abundant. It then either consumes most of Examples include beets, carrots, garlic, okra, onions,
the available food or becomes infested by a disease radishes and many herbs. Many other vegetables are
organism and most individuals die. The remaining susceptible to frequent attack by a number of insect or
scattered population then begins a new cycle. The disease organisms.
significance of this for organic gardeners is that a pest
may be much more severe in one year than in another.
It is difficult to determine how well an organic control
is working because of these natural population cycles.
5Grow Resistant Varieties are much less common. Also, obviously diseased or
The University of Tennessee Agricultural Exten- off-type plants are rogued out before they produce
sion Service factsheet SP277-K, “Disease Resistance seed. These seed are also packed and stored properly,
in Recommended Vegetable Varieties for Home so they will germinate well.
Gardens,” lists more than 50 varieties of 21 veg- Inspect transplants for the presence of insects,
etables reported as resistant to one or more diseases. leaf spots or yellowing and dying leaves. Never
Many of these varieties have resistance to three or purchase transplants showing signs of insect infesta-
more diseases. It is important to remember that tion or diseases. Young, vigorously growing trans-
resistance is not immunity. A resistant variety will plants in individual cells of a cell pack are likely to
probably not totally escape a pest, but may be at- grow most vigorously; bare-root and older plants,
tacked later or bear a fair crop despite being attacked least vigorously. Inspect the roots of bare-root plants
by the pest. Selecting vegetable varieties resistant to and do not buy them if the roots have dried and died.
several pests is well worthwhile if you desire to
reduce the use of plant protective chemicals. Use Cultural Controls
A wide range of cultural techniques can be used
Grow Hybrid Varieties to reduce problems of home gardens. Methods of
Hybrid varieties are often more pest resistant than control vary considerably from one pest to another,
non-hybrid varieties. This is because hybrids are depending on the kind of pest, the vegetable affected
crosses of true breeding lines. They are frequently and the interaction of the two. The damage or loss of
selected to contain specific pest resistance from both one or a few plants is usually considered insignificant.
parent lines. Hybrids also tend to be high-yielding, Control measures are generally aimed at saving the
earlier-bearing and longer-living than non-hybrid majority of the crop rather than individual plants.
vegetables, when grown under favorable conditions. Most control measures aim at helping plants avoid
Their increased vigor may permit them to tolerate or contact with pests, as well as eradicating or reducing
outgrow a minor attack. the numbers of pests in the area. These methods
Unfortunately, many organic gardeners prefer include sanitation, proper row spacing, varying
non-hybrid varieties. Hybrid varieties do require planting dates and seeding rate, crop rotation, planting
favorable growing conditions to reach their full on raised beds, adding to soil organic matter, using
potential. They also must be grown from purchased mulches, irrigating properly and many others. Most
seed, which is expensive because of the labor in- cultural pest control methods are effective against
volved in making the crosses necessary to produce the more than one type of pest. Gardeners should be
seed. Plants grown from seed saved from hybrid familiar with them and use as many as possible.
varieties will vary in numerous characteristics rather
than being identical to the parent plants. Saving seed
of hybrid varieties is not recommended.
Despite these disadvantages, hybrid vegetables
are generally a wise choice for gardeners. They have
increased vigor, pest resistance and longevity, and
seem to be equal in taste and nutrition to non-hybrid
varieties. The fruit, in fact, frequently has improved
shelf life and improvements in both appearance and
quality.
Obtain Quality Seed and Transplants
A last consideration in the choice of vegetables
and varieties is the source of the vegetable seed or Figure 1. Control weeds mechanically while they are
transplants. Seed collected locally may carry a wide small to reduce the need for herbicides.
range of diseases. It may not be true to type and will
not germinate well unless it is stored properly.
Commercially produced seed is much less likely
to carry diseases, because the seed are produced in
areas having low humidity where diseases and insects
6Eliminate Plant Debris Rotate Plant Families
Many insects and diseases survive on plant Rotation of plant families (closely related plants) is
residues. Their numbers decrease markedly as the yet another means of reducing insect and disease prob-
decay process proceeds. Begin by maintaining the lems. Families of plants tend to be susceptible to many of
garden area free from plant debris. Mow or mechani- the same insect, disease and nematode problems. By
cally remove weeds before they produce seed. Indi- grouping vegetable plants into families and moving each
vidual plants of some weeds can produce as many as family to a different location within the garden every year,
a million seed. Remove dead, dying and spent veg- many insect and disease problems can be reduced. Table 1
etable plants from the garden or chop them into pieces lists several vegetable groups which can be rotated to help
and turn them under as soon as harvest is complete. reduce pest problems.
This will speed up decay and reduce potential for
disease and insect buildup by removing overwintering Table 1: Examples of Crop Groupings
sites of insects and diseases. to Reduce Diseases1
Multiple plowings or tillings will not only insure
that all plant residues are worked into the soil where Group Crop Disease(s) Reduced
they will rapidly decay, but will mechanically elimi-
nate many soil insects such as grubworms, cutworms Group A Cantaloupe Microdochium
and wireworms. Working the soil several times is Blight
especially important in gardens that have previously Cucumber Fusarium Wilt
been in sod for several years, as soil insects are likely
Pumpkin Gummy stem blight
to be present in the sod in large numbers. Weed seeds
Squash Anthracnose
will germinate as they are brought to the surface and Watermelon Scab
be killed as the soil is worked. This can reduce future Belly rot
weed problems. Angular leaf spot
Soil free from surface plant debris and organic Nematodes
mulches will also dry out earlier in the spring so it can Group B Brussels
be worked and planted. This is important because sprouts Black leg
cool-season crops must be planted early if they are to Cabbage Club root
mature before summer heat halts their growth and Cauliflower Black rot
reduces yield and quality. Collards
Lettuce
Mustard
Increase Soil Organic Matter Radish
Turning plant debris under also increases soil Rutabaga
organic matter. This is discussed in considerable Spinach
detail in the “Managing Soils Organically” section of Swiss chard
this publication (p 17). The primary concern here is Turnip
the effect of soil organic matter on nematode popula- Group C Eggplant Bacterial canker
tions. Increasing soil organic matter has been widely Irish potato Early blight
reported to reduce nematode populations. Organic Okra Nematodes
Pepper Potato scab
matter apparently enhances the environment for other
Tomato
organisms that feed on nematodes or directly inhibits Group D Beet Scurf
their growth. Plantings of wheat, oats, cereal rye or Carrot Black rot
French marigolds seem especially effective in reduc- Garlic Wilt
ing nematode populations when grown in mass Shallot Nematodes
plantings and turned under several weeks before the Sweet potato
gardening season. There is no evidence indicating that Group E Sweet corn Smut
scattered marigolds growing in a vegetable garden Group F Bean Fusarium root rot
will significantly reduce insect or nematode popula- Cowpea Nematodes
tions. For more information on nematodes, see Peas Anthracnose
Extension factsheet SP341-L, “Nematode Control in 1
Rotate to a crop in a different group when planting
the Home Garden.” successive crops in the same location in the garden
7Avoid Stress vegetable such as lettuce or radishes planted between
Healthy plants withstand or outgrow problems tomatoes. The cool-season vegetable will mature and
better than stressed plants. Maintain optimum grow- can be harvested before the tomatoes need the space.
ing conditions to reduce plant stress whenever Insects seem to recognize large areas of a single
possible. Develop soils with proper pH, organic vegetable more easily than isolated plants or inter-
matter content, particle size, particle arrangement planted combinations of several vegetables. Insects
(structure) and fertility as recommended in the and disease may also spread more slowly when
“managing soils” section of this publication. Garden infesting interspersed host and non-host plants than
only in locations receiving six hours or more of when in large areas of only one vegetable.
sunlight daily. Sidedress with nitrogen-containing
fertilizers or compost (see Table 5). Choose a well- Time Plantings Carefully
drained site or plant on ridges to improve drainage. Careful timing of plantings is an excellent way to
Plant. recommended varieties at recommended dates, reduce the severity of some problems. Cutworms,
planting depths and spacings. Avoid purchasing plants aphids and root maggots, for example, tend to be
that have been stressed. See Extension PB 901, more severe early in the spring and decline in severity
“Growing Vegetables in Home Gardens,” and SP 291- as temperatures increase and rainfall decreases. Corn,
A, “Growing Vegetable Transplants for Home Gar- however, usually suffers less damage from corn
dens,” for specific recommendations. Supplement earworm, European cornborer and armyworms when
rainfall with irrigation when necessary. Control weeds planted early. The later corn is planted, the more
while they are small, and insects and diseases before severe the damage from these insect pests becomes.
they become severe. The result will be vigorous Virus diseases and pickleworms also tend to increase
plants better able to withstand occasional stress. with later plantings of the vine crops. Know your
potential problems and time plantings to avoid them
Try Companion Planting when possible.
Companion planting is the concept of planting
plants together for their mutual benefit. A tremendous Time Irrigation Properly
amount has been written about companion planting, Many people believe that watering during the hot
but very little has actually been proven about its part of the day causes plants to “burn” or die. There is
benefits. It is obvious that shade-loving plants in the very little, if any, evidence that this is true. Watering
forest benefit from taller plants that shade them. It when it is hot or windy will increase evaporation and
seems reasonable that deep-rooted plants absorb waste water, but is unlikely to directly harm plants.
nutrients from deep soil layers and deposit them on or Watering late in the evening may increase disease if
near the surface as they decay. These nutrients can plants remain wet at night. Any kind of water applica-
then be used eventually by shallow-rooted plants. tion that wets foliage is likely to increase plant foliage
Some plants may benefit other plants by attracting or diseases somewhat. Trickle, drip or furrow irrigation
repelling insects, diseases or nematodes by scent, conserves water and avoids increasing foliage disease
color or various secretions. There is, however, little problems, but can contribute to root rot problems.
consensus as to what combinations are beneficial, and Sprinkler irrigation is probably best done during cool,
specific companion planting recommendations will non-windy morning hours.Another common error in
not be made here. timing irrigation is to apply small amounts of water
It is known that black walnut trees produce a every day or two. This works well when using drip or
substance that inhibits growth and causes wilting of trickle systems where a small amount of water will
many plants. Avoid planting vegetables, especially soak deeply into the soil. When using sprinkler
tomatoes, near black walnut trees. irrigation, however, apply 1 to 1 1/2 inches of water
at one time and then wait several days until the soil
Use Intercropping surface dries before irrigating again. Less frequent
Raising two or more crops in the same area at the irrigation will be less likely to increase plant foliage
same time is called intercropping. Intercropping can and root diseases and will not create a shallow layer
reduce a wide range of pest problems. Common of moist soil over drier, deeper layers. Plants will then
examples of intercropping include either pole beans be less dependent on frequent watering for growth
or pumpkins planted with corn, and a cool-season and even survival.
8Provide Air Circulation Consider Using Solarization
The longer a plant remains wet, the more likely it Solarization offers one of the few non-chemical
is to develop a disease problem. Good air circulation possibilities for reducing some soil insects, nema-
is vital if plants are to dry off promptly and avoid todes, diseases and weed seed simultaneously. This
undue disease problems. Planting on slight slopes or procedure requires bare, moist soil and the hottest
ridges will help. Morning sun is also important in possible temperatures. The best conditions for solar-
drying surfaces as soon as possible. Planting at ization are periods of bright, sunny weather, which
recommended spacings is very important, as are generally occur during the long, warm days of
properly pruning and supporting plants off the summer. Begin the procedure in June or early July.
ground. A pruned and supported tomato, for example, To solarize soil, first remove all vegetation. Work
receives better sunlight because of reduced foliage the soil as if it were to be planted, and water with as
and better air circulation. Fewer aphids colonize the much water as it will comfortably hold. Cover the
drier plant and it is easier to spray if sprays are used. saturated soil with a sheet of clear plastic stretched
The fruit are also held off the damp soil and are less tightly over the soil. Place 1 inch cubes of wood or
likely to rot. If vegetable plants are spaced and plastic foam on the plastic about a foot apart. Cover
supported properly, many problems will be reduced. the grid with another clear sheet of plastic so you
have two sheets of plastic with a 1-inch air space
Use Mulches between them. Seal the edges with soil. Leave the
Mulches may reduce certain pest problems, but plastic in place one to two months. During sunny, hot
can increase others. Mulches reduce plant stress, days, the soil temperature should reach 120 degrees F,
prevent weed growth and maintain soil moisture. or more, at a 2-inch depth, which will reduce the
They may reduce some insect and disease problems, population of many soil pests. If only a single sheet of
as well as increase soil tilth and organic matter. plastic is used, temperatures will not be as high or stay
Mulches are discussed more extensively in this high as long, and the treatment will be less effective.
publication under “Barriers” (p.11). The soils section After solarization, it is very important that soil not be
of this unit also contains a discussion of mulches as worked deeply. The deeper soil is worked, the more
they affect soils. Extension factsheet SP291-H, likely it is that disease organisms and weed seed will be
“Mulching Vegetable Gardens,” discusses the benefits brought to the surface where they will grow.
of mulches and how to mulch gardens with both
organic and inorganic mulch.
ample soil to anchor plastic squares of styrofoam insulation, bricks, two layers of plastic
during strong storms or wood separating plastic sheets sheeting
Figure 2. Soil solarization procedure.
9Avoid Introducing Pest Problems A second method of supporting tomatoes is with
Plant diseases, nematodes, weed seed and even wire cages constructed from concrete reinforcing
insects can be carried from place to place on equip- wire. Cages should be 20 to 22 inches in diameter,
ment, introduced into the garden with transplants or which requires a 6-foot length of wire bent into a
moved by insects and human hands. Keep equipment circle. Firmly anchor each cage so it will not blow
clean. Remove soil from tillers and garden equipment over. Cages may be anchored by tying them to stakes
after using them. This is especially important if they or by tying them to a wire that is attached to posts at
are to be moved between farms, fields or even parts of each end of a row of cages.
the yard. Set a single tomato plant in each cage. Allow the
Transplants grown in pasteurized soil or artificial plants to grow without pruning. Push the ends back
media will be less likely to harbor pests. Purchase into the cages as they grow out. Harvest fruit by
transplants certified free of insects and disease if reaching through the mesh.
possible. Always inspect transplants for the presence Grow caged cucumbers like caged tomatoes but
of insects and diseases before purchasing them. use a 10-foot length of concrete reinforcing wire. This
Avoid the use of tobacco if you grow tomatoes, will make a 3-foot diameter cage that will probably
peppers or Irish potatoes. Tobacco contains tobacco not need anchoring. Plant cucumbers 6 to 10 inches
mosaic virus (TMV) which will get on your hands apart around the outside of the cage. Push the grow-
and be spread to plants which you touch. Equipment, ing vine tips into the cage until they begin to climb. A
insects or anything touching an infested plant and small hollow in the center of the cage makes a
then another plant is also likely to transfer the disease convenient place to fertilize and water the cucumbers.
from plant to plant. TMV is very hard to control and Benefits of this system include more fruit, an ex-
reduces both fruit set and fruit size. Total yield of tended harvest season, increased ease of harvesting
TMV-infested plants may be reduced slightly or and reduced disease pressure.
nearly wiped out. Leaves of infested plants may be
distorted and will probably have a mottled appearance OtherAlternatives
rather than a solid green color. Remove isolated plants
Several things can be done to prevent some
showing these symptoms as soon as they appear.
insects and diseases from reaching plants. Methods of
controlling certain insects without using insecticides
Use Plant Supports
are also available. Most of these are compatible with
Plant supports can be an important part of the
the organic gardening philosophy and can be of help
organic garden. They make plants easier to tend and
to gardeners.
harvest and extend the harvest season. More impor-
tantly, supported vegetable plants have fewer disease
and insect problems because of improved air circula- Barriers
tion and less contact with wet, disease-infested soil. Several types of barriers can be used to prevent
Tomatoes, English peas, sugar snap peas, cucum- certain insects from reaching a plant or plants. Small
bers and pole beans are some of the vegetables that paper or plastic cups with the bottoms removed, for
are commonly grown on supports. These vegetables example, can be pushed into the ground around young
may be trained on a fence, in a wire cage or on a transplants to protect them from cutworms. Alumi-
trellis. Pole beans may be grouped around individual num foil wrapped around young plants will serve
stakes or several stakes may be pulled together at the much the same purpose. Six-inch lengths of sewer
top and tied for additional strength. Trellises may be pipe may also be placed over young plants as a
constructed from cane supported by a wire on top, combination cutworm barrier and windbreak. Nylon
string woven between top and bottom wires or from bird mesh or mesh berry baskets placed over the
nylon netting. plastic cups or sewer pipe will protect young seed-
Tomatoes respond especially well to vertical lings from birds.
culture, since many of the fruit may rot if they touch
the ground. Tomatoes are usually supported by 5-or 6-
foot stakes or a trellis. Use stakes at least 1 1/2 inches
square and drive them a foot or more into the ground.
Plants are pruned to one or two stems and tied loosely
to the support at 8- to-12-inch intervals.
10cucumber beetles off. Spun-bonded row covers
should be applied loosely so they can be lifted by the
plants as they grow. Heavy rain may cause the covers
to become stuck to mineral soils, requiring re-loosen-
ing of the covers. Apply them immediately after
planting before insects attack the plants. Remove
covers from cucumbers and other plants requiring
pollination when the plants begin to flower. Water
will pass through spun-bonded row covers, but a
small amount of heat will be retained as an additional
benefit of this material. Controlling weeds growing
Figure 3. Mechanical barriers can reduce cutworm beneath the covers may be a severe problem. Remove
damage to young plants. the row covers when it is cloudy and water the plants
to reduce shock.
Mulches, both plastic and organic, can serve as a
barrier against diseases that are spread partially by
soil splashing onto plants. Early blight and buckeye
rot of tomatoes are examples. Mulches will not
eliminate these diseases, but may delay their onset
and eventual severity. Organic mulch applied around
tomatoes while the soil is still cool may delay ripen-
ing a few days, but black plastic mulch will warm the
soil and speed ripening.
Figure 4. Netting will prevent birds from feeding on
bush fruits and small fruit-bearing trees.
Diatomaceous earth, a chalk-like substance
consisting of microscopic, sharp, shell particles,
sprinkled around young plants may protect them from
slugs, snails and some soft-bodied insects. Wood
ashes are reported to have the same effect. Figure 5. Apply organic mulches 2 to 3 inches deep
Individual collars placed around cabbage or around established plants after the soil warms up.
broccoli will frequently protect them from root
maggots. Cut 6-inch squares or disks of foam rubber,
carpet padding or tarpaper. Punch a small hole in the
middle and make a slit from the edge to the hole. Fit Mulches also reduce numbers of some insects,
the barriers tightly around vulnerable plants and cover such as Colorado potato beetles, by preventing their
each barrier with enough earth to hold it down. emergence from the soil where they overwintered and
Hot caps, small domes made of translucent paper, by slowing their migration from weedy overwintering
may also prevent insects or disease spores from sites to plants in the garden.
reaching individual plants. Other barriers can protect Gardeners should be aware that mulches can
entire rows of plants. Spun-bonded row covers, for serve as hiding places for some insects and increase
example, can be placed over young plants of the the incidence of some diseases by retaining too much
cabbage family to exclude various cabbage feeding water around plant roots. Black plastic, for example,
insects, or over cantaloupe and cucumbers to keep may increase damping off and root rot of peas and
11beans, or bacterial diseases of tomatoes. This is the garden. Pheromone traps may provide adequate
especially true when it is used around seedlings control of several pest species.
growing in poorly-drained soil. Light traps have been used outdoors for control of
various flying insects. There is little or no evidence
Repellents that light traps adequately control many garden
It would be great to be able to use a repellent to insects.
keep insects from bothering plants but, unfortunately, Sticky red spheres or sticky yellow traps will
there are no effective, broad-based repellents. Some attract and trap a variety of insects. They are better
gardeners have used solutions made from hot peppers, used to monitor insect populations than to control
garlic or strong-smelling herbs to discourage insects. specific insect species.
It is unclear whether these solutions are toxic to some
insects, repel them or work at all. The Extension Baits
Service has no data regarding their usefulness but Sometimes pests can be attracted away from
cautions that these solutions are seldom legal to use growing vegetables and killed. Some slug baits, for
on vegetables grown to be sold. example, can be placed in small piles on boards or in
Reflective plastic mulch in various colors and containers. Slugs are attracted to these baits, eat them
aluminum foil mulch can be used to repel thrips and and die.
aphids on some vegetables. Reducing aphid and thrips Another way to trap slugs is to place shallow
infestations may also reduce the spread of viruses containers filled with beer in the soil with the top of
carried by these insects. These mulches apparently the container level with the soil surface. Slugs will be
confuse thrips and aphids, making it more difficult for attracted to the beer and drown. A solution of 1 pound
them to locate vegetable plants. of sugar and 1 teaspoon of yeast in a gallon of water
Mulch the area under very young plants com- fermented two or more days works well. This makes
pletely for best results. However, mulching too early use of both the trap and the bait concept.
may prevent the soil from warming up and delay All of these baits must be replenished frequently.
maturity. It may also be necessary to provide holes in Traps need to be cleaned and refilled. Baits will last
the mulch to allow moisture to reach the plant roots. longer if some sort of a cover is provided to keep rain
Numerous repellents have been used to keep from diluting or destroying them.
moles from gardens. These include caster beans,
gopher spurge, windmills, etc. Their common trait is Birds
that none of them produce consistent results. The best Many birds eat large amounts of insects or weed
way to eliminate moles is to trap them. Mole traps are seed. Encouraging these birds can greatly reduce
difficult to use properly, but can be very effective. insect and disease problems in home gardens. Encour-
More detailed information can be found in Extension age birds by planting berry-forming shrubs and small
factsheet SP293-A, “Mole Control in Tennessee.” trees, by providing a source of water (a bird bath) and
by providing nesting sites and birdfeeders. Extension
Traps factsheet SP239-D, “Building Bird Houses,” dis-
Shingles, boards and even inverted cabbage cusses construction of a wide range of bird houses
leaves placed in the garden will collect slugs, cut- and how to locate them.
worms, squash bugs and other pests that hide in Some birds also consume vegetables. Do not
moist, dark places. They can be collected from these permit any seed to remain visible on the surface of the
hiding places and destroyed by dropping them into a ground when planting vegetables. It may also be
container of water covered with a thin layer of oil. necessary occasionally to make use of netting or
Pheromone traps are mechanical devices contain- spun-bonded row covers to protect vegetables from
ing scents that attract a specific insect species. birds. Imitation snakes, owls and hawks repel birds
Pheromone traps are available for Japanese beetles only if they are moved frequently from place to place
and a wide range of other insects. The insects are and then only for a short time. Plastic foam cups
enticed into the trap by the scent and are unable to get inverted over corn ears after pollination may protect
out. These traps attract pests from a considerable ripe corn ears from blackbirds.
distance, but do not immediately catch all the insects
they attract. They are best used some distance from
the garden to attract the insects away from, not into,
12Beneficial Insects study the insect’s life cycle to determine how best to
Most insects are neither particularly harmful nor assist or control it. Table 2 lists some common
beneficial to home gardens. It is important to identify beneficial insects and the pests they feed on.
the insects present in a garden to determine whether
or not controls are needed. It is also important to
Table 2. Some Common Beneficial Insects
Insects Description Pest(s) Controlled
Ground Beetles Large, shiny, dark brown Feed on caterpillars, armyworms and cutworms
beetles
Ladybugs Small, round, colorful beetles; Feed on aphids, mites, scale and many insect eggs
blue-yellow striped larva
Predaceous Stink bugs Medical shield shape Feed on many insects
Ambush Bugs Large, dark bug with long, Feed on whatever they can catch
narrow head
Tachnid flies Drab small fly Parasitize many insect larvae
Lacewings Stalked egg 1 inch long insect Feed on aphids, mites, scale insects and many insect
lacy wings eggs
Praying Mantids 3-inch long insect with Many insects
triangular head
Predatory Mites Very small, 8 legs, Spider mites
not true insects
Some gardeners purchase and release various beneficial insects, you should learn not only which
beneficial insects into their garden to control harmful insects are beneficial, but also which host plants
insects. A variety of companies sell beneficial insects. encourage which insects. Unnecessary chemical
Extension factsheet SP290-Z, “Commercial Sources for applications should also be avoided if beneficial
Predators and Parasites,” lists several such companies. insects are to be encouraged.
Lady bugs and many other beneficial insects are
extremely mobile and may not stay where you put Handpicking
them. Others such as preying mantids will consume Gardeners may control some insects by handpick-
each other. Introducing large numbers of insects into a ing. This method of control is most successful in
small garden may be of limited value. Encouraging small gardens and with large insects that are present
natural populations, however, can be very helpful. in small numbers. Tomato hornworms, squash bugs,
Begin by growing a variety of vegetables in the cabbage worms, Colorado potato beetles and other
garden. Allowing natural vegetation to survive near large insects may be controlled this way. After insects
the garden may increase beneficial insects, but may are removed from the plants, they may be killed by
also increase harmful insects. To successfully use crushing or being dropped into a container of soapy
13water or water covered with a thin layer of oil or soap solution will be effective. Use the more toxic
kerosene. While handpicking squash bugs, also crush chemicals only when less toxic sprays will not do the job.
or remove the reddish or bronze egg masses found on Lastly, always follow the label. Any material sold
or under the leaves. as a crop protection chemical in the United States
Insects such as blister beetles and some caterpil- must be registered with the Environment Protection
lars can sting or burn when they are touched. Wear Agency (EPA) and labeled. The label must be fol-
gloves or learn to identify common garden insects. lowed. Failure to do so is illegal and can be danger-
ous. Labels list time and rate of application and the
vegetables and pests on which the product can be
ProtectiveChemicals used. They also contain other information, such as
Sometimes the severity of a pest problem in- safety precautions. Always read the label and use the
creases until the gardener must either actively control chemical only where and how it is permitted. It is
the problem or lose yield and quality. Following the possible to cause severe environmental or bodily
basic principles of pest control will make control injury if agricultural chemicals are misused. In no
easier, more effective and less damaging to non-target case does the Agricultural Extension Service recom-
organisms. mend the use of any plant protection substance in a
Begin by inspecting the garden frequently. Walk manner inconsistent with its label.
though it several times a week looking for weeds,
insects, diseases, plants that need pruning or staking,
rows that need thinning, etc. The first step in control- NaturalProtectiveSubstances
ling a pest problem is to recognize its presence. Water
Next identify the problem. Many agricultural The simplest natural substance for removing
chemicals work on only one, two or a few pests. insects from plants is water. A forceful stream of
When the problem is identified, select a pesticide that water may be applied to the underside of plant leaves
will control the problem but damage few other with any type of sprayer or even with a hose and
organisms. A properly selected treatment is more nozzle. Aphids, spider mites, thrips, whiteflies and
likely to be effective and less likely to damage other small pests can be dislodged and washed to the
beneficial insects and other non-target organisms. ground. Many will be unable to find their way back
Line drawings of common garden insects and onto the plants and may die. Repeated treatments may
their description are shown in Extension PB 595, be required to destroy all pests. More pests may hatch
“You Can Control Garden Insects.” This publication from eggs or mature from crawling stages that cannot
and other Tennessee publications mentioned are be washed from plants. Be aware, however, that the
available to Tennessee residents at no charge at UT more frequently water sprays are used, the more
county Agricultural Extension Service offices. County disruption of natural enemies may occur. Frequently,
Extension personnel can also assist in identification of water sprays may also increase plant disease prob-
insects, diseases and weeds. lems, especially if plants remain wet at night.
Begin control practices early. Plant diseases can
sometimes be halted, but they can seldom be re- Bug Juice
versed. If damage is too severe when control mea- Many organic gardeners have had success in
sures are begun, losses in production and quality will controlling some insects using diluted solutions
occur. Control insects while they are immature and containing ground up caterpillars or mature insects.
few in numbers. The more mature the insects and the Anywhere from a few individuals to a half a cup of
larger their populations, the more difficult they are to insects are collected and blended with two cups of
control. water. The liquid is strained through cheesecloth,
Sprays are generally more effective in controlling diluted and used to spray vegetable crops. Success is
insects and disease than dusts. not consistent. Success is more likely if dead or dying
Sprays cover the complete surface of the plant. insects are used, since they are more likely to be
Sprays are also easier to apply to the bottom surface diseased and spread the disease to other insects. This
of leaves than dusts. Many insect problems begin on technique may be more successful when used in
the bottom surface of the leaf rather than the top. Use combination with other biological sprays. Do not use
the least toxic spray that will be effective. Sometimes your household blender.
a stream of water, horticultural oil or an insecticidal
14Hot Pepper Microbial Agents
Hot pepper sprays are also widely used by “Bacillus thuringiensis” (Bt) is a type of bacte-
organic gardeners. One half cup, or more, of hot rium that kills certain harmful insects and is harmless
peppers are chopped or ground, then mixed with a to beneficial insects. The most common forms of Bt
pint of water. The mixture is allowed to stand a day or are sold under the tradenames DipelTM, ThuricideTM
two, then strained and sprayed on the infested plant. and MVPTM. They are effective against the larva of
Be careful not to get this spray in your eyes and be butterflies and moths and may be used on a wide
sure to wash your hands. Sometimes crushed garlic, range of plants. They can be reapplied as plants grow
onions or strong-smelling herbs are added to these within the limits listed on the labels.
sprays. There are many, many recipes that have been A new form of Bt, sold as M-oneTM, is effective
tried. A garlic repellent is also commercially avail- against Colorado potato beetles. Other forms of the
able. Unfortunately, home remedies are neither bacterium are being investigated and may soon be
labeled for use as pesticides, nor does The University available to control additional insects.
of Tennessee have information concerning their Another bacterium, “Bacillus papillae”, causes
effectiveness. Their use is not recommended. milky spore disease in grubs of Japanese beetles. This
product is commercially available as DoomTM or
Soaps JapademicTM but may be very hard to locate. The
Many types of soaps have been used to kill, powder is applied to the ground and, in time, infects
dislodge or repel certain garden pests. They vary the grubs over large areas. Once established, the
greatly in effectiveness and in toxicity to plants. They bacteria may survive in the soil for several years.
are frequently effective against thrips and other small,
soft-bodied insects such as aphids, mealybugs and Sulfur
whiteflies. Their disadvantages are that they are Sulfur may be used to control certain fungal
expensive and they need to be reapplied frequently, diseases of a variety of vegetables, fruits and grains as
possibly every three or four days. well as several kinds of mites. It is one of the few
Several commercial brands of soap are especially substances used by organic gardeners to control
formulated and labeled for use on garden vegetables. diseases. Some organic gardeners do not use sulfur
Some of these may be mixed with other pesticides to because of the possibility that it might disrupt soil
increase the effectiveness of both. Commercially microorganisms. It can also have a negative effect on
labeled soaps are the only soaps recommended for use beneficial insects and burn plants when used during
in the home garden. Be sure to use them only as hot, humid weather. Products that contain sulfur
recommended on the label. include Wettable Sulfur (recommended for commer-
cial use only), ThioluxTM, Lime-Sulfur and several
Oils combinations of sulphur and other materials generally
More than one grade of oil can be used as a spray acceptable to organic gardeners.
on horticultural plants. Most are heavy-grade oils
suitable for use only on dormant plants. The newer, Copper
lighter-weight horticultural spray oils are thinner and Basic copper sulfate, copper oxychloride sulfate
can be tolerated by many growing plants. They work and derivations of these products are used to control
by suffocating mites, scales and soft-bodied insects, mildews, rots, blight and leafspots on many crops.
and may be the preferred method of controlling some These can be effective but may also damage plants.
scale insects. Use them precisely according to the Be sure to follow the label precisely and to observe
label to avoid crop damage. all precautionary statements.
Mineral oils are also used to reduce corn earworm
infestation. Two or three drops applied to corn silk Other Protective Chemicals Used by
with an eyedropper may protect the ear from infesta- Organic Gardeners
tion by corn earworms for a few days. Do not apply Sodium hypochlorite, also called common
until the silk has wilted and begun to turn brown on household bleach, has been used as a seed treatment.
the ends or pollination may be affected. Seeds are soaked for one minute in a solution contain-
ing one part bleach and 10 parts water. This solution
may also be used to sterilize pruning shears, grafting
15tools and seeding containers to reduce the spread of Soils are important to plants because they provide
disease-causing agents. support and supply plants with water and nutrients.
Avermectin (AvidTM) is a product used in com- Growing plants remove large amounts of water and
mercial crop production. The chemical is produced by smaller amounts of nutrients and gases from soils.
bacteria and is used to control leafminers and spider The nutrients removed are especially significant when
mites. Sodium aluminofluoride or cryolite plants or plant parts are harvested, as is the case with
(KryocideTM) has been used for many years in organic gardening. Therefore, gardeners must return nutrients
crop production. This product is used to control several to the soil and maintain the soil’s ability to retain
types of insects on a wide variety of crops. them until they are required by growing plants. There
ClandoSanTM is a chitin protein found in crusta- are two approaches to this problem, that of traditional
cean shells and is labeled for nematode control. agriculture and that of organic farming and gardening.
ClandoSanTM is a new product still being evaluated. Traditional agriculture views soil as a relatively
The product acts to stimulate the growth of certain inert holder of moisture and nutrients. Effort is made
soil microorganisms that produce chitanase and other to conserve the soil, maintain its structure and resup-
enzymes that destroy plant-pathogenic nematodes. ply nutrients and water as they are removed. The
easiest and cheapest way to supply water is through
Botanically-Derived Chemicals irrigation. The easiest way to supply nutrients is in the
Several insecticides are extracted from plants. most concentrated form, high-analysis chemical
These are frequently referred to “botanical insecti- fertilizers.
cides.” Five of the most common include pyrethrin, Organic gardeners consider soil to be a complex
rotenone, ryania, sabadilla and neem. These are system which includes lifeforms, gases, water,
sometimes used by organic gardeners because they minerals and organic materials. Chemical fertilizers
are effective against many insect pests and because are viewed by most organic gardeners as too harsh to
they quickly break down into substances thought to be applied to living soils. They are believed to
be harmless. Gardeners should follow the same contribute to the loss of proper soil function and to
precautions when using these insecticides as when restrict the life processes of beneficial organisms that
using any other insecticide. Always follow the label. recycle nutrients and contribute to the health of living
Use the insecticide only on the vegetables, at the soils. This section will attempt to assist the organic
times and in the concentrations for which it is labeled. gardener in maintaining or improving the ability of
Even botanicals are toxic and care must be followed garden soils to support and provide nutrients to
in applying them. Special restrictions should be noted vegetable plants.
if environmental damage is to be avoided. Rotenone,
for example, is 10 times more toxic to people than Maintaining or Increasing Soil
Malathion and is very dangerous to fish. Sabadilla is Organic Matter
toxic to bees. Lastly, remember that botanical insecti- High soil organic matter is the basis of managing
cides will not differentiate between beneficial and soils organically. Organic matter improves soil
harmful insects and may severely damage populations structure so it will hold water and oxygen and be
of beneficial insects. easier to work. It greatly increases the microbial
content of soils, which is sometimes thought to reduce
ManagingSoilOrganically a plant’s chances of becoming diseased. Most impor-
tantly, soil organic matter plays a large role in storing
Introduction and releasing nutrients for plant use.
Soils consist of a combination of gases, water, Soil organic matter is a product of the decay of
minerals and organic compounds. They vary greatly plants and animals. It usually includes a large number
in how much of each of these they contain, the size of of things in various stages of decomposition. Most
the particles, particle arrangement and in the compo- plant and animal materials break down rapidly at first,
sition of each of the four individual components. then more slowly as the easily decomposed parts
There are also differences in the amount and types of disappear. All of these plant and animal residues are
living organisms found in soils, in the ability of soils collectively referred to as organic matter. The fraction
to hold or release water and in nutrients. of organic matter in a relatively advanced state of
decay, now decaying only slowly, may be referred to
as humus.
16The amount of organic matter in a soil is a year and light feeders the third year. This is an
balance between the amount produced and the amount example of a three-year rotation.
lost, mostly through decomposition. More is produced
with long growing seasons and soils that support Green-Manure Cover Crops
vigorous plant growth. More is lost in warm-moist Green-manure cover crops are usually planted in
climates, and in soils rich in oxygen and soil microor- late summer or early fall and plowed under either late
ganisms. Coarse soils usually contain less organic in the fall or several weeks before spring planting.
matter than fine soils. The more soil mixing that They provide large amounts of organic matter, some
occurs, the greater the potential for decomposition. nutrients and protection from erosion over the winter.
Because Tennessee has a warm, moist climate, They are useful to gardeners trying to improve their
relatively large amounts of organic matter are decom- soils, especially those who are unable to compost
posed annually. Because of this, organic matter will enough material for their large gardens. They may also
quickly decrease to less than 1 percent in Tennessee be used over the growing season in a rotation system
soils unless it is replaced. designed to control plant pests or improve soils.
Organic gardeners utilize a wide range of proce- There are two types of green-manure cover crops,
dures to increase soil organic matter. Some of these legumes and non-legumes. Legumes can add nutrients
follow. to the soil because they have root nodules that contain
. nitrogen-fixing bacteria. They fix more nitrogen when
Using Crop Residues mixed with a non-legume crop in the garden than
Crop residue is the portion of plants remaining when grown by themselves. It is not unusual for a
after harvest. This residue is a significant source of mixed legume planting to fix 100 pounds of nitrogen
organic material. It can be left on the surface where it per acre. Legumes may also have very deep roots,
grew, used as a mulch, composted or turned under. which improve soil drainage and bring up nutrients
Leaving crop residue on the soil surface where it grew from the subsoil to levels where shallow-rooted plants
or around plants as a mulch allows it to help control can use them. Peas, beans, clover, vetch and alfalfa
soil erosion. Breakdown of the organic material is are examples of legumes.
slowed so total soil organic material increases. It may, The non-legumes used as green-manure cover
however, increase insect, disease and weed problems crops are mostly grasses. They are grown because
due to these pests overwintering in this debris. they are economical, easily established and can
Turning crop residue under breaks it down faster, quickly produce large amounts of organic material.
which may release nutrients. Some insects and Examples include annual rye, oats, wheat and millet.
diseases are also less likely to survive if their host A list of suitable green-manure cover crops and
plant material is eliminated. some of their characteristics is contained in Table 3.
Crop Rotation
Crop rotation is a regular scheme of planting
requiring that a different crop be grown in a given
location each year for two, three, four or more years.
The section concerned with pest control (p 8) dis-
cusses rotation for that purpose and makes specific
recommendations concerning groups of plants to
rotate. Crop rotation can also play a part in maintain-
ing soil high in organic matter and fertility. Some
vegetables, such as Irish potatoes, tomatoes, canta-
loupe, corn and the cabbage family, are heavy feeders
and remove large amounts of nitrogen, phosphorus
and potassium from the soil. Others, such as root
crops and herbs, are light feeders. Legumes have the
ability to absorb and hold nitrogen from the air and
can actually add nitrogen to the soil. One might plant
heavy-feeding vegetables in a given area the first
year, a legume green-manure cover crop the second
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