Organic Vegetable Gardening

University of Rhode Island GreenShare Factsheets

Organic Vegetable Gardening

Organic gardening differs from "conventional" gardening mainly in the areas of fertilization and pest control. The organic gardener prefers to use natural and organic materials and methods, avoiding practices and synthetic chemicals that may be detrimental to his health or environment.

The information in this publication should be beneficial to all gardeners regardless of methods of culture used; however, it is primarily intended to aid the organic gardener to employ workable methods acceptable to him and compatible with the philosophy of "organic gardening."

SOME EARLY PLANS

Choosing a Location -- Select a plot of good, well-drained soil near a water supply. It should be close to the home for convenience, but should not be shaded by tall buildings or trees. Enclosing the garden spot with a fence is usually profitable.

The Garden Design -- Many gardeners find it helpful to draw out on paper the location of each row and the crop or succession of crops to be planted.

PLANTING GUIDE

See our GreenShare Factsheet series on vegetable culture for information specific to different vegetables regarding planting dates, harvest, yield, etc.

SOIL PREPARATION

Since organic fertilizer and soil conditioning materials are slow working in general, they should be mixed into the soil at least three weeks ahead of planting and the soil thoroughly prepared for the seed or transplants. Clumps of unrotted organic materials not only interfere with the seeding operation, but may result in nutrient deficiency and soil-borne diseases problems such as "damping-off" of young seedlings.

ORGANIC MATTER

A major basis for organic gardening is the use of abundant quantities of organic material applied to the soil. Usually, it is in the form of animal manures, plant manures, cover crops, compost or mixed organic fertilizer.

Benefits of Adding Organic Matter

Improves tilth, condition and structure of soil
Improves ability of soil to hold water
Improves ability of soil to hold nutrients
Improves "buffering" capacity of soil--keeps soil from "over-reacting"
Supports the soil's microbiological activity
Contributes nutrients, both minor and major
Releases nutrients slowly
Acids arising from the decomposition of the organic matter help to convert insoluble natural additives such as ground rock into plant-usable forms
Helps vegetables survive stress, as from nematodes
Helps dispose of organic waste products

What Happens to Organic Matter Applied to the Soil or Compost Pile?

Under suitable conditions, the organic matter is decomposed by micro-organisms such as fungi, algae, bacteria, molds and earthworms. In the process, insoluble and unavailable (to plants) nutrients, such as nitrogen, are gradually changed into simple usable products.

For example, nitrogen is converted from the unusable organic forms to a usable inorganic form through the process called nitrification, which is the breakdown of protein (organic nitrogen) into ammonia and then nitrate. Some of the organic matter becomes part of the soil humus.

Proper Conditions For Nitrification

First, materials containing nitrogen must be present. There is a great variation in the amount of nitrogen the different organic materials contain. Certain soil or compost conditions are also necessary:

Proper soil acidity (pH) --should be about 7.0; in acid situation below 5.5 nitrification ceases
Proper temperature of soil -- above 50ÐF
Good aeration -- (does not occur with wet, soggy soil or compost)
Adequate lime for use by micro-organisms (and to avoid acidity)

ANIMAL MANURES

Where animal manures are available, they are probably the best source of fertilizer and organic matter for the organic gardener. Use manure which has been aged for at least 30 days, or composted.

Manures vary greatly in their content of fertilizing nutrients. The composition varies according to type, age, and condition of animal, the kind of feed used, the age and degree of rotting of the manure, the moisture content of the manure and the kind and amount of litter or bedding mixed in the manure. Animal manures provide most of the micro-nutrients needed. Some manure products are composted, rehydrated or mixed with plant litter to enhance their fertility.

How Much to Apply Broadcast Before Planting

Cow, horse, hog -- A minimum of 25 pounds per 100 square feet (about 5 tons per acre) of garden soil. For best results, supplement each 25 pounds of manure with 2 to 3 pounds of ground rock phosphate or raw bone meal. Use up to 1 pound per square foot.
Poultry, sheep -- Apply at least 12 pounds per 100 square feet (about 3 tons per acre minimum) - or as much as 3 - 4 inches (20 tons per acre)
Other animals--rabbit, goat, and exotic grasseaters -- 10-12 pounds/100 sq ft. minimum, up to 100 lbs. per sq. ft.

After Planting (As a sidedressing) if needed

Cow, horse, hog -- Sidedress with up to 5 pounds per 100 square feet of row.
Poultry, sheep -- Use up to 3 pounds per 100 square feet of row.

How to Apply

All Types -Broadcast evenly over plot and spade, roto-till or otherwise work into topsoil. Apply three or more weeks before planting. A small amount may be mixed well in the planting hole; however, plant injury may occur with 1 lb. or more placed in the hole.

How to Apply as a Sidedressing

All Types -- Scatter a band of manure down each side of the row. Place each band at the edge of the root zone and work lightly into the soil surface. For individual plants, open a furrow encircling the plant and fill with manure, then cover.
If a mulch is present, rake it back at the edge of the root zone in order to apply the band of manure, then re-cover with the mulch.

NOTE: Manure is not always a complete, well-balanced fertilizer. It is advantageous to broadcast a complete organic fertilizer (such as Fertrell) or ground rock phosphate and potash in addition to the manures.

COMPOSTS

Acceptable manure-like organic fertilizer (artificial manure) may be obtained through the process of composting. Simply put, compost is made by alternating layers of organic materials, such as leaves and kitchen table refuse, with manure, topsoil, lime, organic fertilizer, water, and air, in such a manner that it decomposes, combines, and yields artificial manure. See our GreenShare Factsheet on composting for specific compositing recommendations.

Use of Compost in the Garden
Since compost is artificial manure, it should be used much as you would manure. Broadcast it over the entire garden three weeks or more before planting. Or if you have only a small quantity of compost, it may be mixed into the soil along each planting furrow or at each hill site. As a minimum, apply it at the rate of about 25 pounds per 100 square feet, or 1…4 pound per square foot. Larger amounts are even more beneficial, up to 200 lb/100 sq ft. (2 lb/sq ft.). Caution: If your compost is made from mostly woody materials, it may temporarily deplete the nitrogen from the soil and plants; be sure to mix manure with it when applying.

NATURAL AND ORGANIC FERTILIZERS

Natural and organic materials which yield plant nutrients upon decomposition are often available for purchase either separately or in combination. These materials may be applied to the garden separately or combined, used in the compost pile, or mixed with manure.

Natural Deposits (Rocks, Sands, Shells, etc.)
Such naturally occurring materials are usually not easily obtained in today's modern agriculture; however, where available they represent sources of mainly potash, phosphorus, and lime (calcium and magnesium) for organic gardeners.

Phosphorus -- Rock phosphates are natural deposits of phosphate in combination with calcium. The material as dug from the earth is very hard and yields its phosphorus very slowly. When finely ground and with impurities removed, the powdery material is only slightly soluble in water, but may be beneficial to plants in subsequent seasons following application. The reaction of phosphate rock with acids from decaying organic matter in the garden or compost tend to make the phosphorus available to garden plants. Collodial phosphate is also available and widely used. Apply both phosphates at the rate of 2-5 pounds per 100 square feet of garden soil. Or, when applying manure or compost, mix at the rate of 21…2 pounds phosphate per 25 pounds manure or compost. Broadcast the material over the soil surface and work into the topsoil at least three weeks before planting. Manure or other organic fertilizer should be added at this time. Since the materials are so slowly decomposed, sidedressings are seldom beneficial.
Potash -- Potassium is widely distributed in nature, occurring in rocks, soils, tissues of plants and animals and water of seas and lakes. In gardening practice, materials such as wood ashes, tobacco stems, wool suint, seaweed, potash salts, greensand and ground rock potash are used alone, in combinations with other materials yielding other nutrients, mixed with manure or in compost piles. Since the potash bearing materials vary so much in composition and rate of decomposition, specific application rates must be determined for each material and its combinations. In general, ground rock potash at 5 pounds per 100 square feet may be broadcast over the soil surface three weeks prior to planting and spaded in. Langbeinite (Sul-Po-Mag) is used at 1 lb/100 sq ft.
Micro-nutrients -- An advantage for using organic materials as fertilizers is that they contain many of the elements also needed by the plants in addition to N, P and K (for example, manganese in manure). Besides the general amounts of micronutrients found in most organic materials, certain ones are concentrated into such naturally occurring materials as gypsum (calcium and sulfur), marl (calcium), dolomite (Calcium and magnesium), limestone (calcium), basic slag (iron, calcium, manganese and magnesium) and finely ground borosilicates.
Lime -- Reducing the acidity of the soil is the primary purpose for using lime in the garden. However, liming materials also provide nutrients for plant use. Calcium and magnesium are the two elements most commonly provided by lime. Gypsum is used where more calcium is needed without raising the pH. Natural deposits of lime which are an organic gardener might use are limestone, dolomite, shell and marl. All these forms must be finely ground to provide maximum benefit to the soil and plants. Dolomite is preferred due to its content of both calcium and magnesium. Lime to sweeten the soil should be applied only when the needs have been established by a reliable soil test. See our GreenShare Factsheet on soil testing for more information. Apply lime well in advance of the planting date, preferably 2 to 3 months before the garden is planted. Mix well with the soil and keep moist for best reaction. Application closer to planting time is permissible, but its benefits are delayed.

IRRIGATION

Thoroughly wet the soil once a week unless sufficient rain falls to ensure that the soil will be moistened throughout the root zone. Light sprinklings every day merely tend to wet the surface and encourage shallow root growth. Drip or trickle irrigation is encouraged as a method for conserving water. Use of organic materials as soil conditioners and fertilizers tends to improve the ability of the soil to retain moisture. Also, a good garden mulch will conserve soil moisture. Please observe all local watering regulations.

MULCHING

A mulch is any material, usually organic, which is placed on the soil surface around the plants. Organic materials most commonly used for mulching are leaves, grass clippings, pine straw, sawdust and wood shavings. Synthetic materials such as plastic sheeting have been used quite often in recent years. Among the benefits of a mulch are (a) conserves soil moisture, (b) conserves nutrients, (c) reduces soil erosion, (d) reduces crop loss due to nematodes, (e) reduces weed growth, (f) provides barrier between fruit and soil, thus reducing soil rot on fruit and (g) moderates the soil temperature.

Apply mulch before or after seeding or transplanting. Roll back the mulch with a rake in order to wet the soil beneath when irrigating, for best results. At the end of the garden season, the mulch (except plastic) may be removed and composted, or cut into the garden soil. Most mulch is woody and should have manure or other rich organic fertilizer applied with it when cutting into the soil.

WEED CONTROL

The primary purpose of cultivation is to control weeds. Weeds are easy to control when they are small. Shallow cultivation and hoeing are advised in order to reduce damage to the root system. A garden mulch, such as pine straw, leaves or other material, will help to keep weeds from growing if the mulch is thick enough to exclude light.

INSECT AND DISEASE CONTROL

During periods when infestations of various garden pests are high, control by natural means becomes very difficult. However, the following practices will help to reduce losses without use of chemical pesticides.

Plant resistant varieties.
Plant seed from disease-free plants.
Select pest-free transplants.
For cutworms, place a cardboard of tinfoil collar around plant stems at ground level.
Spade garden early so vegetation has time to rot before planting.
Use a mulch; vegetables touching the soil may rot.
Clean up crop refuse early.
Plant as early in the spring as practical.
Keep out weeds which harbor insects and diseases.
Summer fallowing (clean cultivation) helps control nematodes.
Summer flooding, where soil type permits, helps control nematodes.
Hand-pick insects.
Water in morning so plants are not wet at night.
Dispose of severely diseased plants before they contaminate others.
Some insects, such as cabbage worms, may be killed by spraying with natural preparations such as Bacillus thuringiensis.
Rotate garden areas
Bake transplanting soil in oven at 160 degrees F for 1 hour.
Crotolaria spectabalis and marigolds, when planted as cover crops, tend to reduce some kinds of nematodes. The use of marigolds to repel nematodes from interplanted vegetables is not effective control.
A good garden mulch tends to reduce damage caused by nematodes.
Many organic gardeners approve of and use sprays and other preparations containing naturally occurring materials. Diatomaceous Earth comes from petrified sea life. Pyrethrin, rotenone and ryania are examples of natural poisons from plant parts. These give some control to some insects under certain conditions.
Natural predators should be encouraged wherever possible; however, predators raised in captivity and then released into the garden area are usually ineffective.
Insecticidal soaps made from fatty acids tend to work well for some insects under average conditions.
Insect traps, baited with phermone lures, work well in some instances. Many of these have sticky adhesives to catch insects.
Solar fumigation is effective in reducing some soil-borne problems such as nematodes.

ORGANIC GARDENING SUPPLIES

Suitable materials for growing vegetables the organically are not always easy to locate. The "conventional" garden supply centers carry many products, especially seeds and equipment, which may be used by the organic enthusiast. However, for the difficult-to-find items, the gardener may have to order from specialty businesses dealing in organic gardening supplies.

Adapted from James M. Stephens, Circular 375, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. 2001

Pesticides are poisonous! Read and follow all safety precautions on labels. Handle carefully and store in original containers out of reach of children, pets or livestock. Dispose of empty containers immediately, in a safe manner and place. Pesticides should never be stored with foods or in areas where people eat.

When trade names are used for identification, no product endorsement is implied, nor is discrimination intended against similar materials. Be sure that the pesticide you intend to use is registered for the state of use.

The user of this information assumes all risk for personal injury or property damage.

For more information, call the URI CE Gardening and Food Safety Hotline at 1-800-448-1011 or (401)874-2929 from outside Rhode Island; Monday-Thursday between 9 am and 2 pm.

University of Rhode Island Cooperative Extension provides equal program opportunities.