Growing Vegetables Organically (B 1011)Download PDF
- Garden Location
- Garden Planning
- Soil Preparation
- Green Manures
- Soil Solarization
- Starter Solutions for Transplants
- Successive Planting and Crop Rotation
- Crop and Variety Selection
- Insect and Disease Control
Growing vegetables organically can be rewarding and productive. This publication explains the basic elements of successful organic vegetable production, from initial site location, soil preparation, irrigation and variety selection to insect and disease control, composting, mulching and fertilization, and successive planting and crop rotation.
Planting your vegetable garden in the right location will help ensure the best production. The garden should have a southern exposure, such as on the south side of your home, or be located in an open field if at all possible. The chosen location should receive a minimum of 6 to 8 hours of direct sunlight every day. It is also important to have a water supply nearby. For convenience, a location near the house is desirable. A site that drains well even after a heavy rain is ideal. Poor drainage may be improved by re-grading, digging ditches, installing a tile drain field or building raised beds.
Nearby trees and shrubs may have extensive root systems that can interfere with water and nutrient uptake of plants at your site. Locate the garden away from these areas to minimize or avoid this problem. As a last resort, consider removing trees and shrubs that may interfere with production.
Land with a slope of 1.5 percent or greater (an 18-inch elevation change in 100 feet) should be avoided or terraced to prevent runoff and soil erosion. Contour planting, or setting the rows to follow the contour of the land, can also help with runoff problems. Ask your local county Extension agent for more information on dealing with this situation.
Sites with serious weed problems such as nutsedge, Bermudagrass or kudzu should be avoided unless adequate measures are taken to control them. The presence of these weeds does not preclude you from using a site, but considerable work is required to remove and control these weeds.
Consider fencing the site if you have a significant wild animal population nearby. Deer, raccoons and rabbits, to name a few, may become problems. Domestic animals such as dogs may also become a problem because many like to dig. Fences as high as 6 feet, an electric fence or some combination may be required to control animals such as deer.
Not all of the above recommendations can be accommodated in all situations. Many established neighborhoods have large shade trees and extensive landscaping. This may preclude having a large row garden, but container gardens may still be possible in places where they can be moved to sunny locations as needed. Growing leafy greens is possible in a less-than-ideal light situation, but they will require some full sun during the day.
The size of your garden will partly determine many aspects of your garden plan. Large gardens where tractors will be used can be worked more easily with long rows; small gardens may be worked more easily in small beds with footpaths surrounding them.
There are many things to consider when planning your garden. Fertility requirements vary by crop, so heavy feeders and light feeders can be grouped separately to help manage fertilization. Long-season crops such as eggplant, tomato, pepper and okra should be planted so they don't interfere with replanting short-season crops such as beans and lettuce. Tall-growing crops such as pole beans, tomatoes and corn should be planted so they don't shade shorter crops. You may not be able to accommodate all of these recommendations in your garden, but incorporating as many as possible will help ensure success.
An important part of garden planning is record keeping. General information about soil amendments used and weather information (particularly rainfall and first and last frost dates) can be useful, especially when tracked from year to year. Specific information about a particular vegetable can also be helpful for future planning. Information such as variety selection, planting date, days to harvest, and disease and insect problems should be noted. This data can help you determine which vegetables and varieties are best for your location. Watering, fertilizing and any cultural practices should also be recorded. This helps determine what should be done in the garden from day to day. Finally, keep track of what is grown where in your garden. This information will help with successive plantings and crop rotation.
When to plant is also an important part of garden planning. Table 6 lists the hardiness and days to maturity for several vegetables. Vegetables can be classed into two broad categories: warm- and coolseason crops. Warm-season crops can be further subdivided into tender and very tender vegetables, and cool-season crops can be subdivided into hardy and half-hardy crops. Very tender crops cannot stand any frost and will not do well under cool nighttime temperatures (below 55°F). Tender crops also don't like frost but can stand cooler night temperatures. Hardy cool-season vegetables can withstand frost and can be grown during the winter in all but the coldest northern parts of Georgia. Half-hardy cool-season vegetables can withstand cool temperatures and light frosts, but hard freezes and heavy frost can be detrimental.
Growing a crop without irrigation is possible, but irrigating will enhance your success. Several different irrigation methods can be used, although overhead and trickle irrigation are the most common.
Trickle irrigation is the most water-use efficient because water is delivered directly to plant roots via a low-volume soaker hose, drip tape or emitters. There are some disadvantages to trickle irrigation, including installation and maintenance costs. These types of systems may need to be monitored more closely, especially with newly transplanted plants, because they may not wet the soil sufficiently or evenly for new plants. Drip irrigation tape or soaker hose placement may have to be adjusted, particularly during plant establishment.
Overhead sprinkler systems are easy to use and require less maintenance and monitoring; however, they can result in uneven water application and use water inefficiently. For more detailed information on irrigation see Irrigation for Lawns and Gardens, Bulletin 894 from the University of Georgia Cooperative Extension.
Organic gardening requires a long-term outlook with respect to soil preparation. In fact, the key to successful organic gardening is to feed the soil with organic matter, which feeds the plant, rather than to feed the plant with inorganic fertilizer as in conventional production. An ideal soil has equal parts sand (0.02 to 2.0 millimeters), silt (0.002 to 0.02 millimeters) and clay (0 to 0.002 millimeters), and contains about 5 percent organic matter. Most mineral soils in Georgia will have less than 1 percent organic matter and are rarely ideal. However, with work, most soils can be improved and made productive.
Because it takes a long-term outlook to build a good soil, don't be disappointed if your results are less than ideal the first year or two. New sites should have all plant matter removed or turned under. Areas with Bermuda sods or other invasive plants should have the plants removed to the compost pile (see "Composting" in this publication) and the soil turned under to expose roots and rhizomes to desiccation. In addition, soil solarization (see "Soil Solarization" in this publication) can help manage these hard-to-control weeds.
Some soils may have hardpans, which are impervious layers several inches under the soil. These hardpans are often found on old farmland or new home sites where equipment has compacted the soil. In either case, these hardpans must be broken up. On clay soils this can be very difficult.
Soils should be turned to 10 to 12 inches deep. One method is to double dig the garden. To do this, dig a trench 6 to 8 inches deep along one side of the garden, placing the soil on the outside edge. Then use a spade or garden fork to loosen the soil 6 inches deep at the bottom of the trench. Soil on the inside edge of the trench is moved to fill the existing trench, creating a new trench in its place. With a spade orgarden fork, loosen the soil in the bottom of this trench to a 6-inch depth. Continue in this fashion until the entire garden has been double dug. The soil from the first trench can then be moved into the last trench. This method of garden preparation will leave a deeply turned soil but is very labor intensive. Alternatives include using equipment such as tractor-mounted plows or a Rototiller set to the deepest depth. Organic matter should be added during this deep-turning process.
Organic matter in soil is important for two reasons. First, as it breaks down it releases nutrients that crops can utilize, and second, it improves the water- and nutrient-holding capacity of the soil. The amount of organic matter to add varies with the chosen material, the type of soil and weather conditions. On sandy soils in tropical and subtropical regions, as much as 2,300 to 4,600 pounds per 1,000 square feet may be required to gain a benefit from the addition of organic matter. On heavier soils in regions with cooler climates and less rainfall, as little as 200 pounds per 1,000 square feet may be sufficient.
As an example, an acre of dry soil 6 inches deep weighs about 2 million pounds, which means that 1,000 square feet of soil to the same depth weighs approximately 46,000 pounds. If you wished to raise the organic matter of this soil 1 percent, you would have to add 460 pounds of organic matter. The amount of material required may actually be quite a bit more because most organic sources have a high water content – as much as 50 percent or more. In addition, many organic sources have high ash (nonorganic residues) content – as high as 25 percent or more. Organic matter with 50 percent water content and 25 percent ash would require 1,840 pounds applied to 1,000 square feet to raise the organic fraction of the soil 1 percent. This may be impractical both in terms of obtaining the necessary organic matter and the fact that organic matter must be added each year to sustain the increase; however, low rates (200 pounds per 1,000 square feet of organic matter) can have a noticeable improvement in soil tilth. Additions of 500 to 1,000 pounds of organic matter per 1,000 square feet per year can have a beneficial effect on soil tilth and plant growth. Table 1 lists the minimum amounts of several types of organic matter that should be added to the soil. It is highly recommended that you have the organic matter tested for its nutrient content so that application rates can be adjusted accordingly and because fresh material can damage plants and be hazardous to the environment through runoff. In all cases, fresh material should be composted to kill harmful pathogens and weed seed.
Compost is an excellent source of organic material for your garden. If you make it yourself, it has the added benefit of reducing the amount of waste your household generates. All organic kitchen and garden waste except animal products can be composted. Material such as bones and animal scraps should be avoided because they attract vermin, flies and scavenging animals. A convenient size for a compost pile is 4 feet wide by 5 feet long by 5 feet high. A frame made of pressure-treated lumber can be built to hold the compost, and containers specifically designed for composting can be purchased, including types that can be easily tumbled.
If you build your own compost pile, begin the compost by adding 12 inches of organic matter (kitchen scraps, yard waste, etc.) and applying 1 to 2 pounds of high-nitrogen organic fertilizer such as dried blood, guano or poultry manure. Finally, add 2 inches of soil. Continue building the compost pile in this layered fashion as you generate organic matter. Another method of composting is to combine 65 percent "brown" material with 35 percent "green" material. "Brown" materials include tree and shrub trimmings and raked leaves, while "green" materials include grass clippings and kitchen scraps. "Brown" materials such as tree and shrub trimmings should be chipped prior to use. For complete and rapid decomposition, the compost pile should be turned regularly, particularly during the initial stages. The center of the pile should be concave to hold rainwater and should begin to heat up within a couple of weeks. The composting process should be complete within two to three months, depending on materials and outside temperature.
Large material such as tree limbs and corn stalks should be chopped into smaller pieces to facilitate decomposition. Some materials, such as lawn clippings, will decompose very rapidly; others will require turning the compost pile and adding more high-nitrogen organic fertilizer. This will restart the heating and decomposition process.
If you use materials from outside sources (e.g., pasture hay or straw), you should check to make sure no persistent herbicides have been applied. Herbicides such as picloram (Grazon®) are extremely persistent and will damage your plants.
Any crop grown on land with the intent of turning it into the soil is called a green manure. Generally, legumes and various grasses are grown as green manure. Turning under a crop can provide a number of benefits, including increasing organic matter of the soil, decreasing certain disease problems and increasing the nutrient level in the soil. After the green manure is turned under, it decomposes and adds nutrients and organic matter to the soil.
When used as a green manure, grasses and small grains can decrease the incidence of nematodes, which are microscopic worms that feed on certain plant roots, weakening the plants.
Using various legume crops can increase the amount of nitrogen in the soil. The amount of nitrogen will depend on the crop, the time of year and when in the crop cycle the plants are turned under. Anywhere from 30 to 125 pounds of nitrogen may be added to the soil when a legume crop is turned under. Table 2 lists several crops that can be used as green manures.
Difficult-to-control weeds and soilborne pathogens may be controlled with soil solarization, which involves covering the soil surface with clear plastic for eight to 12 weeks or longer. Clear plastic is used because most of the light energy is transferred to the soil. Black plastic absorbs a lot of heat, but it also shades the soil and is not as effective as clear plastic.
In temperate regions where there can be a significant number of overcast days, soil solarization may require an entire season to be effective. For best results, solarization should extend over the entire summer. Although an entire growing season may be lost, weed and soilborne pathogen control will carry over to the following season. This can be particularly effective when done prior to winter vegetable production.
To begin with, all plant material and crop residue, as is practical, should be removed. The soil should be turned to break up any clods and raked smooth. The area should be watered thoroughly so the soil is saturated. The area then should be covered with a clear plastic sheet 1 to 4 millimeters thick. The sheet can be secured along the edges with soil or rocks. Soil solarization works best during the summer months when air temperatures are high and sunlight is most intense. Soil solarization is not effective during extended periods of cool temperatures or overcast weather.
Starter solutions can help get transplants and newly emerged seedlings off to a good start. High phosphorus is particularly important in these solutions because it encourages root growth; however, high-phosphorus organic fertilizers may not be readily available. Water-soluble fertilizers such as fish emulsion can also help plants get off to a good start. This material should be mixed with water at a rate of 2 to 4 tablespoons per gallon and applied to newly set transplants. Apply ½ to 1 pint of this solution to each plant.
In the past, manure teas were recommended as a starter solution. This practice should be abandoned because of the possibility of transmitting human pathogens.
Because of the relatively long growing season in Georgia (particularly south Georgia), it is possible to produce more than one crop a year on the same land. Planting a second or third crop on the same land within the same growing season is called successive cropping or double cropping. Crop rotation, on the other hand, refers to planting different vegetables on the same land from year to year. Related vegetables should not be planted on the same land in succession or rotation. For example, squash should not be followed by a related vegetable, such as watermelon, cantaloupe or cucumber. This practice helps minimize soilborne disease problems and helps maintain soil fertility. Table 3 lists related vegetables.
One of the most important decisions an organic grower makes is crop and variety selection. Not all vegetables do well in all locations. Vegetables commonly grown in your area are your best bet for success. Trial and error will also help determine which vegetables are best suited to your area. As you try different varieties, keep records so that this information can be used in planning subsequent years. Climate, disease and insect problems will be important criteria when selecting vegetable crops. It should be pointed out, however, that one year's results may not be enough to determine the success of a particular vegetable. For example, a mild winter may result in a greater insect problem than you might expect the following season. On the other hand, a cold winter may result in sufficient suppression of the insect to make for a successful year.
Variety selection is another important consideration. When available, varieties with disease and insect resistance are best. Resistance, however, is seldom 100 percent, and the plant may show less severe symptoms than susceptible varieties.
Varieties can be grouped into two broad categories based on how they were developed. F1 hybrids are developed from crossing lines that have been inbred for several generations. These varieties have advantages of increased uniformity and, often, increased yield compared with open-pollinated varieties. The disadvantage of these varieties is that the seeds are more costly and seeds saved from hybrids don't come true-to-type. Their performance will be more varied and perhaps noticeably worse. In addition, seed companies are constantly changing F1 hybrid varieties. Not all vegetables lend themselves to F1 production. For example, because of the low amount of seed produced from each cross, beans and peas are not available as F1 hybrids.
Open-pollinated varieties are less expensive, and popular open-pollinated varieties will remain on the market for years. In addition, these seed will remain true-to-type from one year to the next. Most older varieties are open-pollinated types. Very old varieties are often referred to as heirloom varieties, and many can be dated to the previous century and beyond. These varieties are often sources of unusual colors, shapes and flavors.
Several vegetables, including sweet-potatoes and Irish potatoes, are reproduced vegetatively; that is, from parts of the plant itself. To improve your results with these crops, buy certified slips for sweet-potatoes and seed pieces for Irish potatoes. The certification process ensures true-to-type, disease-free material.
Mulching serves several purposes in organic production, including reducing weed growth, conserving soil moisture and nutrients, regulating soil temperature, helping prevent soil erosion and limit water splashing on plants (which keeps them cleaner and reduces the spread of disease). An added benefit comes from organic mulch: As it decomposes, it increases the amount of organic matter in the soil. Almost any organic matter can be used successfully as mulch, including hay, straw, leaves, pinestraw or bark. Avoid materials that may have a lot of seed such as overgrown grass clippings. Fresh material, particularly sawdust, should be avoided because it can rob your soil (and thus your plants) of nitrogen. In addition, avoid organic material that may be contaminated with toxic chemicals or herbicides because these may damage your plants. Pastures are often treated with herbicides that can injure plants when mulch is used from such sources. Some herbicides, such as picloram (Grazon®), can even survive the composting process.
Mulches should not be applied too early in the spring because this can delay soil warming. Wait until the soil is 65°F to a depth of 4 inches before applying. Solid materials such as newspapers should be weighted with soil to prevent them from blowing away. Weed control with mulches may require the continual addition of new material to smother weeds as they emerge. Keep all mulches 2 to 3 inches away from the stems of plants.
You must have accurate information about your soil to fertilize properly. The soil pH is important in determining nutrient availability to the crop. Optimum pH for most vegetables is between 6.0 and 6.5. Soil testing is the only accurate method of determining the soil pH. Such tests will offer recommendations on the amount of lime to apply if the soil pH is too low. Approximately 1 ton of lime is required to raise the pH of an acre 1 point; this is about 5 pounds per 100 square feet. The actual amount of lime required, however, will vary based on soil texture, the crop grown and the soil's buffering capacity. In order to determine proper fertilization, it is important to know the soil's nutrient status, which a soil test will provide. To illustrate (using Tables 4 and 8), assume you are planting only heavy feeders in your garden and plan to use Fertrell Super as an organic fertilizer. Heavy feeders require 3 pounds of nitrogen per 1,000 square feet (Table 4). Fertrell Super contains 4 percent nitrogen (Table 8). Convert 4 percent nitrogen to its decimal equivalent by dividing 4 by 100 to get 0.04. Calculate the pounds of Fertrell Super required to provide 3 pounds of nitrogen by dividing 3 by 0.04 to get 75 pounds. If your garden is smaller or larger than 1,000 square feet, adjust the amount accordingly.
Most organic fertilizers are relatively low in nutrients that are usually of low solubility. In addition, since plants require nutrients in their simple ionic form, these nutrients must undergo a process of mineralization to become available for plants to use. This means that organic growers need to plan ahead concerning their fertility needs. Organic fertilizers generally will have to be applied earlier than conventional fertilizers and may have to be applied in greater quantities. Applications of organic materials such as manures and compost are not necessarily added to soils as fertilizers, but rather improve soil characteristics such as water and nutrient holding ability.
The best first-line method of reducing insect and disease pressure is to use resistant varieties when available. A good example is VFN tomatoes, where the VFN stands for Verticillium-, Fusarium- and nematode-resistance. Your local county Extension office or seed supplier will have the latest information on available resistant varieties.
Keep the garden as free of diseases as possible. Plants with disease symptoms should be removed and destroyed. A properly constructed compost pile, which should heat up in the center, can control many diseases.
Keeping your plants dry will help reduce disease pressure. Using trickle irrigation rather than overhead sprinklers will reduce the amount of time plants remain wet and also conserve water. Of course, there's nothing we can do about the rain.
Crop rotation also can be an important method of controlling some but not all soilborne diseases. Proper crop rotation can substantially reduce nematodes in the soil but will do little to reduce Southern blight.
Insect control begins with healthy plants. Don't bring problems into your garden; buy insect-free transplants. Timing is also important. Insect populations tend to increase as the season progresses, so planting early can avoid many insect problems. Encourage beneficial insects to stay in your garden. This can be as easy as nailing a horizontal board to a fence to encourage wasps to build a nest.
Finally, there are many organically acceptable products that can be applied to your crops. Check with your local county Extension agent, who can give you the latest information on these products.
Table 1.Amount of organic matter to add from various sources.
Table 2. Green manure crops, season of growth, amount of seed and type.
Table 3. Vegetables in related groups or families.
Table 4. Comparison of fertilizer needs for heavy, medium and light feeders with a medium soil test for phosphorus and potassium in pounds per 1,000 square feet of actual nutrient (nitrogen, phosphorus or potassium).
Table 5. List of vegetables based on whether they are light, medium or heavy feeders.
Table 6.Vegetable hardiness and days to maturity.
Table 7.Recommended vegetable varieties for Georgia.
Table 8. Guide to the mineral nutrient value of organic materials.