Adapted from Rhoda Burrows and David Graper, South Dakota State University
Good soil preparation is essential for growing vegetable crops. Plow or spade, depending on available equipment and garden size, in either the fall or spring. Work the soil about 8 inches deep. Avoid working the soil when it is too wet because this will cause compaction and clods.
A soil organic matter content of 5 percent, as indicated by a soil test, is generally considered ideal. For most soils, better crops can be produced if high- quality organic matter (OM) is added. Organic matter benefits the soil by:
- -Supporting valuable soil organisms
- -Improving soil texture
- -Increasing water-holding capacity
- -Providing aeration and better drainage
- -Making fertility more effective
Organic Matter Sources
The most commonly used vegetable garden organic matter sources are described below.
Animal manure provides organic matter and many nutrients. Apply in the fall and work the manure into the soil. Because fresh animal manures can damage plants and may also contain potentially harmful pathogens or weed seeds, it is best to use old, well-rotted manure or prepackaged or composted manures. Waste from pets or carnivorous (meat eating) animals is not recommended.
If you apply manure, be sure it has been aged at least six months at warm (growing season) temperatures. This aging process will help eliminate most of all potential human pathogens that may be transmitted through animal feces. The aging process will also help decrease potentially high salt levels in the manure, so you are less likely to observe "burning" or other salt damage on you plants. Aging the manure also will decrease the number of remaining viable weeds seeds.
For more information, see:
Green Manure refers to cover crops such as ryegrass, vetch, alfalfa, etc., that are turned under to decompose. With nonleguminous crops such as rye or oats, nitrogen added at plowing time will help decompose the material and prevent nitrogen starvation in the succeeding crop.
Cover crops generally are planted near the final harvest. If enough growth takes place, the cover crop can be plowed down in the fall; however, this may also be done in the spring. One advantage of waiting until spring is that the cover crop can hold additional snow during the winter months, which helps retain soil moisture, insulate perennial plants, and prevents soil erosion from winter winds.
Compost consists of plant refuse placed in a pile or bin with small amounts of soil and fertilizer to decompose. Compost makes a good substitute for animal manure for improving soil structure and water-holding capacity. It will also add nutrients, but it has much lower levels of nitrogen, phosphorous, and potassium compared to manure.
For more information, see:
Most vegetables prefer a slightly acidic soil pH within the range of 6.0-7.0. Figure 1 shows soil pH preferences for common vegetables. If the soil is too acidic or alkaline, certain nutrients become unavailable to the plant and poor growth or death of the plant results. The pH of a soil can be learned from taking a soil test.
There are ways to alter pH. The most common, lime, is used to raise the soil pH when it is too low (acidic). Elemental sulfur is the most effective material for lowering soil pH if it is too high (alkaline). Since both of these materials take time to react with the soil, they are best incorporated into the soil at a depth of 6 inches well before planting time, six months to a year if possible.
If soil test results indicate the soil pH is not suitable for vegetable growth, follow the soil test recommendations for modifying pH. For more information on soil testing and raising and lowering soil pH, see the following articles:
The best time to fertilize the entire garden is before planting so nutrients can be worked into the soil. Vegetables need a well-balanced diet. For best growth, nitrogen, phosphorus, and potassium and other micronutrients in adequate amounts must be available for uptake by plants. It is often necessary to rely on fertilizer to provide at least part of the nutrient requirements of garden plants. Proper fertilizer applications to vegetable crops may return more money for less cost than any other expenditure.
Organic fertilizers such as fish emulsion, manures, and blood meal are alternatives to chemical-based fertilizers. Except for manures and fish fertilizers, organic materials tend to be low in phosphorus.
Materials such as decomposed straw, leaves, or grass clippings will not provide a sufficient balance of plant nutrients. Also, as fresh organic matter initially breaks down, it may temporarily deplete the soil of available nitrogen.
If you purchase fertilizer, check the label. Some are applied as granules, and others are dissolved in water prior to application. By law, all commercial fertilizers must list the contents expressed as a percent of each nutrient in the material. For example, an 8-32-16 NPK fertilizer will have:
- -Nitrogen (N) = 8%
- -Phosphate (P205) = 32%
- -Potash (K20) = 16%
For more information on fertilizers, see:
Certain nutrients are needed in all vegetable plantings, but fertilizer should be used according to the needs of each plant. Improper or excessive fertilization, especially with nitrogen, can cause excessive vegetative growth and reduce yields of fruiting vegetables. Call your local Extension office for information on taking a soil test to determine proper application rates.
Although the best time to fertilize the entire garden is before planting, once vegetables are up and growing, they may be side-dressed with a nitrogen fertilizer if a soil test indicated a need. A good lawn fertilizer containing no weed killers or seed germination inhibitors, but 20 to 30 percent nitrogen works well. Stay 6 to 8 inches away from the main stem in the case of tomatoes and 3 to 4 inches away from onions.
Leafy crops such as lettuce, spinach, cabbage, and sweet corn may be side-dressed after they have developed three to five true leaves. Use about 1 cup for each 25 feet of row, worked into the top 2 inches of soil, along each side of the row.
Wait to side-dress fruiting vegetables such as tomatoes, peppers, eggplant, squash, pumpkin, or cucumbers until after the plants have begun to set fruit. Fertilizing too early can reduce or even prevent fruit set.