Vegetable plants grow best in a fertile, well-drained soil of loamy texture. Sandy loam soils, well-supplied with organic matter, are easily worked and are quite productive. Very coarse, sandy soils dry out rapidly and are difficult to maintain at a high level of fertility. Clay soils are hard to work and usually remain wet until late in the spring. These soils are often yellow or dark brown and sticky when wet, or grayish in color where drainage is poor. Clay soils tend to form a hard crust after a heavy rain and become so compacted that the plant's root system is deprived of the oxygen required for growth. Clay and sandy soils must be modified for successful vegetable gardening.

To obtain a desirable soil for gardening, consider the following areas of concern: water drainage, moisture condition at the time of working, erosion, texture and structure, fertility and pH (acidity or alkalinity).

Water Drainage:

Satisfactory vegetable production cannot be expected on poorly-drained soils. Where drainage problems exist, and where an outlet is available, four-inch drain tile in lines 25 feet apart is suggested. The tile should be at least 2 feet deep. The fall in the lines will depend on the outlet and length of lines, but water needs a fall of at least 2 inches per 100 feet of line.

In many home gardens, improving subsurface drainage with tile lines is not practical. Therefore, surface drainage is very important. The surface should be graded so that excess water will be removed promptly, but in a controlled manner to prevent erosion. Leveling will eliminate pockets and low spots where water tends to stand for long periods. Adding organic matter to clay and clay-loam soils will also improve drainage and aeration.

Growing vegetables in raised beds or on planting ridges is another option for controlling drainage. However, keep in mind that proper water management during periods of drought may be more difficult in raised beds.

Moisture Conditions at Time of Working:

Many anxious gardeners work the soil in early spring when it is still too wet. The soil should not be tilled or spaded until it is sufficiently dry to crumble when worked Use the "squeeze" test to determine if the soil is ready: use a spade to turn over a slice of soil about 6 inches deep, then pick up a handful of soil and squeeze it. If the soil remains in a tight ball when pressure is released, wait several days (without rainfall) before spading or tilling. If the soil crumbles when pressure is released, it is ready for working. Soils high in clay content are easily damaged if worked when wet.

Erosion:

Some clay soils benefit from fall tilling or spading. Such soils will be loose and fluffy in the spring as a result of the conditioning effect of winter freezing and thawing. Fall-worked soils often require only leveling and a light raking in the spring before planting. Fall-worked soils can be compacted quite easily, however, if worked when too wet.

Texture and Structure:

Soil texture and structure can be modified by using soil conditioners. Soil conditioners act to improve soil aeration, drainage, moisture-holding capacity and tilth, or workability, of the soil. Commonly used soil conditioners include compost, peat moss, sawdust, wood chips, composted animal manures, green manure crops, coarse sand and perlite. By incorporating coarse sand and organic matter into a garden soil, the gardener can, over time, produce a desirable loamy-type soil. The addition of fine sand, however, into some soils, especially clay, will be detrimental to the soil structure.

A common mistake made when attempting to improve garden soil is failing to use enough soil conditioning material. For soil which is mostly clay or sand, large amounts of conditioners must be used to effectively improve texture and structure.

Condition the soil by applying 3 to 4 inches of organic matter and, if available, 1 to 2 inches of coarse sand uniformly over the surface of the garden. Till or spade the material thoroughly into the top 8 to 10 inches of soil.

Avoid Temporary Nitrogen Deficiency:

Organic materials such as straw, fresh sawdust, wood chips, and shredded bark require the addition of nitrogen fertilizer when they are incorporated into the soil. The nitrogen provides extra nutrition for microbes decomposing the added organic matter, preventing a temporary nitrogen deficiency in the vegetable plants.

Apply 1/4 lb. of ammonium nitrate or ammonium sulfate for each bushel of mulch material, or 2 lbs. per 100 sq. ft. of a complete fertilizer such as 5-10-5, 8-8-8, 12-12-12 or similar analysis. If there is any yellowing of the lower foliage and garden plants lack vigor during early summer, apply additional nitrogen fertilizer.

Use of Cover Crops:

Garden soils benefit by being protected by a winter crop such as winter rye. Winter rye is preferable for late (after September 15) cover crops seedings and is seeded at a rate of 1/3 lb. per 100 sq. ft. of garden area.

Cover crops prevent soil erosion and add organic matter when turned under in the spring. Cover crops should be turned over before growth is so tall they are difficult to handle. Cover crops may be seeded in August or September between garden rows before vegetables are harvested.

Soil pH:

A soil test should be made to determine if limestone is needed to adjust the pH of the soil. Most vegetables grow best under slightly acid conditions with a pH of 6.0 to 6.8. See GreenShare Factsheet on soil testing for more information.

Adapted from Marianne Riofrio and E.C. Wittmeyer, Ohio State University Extension, 2000