Improving Soils for Vegetable Gardening
HYG-1602-92 Marianne Riofrio E.C. Wittmeyer
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. Unfortunately, many gardens do not
contain such soils. 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
essential oxygen required for growth. Clay and sandy soils must be
modified for successful vegetable gardening. Basic Considerations 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. Another option for dealing with poor
drainage, is to grow the vegetables in raised beds or on planting ridges.
However, keep in mind that proper water management during periods of
drought may be more difficult in raised beds. See Home, Yard and Garden
fact sheet 1641-92 for more details on raised-bed gardening. 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. Experienced
gardeners often use the "squeeze" test to determine if the soil
is ready. With a spade, turn over a slice of soil about 6 inches deep.
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 freezing and thawing that takes place in the
winter. Fall-worked soils often require only leveling and a light raking
in the spring before planting. Be cautioned, however, that such
fall-worked soils can be compacted quite easily if worked 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, rather than fine sand, and organic matter into a
garden soil, the gardener can, over time, produce a desirable loamy-type
soil. The addition of fine sand to some soils, especially clay, however,
will be detrimental to the soil structure. A common mistake made when
attempting to improve garden soil is failing to use enough soil
conditioning materials. For chiefly clay or sandy soil, 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 rye or
ryegrass (or winter barley in southern Ohio). Rye is preferable for late
(after September 15) cover crops seedings. Cereal rye and barley are
seeded at a rate of 1/3 lb. per 100 sq. ft. of garden area. Ryegrass is a
suitable soil cover crop, but should be seeded before September 15 for
best results. It is seeded at a rate of 3 oz. per 100 sq. ft. or 1 and 1/2
to 2 lbs. per 1,000 sq. ft. Cover crops prevent soil erosion and add
organic matter when turned under in the spring. However, such crops should
be turned over before growth is so tall they are difficult to handle.
Cover crops may be seeded between garden rows in August through September,
even if vegetables are not yet 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. Contact your local Cooperative Extension office for information on
getting your soil pH tested. The authors gratefully acknowledge James D.
Utzinger and William M. Brooks for their 1983 fact sheet on which this is
based.
All educational programs conducted by Ohio State University Extension
are available to clientele on a nondiscriminatory basis without regard to
race, color, creed, religion, sexual orientation, national origin, gender,
age, disability or Vietnam-era veteran status.
Keith L. Smith, Associate Vice President for Ag. Adm. and
Director,
OSU Extension. TDD No. 800-589-8292 (Ohio only) or 614-292-1868
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