Published on 03/08/00

Great Garden Soils Don't Come Naturally

Vegetable plants grow best in a fertile, loamy soil that drains well. Sandy-loam soils, well supplied with organic matter, are easily worked and quite productive. Unfortunately, most Georgia gardens don't have such soils.

Very coarse, sandy soils dry out fast and are hard to keep fertile.

Clay soils are hard to work and usually stay wet until late spring. They're often red or reddish-brown and sticky when wet. They may be grayish where drainage is poor.

These soils tend to form a hard crust after a heavy rain. They become so compacted that the plant's roots can't get enough oxygen to grow. Both clay and sandy soils must be modified for successful vegetable gardening.

Water Drainage

You can't expect to produce good vegetables on poorly drained soils. In many gardens, improving subsurface drainage with tile lines isn't practical. So surface drainage is critical.

Grade the surface so excess water will run off promptly, but in a controlled way, to prevent erosion. Leveling will eliminate pockets and low spots where water tends to stand for a long time.

Adding organic matter to clay and clay-loam soils will improve drainage and aeration, too.

Another option for dealing with poor drainage is to grow the vegetables in raised beds or on planting ridges. However, it may be harder in raised beds to manage water properly during drought periods.

Moisture at Working

Don't get overanxious in early spring. Never till or spade the soil until it's dry enough to crumble when worked. Soils high in clay content are easily damaged if worked when wet.

Experienced gardeners often use the "squeeze" test to tell 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 crumbles when you open your hand, it's ready to work. If it stays in a tight ball, wait several days (if it doesn't rain) before spading or tilling.

Texture and Structure

Conditioners can improve the soil's aeration, drainage, moisture-holding capacity and tilth, or workability.

Common soil conditioners include compost, peat moss, composted animal manures, green manure crops and coarse sand.

By incorporating coarse, rather than fine, sand and organic matter into a garden soil, you can, over time, produce a desirable, loamy-type soil. However, adding fine sand to clay can produce something close to brick.

A common mistake when trying to improve the garden soil is failing to use enough conditioners. For chiefly clay or sandy soil, use large amounts to effectively improve texture and structure.

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


When you incorporate organic materials such as straw and shredded bark into the soil, you have to add extra nitrogen fertilizer.

The nitrogen provides extra nutrition for microbes decomposing the added organic matter. It prevents a temporary nitrogen deficiency in the vegetable plants.

Apply one-fourth pound of ammonium nitrate or ammonium sulfate for each bushel of mulch, or 2 pounds of a complete fertilizer such as 5-10-5, 8-8-8 or 12-12-12, per 100 square feet.

If you see any yellowing of lower foliage, or if garden plants lack vigor in early summer, apply more nitrogen.

Soil pH

Use a soil test to see if your soil needs limestone to adjust the pH. Most vegetables grow best in slightly acid soil with a pH of 6.0 to 6.8. You can get your soil pH-tested through the county Extension Service office or a private lab.

Remember, it took years to make the soil you have. It may take several years to improve it.

Wayne McLaurin is a professor emeritus of horticulture with the University of Georgia College of Agricultural and Environmental Sciences.