Building Healthy Soil
Part 3 of 6
Improving Soil Structure
Even very poor soil can be dramatically improved, and your efforts will be well rewarded. With their roots in healthy soil, your plants will be more vigorous and more productive.
Sand particles are large, irregularly shaped bits of rock. In sandy soil, large air spaces between the sand particles allow water to drain very quickly. Nutrients tend to drain away with the water, often before plants have a chance to absorb them. For this reason, sandy soils are usually nutrient-poor.
Sandy soil also has so much air in it that microbes consume organic matter very quickly. Because sandy soils usually contain very little clay or organic matter, they don’t have much of a crumb structure. The soil particles don’t stick together, even when they’re wet.
To improve sandy soil:
- Work in 3 to 4 inches of organic matter such as well-rotted manure or finished compost.
- Mulch around your plants with leaves, wood chips, bark, hay or straw. Mulch retains moisture and cools the soil.
- Add at least 2 inches of organic matter each year.
- Grow cover crops or green manures.
Clay particles are small and flat. They tend to pack together so tightly that there is hardly any pore space at all. When clay soils are wet, they are sticky and practically unworkable. They drain slowly and can stay waterlogged well into the spring. Once they finally dry out, they often become hard and cloddy, and the surface cracks into flat plates.
Lack of pore space means that clay soils are generally low in both organic matter and microbial activity. Plant roots are stunted because it is too hard for them to push their way through the soil. Foot traffic and garden equipment can cause compaction problems. Fortunately, most clay soils are rich in minerals which will become available to your plants once you improve the texture of the soil.
To improve clay soil:
- Work 2 to 3 inches of organic matter into the surface of the soil. Then add at least 1 inch more each year after that.
- Add the organic matter in the fall, if possible.
- Use permanent raised beds to improve drainage and keep foot traffic out of the growing area.
- Minimize tilling and spading.
Silty soils contain small irregularly shaped particles of weathered rock, which means they are usually quite dense and have relatively small pore spaces and poor drainage. They tend to be more fertile than either sandy or clayey soils.
To improve silty soil:
- Add at least 1 inch of organic matter each year.
- Concentrate on the top few inches of soil to avoid surface crusting.
- Avoid soil compaction by avoiding unnecessary tilling and walking on garden beds.
- Consider constructing raised beds.
An excerpt from the article “Building Healthy Soil“, by Kathy LaLiberte, courtesy of Gardener’s Supply Company.