Soil Fertility 101
By: National Gardening Association Editors
Just as a good foundation is necessary to support a building, good soil is necessary to build a successful garden.
All soil is not alike. It differs in texture, fertility, and balance.
At one extreme is beach sand, with grains so large you can see the individual particles. Water runs right through it. Not much grows in sand. In direct sun, it gets so hot you can hardly walk on it in bare feet.
At the other extreme is clay, such as the red and gray clay found in many parts of the country. Clay is made up of tiny particles that turn into a gooey mess when wet and something like cracked brick when dry. It is slow to warm up in spring and water stands on it, meaning gardeners with clay soil get a late start in spring.
Every gardener wants loam, which is a mixture of particle sizes. It holds water and is easy to work.
All soils have one thing in common. You can improve them by adding large amounts of organic matter, that is, material that was once alive. Leaves, grass clippings, manure, and vegetable wastes from your kitchen are examples. These are best for the soil if they are mixed together and broken down into soil-like particles in a simple and natural process called composting.
Turned into the soil, organic matter breaks up clay particles. In sandy soils, it binds the grains together and retains moisture and fertility.
Under the ground, the roots of plants are busy with their own unique processes that turn materials in the soil into growth, flowers, and fruit. Light and water are essential for this process.
In the soil, plants particularly need supplies of:
Nitrogen, for green leafy growth;
Phosphorus, for strong roots and healthy fruit and seed formation; and
Potassium, for vigorous growth and disease resistance.
When you buy fertilizer, you will see a series of three numbers on the bag, something like 5-10-10. They stand for the percentages of nitrogen, phosphorous, and potassium in the bag. Vegetables and flower fertilizers are blends like 5-10-10 or 10-10-10. Lawn fertilizers have a higher first number because lawns need more nitrogen to promote foliage growth. Too much nitrogen in vegetable garden soil can promote the growth of foliage instead of the crop you want.