Sandy soils, those with 85% to 90% sand-sized particles, can be difficult to manage. They don’t hold water well and they are not very fertile. Excessively sandy soils are characteristically gritty to the touch. Their large pores make it just as easy for water to run out as in. Nutrients also easily slip in and out of sandy soils.
On the plus side, these soils are not prone to erosion by water, since the water goes right through them. But they can be easily eroded by wind, depending on their location and prevailing winds. Sandy soils are easy to cultivate. They don’t get too wet and they don’t get sticky like heavy, clay soils. They can be worked right after a rain without difficulty, and they can be worked when they are dry.
Managing Sandy Soil
Because sandy soil doesn’t hold on to either water or mineral nutrients very well, it’s important to apply them frequently. Check the soil often and water as soon as it is just barely moist. It can go from moist to very dry quickly, so be alert. Farmers call this type of soil “droughty”.
Sandy soil absorbs water quickly, so runoff is seldom a problem. Because it drains so quickly, letting ample air into the soil, overwatering is seldom a problem either.
But here’s a caveat: a few sandy soils have just the right mixture of silt-sized particles to have very low porosity. The silt plugs up the pores between sand particles so water doesn’t enter it quickly, and it has drainage problems. This soil is extremely dense but, because it doesn’t contain clay, has no structure to speak of. Handle it as you would any other sandy soil, by adding organic matter. In a short time, the organic matter will open the soil and improve drainage. In the meantime, apply water slowly to avoid puddling.
Soluble fertilizers wash out of sandy soil quickly, so it’s important to use slow-release fertilizers. Look for fertilizers with large percentages (more than 50% of the nitrogen) of water-insoluble nitrogen (WIN). Nitrogen in water-insoluble forms must be acted on by soil bacteria before it is available to plants. This takes a while, so the nutrients are released over a period of weeks instead of all at once.
Some plants have evolved on sandy soils, and are able to cope with dry periods without being harmed. Select plants that are suited to the soil you have as well as the climate you live in.
Improving Sandy Soil
Adding organic matter—or clay and organic matter—to sandy soils is the only way to increase their ability to retain water and nutrients.
The organic matter is decomposed by soil bacteria into humus, a soft, sticky material that holds both water and nutrients like a sponge.
Humus is more effective in the presence of clay. If your soil has very little clay content, add some at the same time as the organic matter. Mix in about one inch of clay soil one time only. You don’t need to add it often, as you do with organic matter.
Add organic matter as often as you can. Work in 1 to 4 inches every time you till a vegetable garden or annual bed, or prepare soil for planting. Keep a mulch of organic matter under trees, shrubs, and perennial flowers. Earthworms and insects will work it into the soil for you.
Compost, peat moss, well-rotted manure, or other easily available organic matter are good choices for working into sandy soils or for mulches.
Mulches that decompose slowly, like bark chunks, will help somewhat, but their action is slow. Rapidly-decomposing mulches like compost and manure are more effective at improving the soil.