Garden Soil Wash Test

A soil wash test is a basic gardeners soil test to determine your garden soil type.

I am often asked whether a wash test cannot be used by the home gardener to see what materials make up a given soil. A direct yes or no answer is not possible. Light sandy soils containing little clay are easy to check in this way. The heavier the soil, however, the less accurate a wash test will be. The difficulty lies in breaking the bond between the acid clay particle and its cluster of alkaline particles. However, I find that if two tablespoonfuls of sodium nitrate are added to the soil sample, some of the electrical charge holding clay and lime together can be neutralized.

To perform this garden soil test, use a half-gallon mason jar. If any other type of container is used, be sure it is round so the water and soil can be swirled around rapidly. Put half a cupful of soil into the jar and then half fill it with water. Pull down the top tightly and swirl the soil and water for half a minute. Allow this to settle and then swirl again. Repeat several times.

With each mixing, more and more coarse particles will drift to the bottom and more and more clay particles will drift to the top, with silt settling out between them. Some of the clay particles may not settle out for several days with this garden soil test: they are so fine they form a colloidal solution in water.

Interesting information on a soil can be uncovered with this soil test. For example, a soil which one gardener complained was always cracking and was so high in clay he couldn't work it, produced an entirely different picture when washed. It contained only about I5 per cent clay, but about 45 per cent silt. In this proportion, clay and silt particles intermeshed so completely that they worked like the cement in a concrete mixture. The addition of steamed cinders to this soil worked wonders with its texture.

In soil testing laboratories, where samples are dried and sieved into their component parts, a much more accurate reading is possible, but these soil tests are not necessarily of more value than the simple home-made wash test which gives a pretty good idea of the proportions of various soil ingredients. And for the home gardener a 'pretty good idea' using this garden soil test is all that you need.