What Is Soil Made Of?

There are three basic categories:

There are two ways to easily determine your type.

Squeeze Test: Make a moist but not muddy 1 inch/0.5 cm ball in your hand. Then rub it between your fingers. Then refer to the chart below.

*Silt is in between clay and sand. It is slippery when wet, but doesn’t compact like clay.

Jar Test: First, fill a clean mayonnaise or other similar jar about 2/3 full of clean water. Add your soil sample until there is only 1 in/0.5 cm air space at the top. Screw the lid tightly and shake vigorously until no clumps remain.

Place the jar down and wait about one minute for the sand to settle. Then mark the top of this layer on the outside of the jar. Then wait one hour more and mark the top of the next layer that forms—the silt. Finally, leave the jar for 24 hours and mark the top of the last layer to form—clay.

Roughly equal layers of sand, silt and clay is ideal. If you have this loamy mixture, you should still add organic matter such as compost, dried leaves, or dried grass, but you will not need as much as when you have predominantly sand or clay.

pH

pH is a measure of relative acidity or alkalinity, with 0 being highly acidic, 14 highly alkaline and 7 neutral. Most plants grow well in a pH range of 6.2 to 7.2.

Measure the pH of your soil either by taking a sample to your local university cooperative extension or by doing it yourself with a pH strip, solution or meter.

If your pH is below 6.2, it needs alkaline material such as lime. If it is above 7.2, it needs acid material such as pine needles or peat.

Note that some plants such as azaleas, rhododendron, camellias, ferns and conifers prefer a more acidic pH between 4 and 5. Others, such as sagebrush, beech and asparagus prefer a higher pH up to 8. If you are planting or managing a rose garden, learn everything you need to know about proper soil for roses.

How to Make It Perfect

Even if you have good texture and pH, your growing area needs some help to produce the best for you. If you are removing sod, carefully remove all grass or other pre-existing plant material to reduce seed infiltration. You should hand turn or roto-till the area to a depth of 12 in/31 cm, removing rocks and stones. This is difficult only in the first year, and is child’s play when you enrich the bed in subsequent years. Once this is done, add organic material to the growing area and till again to mix it thoroughly.

If you have loam to start, you need mix in only enough organic material to cover the growing area to a depth of 2 in/1 cm. House compost, rotted manure, shredded dried leaves, dried grass clippings, peat and old sawdust are good.

These organic materials improve structure and tilth—the ability to properly retain water, drain properly and allow air and helpful insects to circulate. Add them every year. They are not the same as adding a fertilizer, however. For example, organic-rich loam will attract earth worms whose castings add nitrogen to the soil, providing an indirect fertilization. But some plants may require periodic additions of particular compounds to maximize their growth.

For sand or clay, you will need much more organic matter to adjust to the ideal structure. This is best done with repeated applications of 2 in/1 cm layers which you till in. If you can begin this process many weeks before your growing season, all the better.

In clay, the soil binds into plate-like layers which compact. In sand the opposite is true; it's so porous that it retains little water or nutrients.

The organic matter you add binds to the clay particles or the sand grains, making better sized “clumps” for gardening. It also attracts microorganisms whose byproducts also bind to these particles to make it the right consistency.

Return from Soil Types to Gardening Advice