How organic matter improves the soil: Organic matter incorporated into clay or compacted soil opens up the soil, giving it a crumbly structure. This reduces stickiness, improves drainage, and allows air to move more easily into the soil. In sandy soil, organic matter acts as a sponge, holding moisture and nutrients in the root zone. The quantity of organic matter added to the soil must be large enough to change the soil structure. Spread from 1 to 4 inches over the soil and then till or mix it in. As organic matter decomposes into humus, it continues to improve the soil. For best results, add organic matter whenever the soil is worked. Many different types of organic matter can be used as soil amendments. The amendments should be free of weed seeds, toxic materials, and disease organisms. When buying organic matter, especially in bulk, it is best to buy from a well-established, reputable dealer. The most commonly used types of organic matter are compost, peat moss, manure, ground bark, and sawdust, but other materials may be available locally.

Compost: Compost can be purchased or made at home. It improves soil structure and, depending on what originally went into it, provides some of the essential nutrients for plant growth.

Peat moss: Peat moss is one of the most commonly used soil conditioners. Since peat moss is acid (pH 3.5 to 4.5), it is especially good for acid-loving plants; enough peat moss may be added before planting to make up 50 percent of the amended soil. If peat moss is allowed to dry out, it will shed water. It can be remoistened by loosening the peat moss, spreading it under a sprinkler, and then mixing it several times while it is absorbing water. If the peat moss is already mixed into the soil and it does not moisten, add a wetting agent, which can be purchased from your local nursery, to the water.

Manure: Manure is a very common and widely available soil amendment. It is a good conditioner, but has several drawbacks. Fresh manure may burn tender roots, so it should be partially decomposed before it is used. Some manure, especially bagged steer manure, has a high salt content, and should be used in moderation if you already have a salt problem or alkaline soil. (For more information about salt damage, see Salt Damage.)

Ground bark and sawdust: Ground bark and sawdust are by-products of the lumber industry. Unless they have been fortified with nitrogen (if they are purchased in bags it will say so on the bag) or are well composted, the bacteria that decompose them will rob the soil of nitrogen. To prevent a nitrogen deficiency, add ½ pound of nitrogen to every cubic yard of bark or sawdust.