Finished compost is dark brown, crumbly, and is earthy-smelling. Small pieces of leaves or other ingredients may be visible. If the compost contains many materials which are not broken down, it is only partly decomposed. This product can be used as a mulch, but adding partly decomposed compost to the soil can reduce the amount of nitrogen available to the plants. The microorganisms will continue to do the work of decomposing, but will use soil nitrogen for their own growth, restricting the nitrogen’s availability to plants growing nearby.
Allow partly decomposed compost particles to break down further or separate them out before using compost on growing plants. Or add extra nitrogen such as manure, to ensure that growing plants will not suffer from a nitrogen deficiency.
Compost serves primarily as a soil conditioner, whether it’s spread in a layer on the soil surface or is dug in. A garden soil regularly amended with compost is better able to hold air and water, drains more efficiently, and contains a nutrient reserve that plants can draw on. The amended soil also tends to produce plants with fewer insect and disease problems. The compost encourages a larger population of beneficial soil microorganisms, which control harmful microorganisms. It also fosters healthy plant growth, and healthy plants are better able to resist pests.
One inch thick is enough to spread on your garden beds. Compost continues to decompose, so eventually the percentage of organic matter in the soil begins to decline. In northern climates, compost is mostly decomposed after two years in the soil. In southern climates, it disappears even faster and should be replenished every year.
To bolster poor soil with little organic matter, spread 2 to 3 inches of compost over a newly dug surface. Then work the compost into the top 6 inches of earth.
A garden soil that has been well mulched and amended periodically requires only about a ½ inch layer of compost yearly to maintain its quality.
Some people recommend late fall as a good time to spread compost over a garden bed, and cover it with a winter mulch, such as chopped leaves. By spring, soil organisms will have worked the compost into the soil. Others recommend spreading compost two weeks before planting time in the spring. There is really no wrong time to spread it. The benefits remain the same.
If your supply of compost is really limited, consider side-dressing, a way to use compost sparingly by strategically placing it around certain plants or along certain rows. This is best done in late spring and early summer so that the rapidly growing plants can derive the maximum benefit from the compost.
To side-dress a plant, work the compost into the soil around the plant, starting about an inch from the stem, out to the drip line, taking care not to disturb the roots. For shallow rooted plants, leave the compost on the soil surface. A 2″ layer works best when left on top.
For new lawns, a 2 to 3″ layer of compost is best when planting. Once the new lawn is established, a ¼ to ½” layer yearly will maintain the quality of the soil.
An existing lawn top-dressed with a ½” layer of compost every year or two will be healthier than an unamended lawn. Fall is the best time to apply the compost, although an application in early spring is almost as effective.
A compost mulch can benefit trees and shrubs just as it does other plants. Spread a ½” to 1″ layer of compost on the bare soil under the tree as far as the drip line. Then cover with a 2-3″ layer of some other kind of organic mulch, such as chopped leaves or pine needles. The mulch will hold the compost in place and keep it from drying out.
Adding compost to the planting hole of small perennial plants is valuable, particularly perennial food plants. Annuals will also benefit from a dose of compost at planting time.
Compost is the ultimate garden fertilizer. It contains virtually all the nutrients a living plant needs and delivers them in a slow-release manner over a period of years. Compost made with a wide variety of ingredients will provide an even more nutritious meal to your growing plants.
Compost is the best material available to enliven your soil no matter where you live. Farmers around the world will testify that healthier soil grows healthier plants that naturally resist disease, insects, and other environmental pressures. Adding compost to your garden is a long-term investment – it becomes a permanent part of the soil structure, helping to feed future plantings in years to come.