Compost may be the home gardener’s best friend. Used as organic mulch, compost helps water retention and soil cooling. As a soil amendment, compost adds organic matter and improves soil structure and drainage. Compost can also be used to make a kind of liquid fertilizer that adds nutrients to plants. Here’s a look at the three main uses for compost in your home garden – mulch, soil additive, and as a fertilizer or “compost tea.”
Mulch may be the best-kept secret of compost. Mulch helps water penetrate the soil by lessening erosion and water runoff during rainfall. A layer of mulch helps water to be more easily absorbed into the soil. Mulch can also help keep soil cool during hotter months. And, of course, mulch helps smother out weeds.
Compost that is lower in nitrogen, sometimes called brown compost, is especially suitable for use in the garden as mulch. Avoid using compost from a composter or compost pile that is not yet finished decomposing; this can actually rob the soil of nutrients. Keep the mulch layer at one-inch to two-inches to avoid creating space for insects and other pests. Follow garden guide recommendations for allowing space between tree trunks and shrubs and the ring of mulch, because mulch applied too thickly or too closely may actually harm plant health.
Compost is at its best as a soil amendment, incorporated into the garden soil, adding organic matter and bettering soil structure. Finished compost may even be used as a medium for starting seeds. Before digging beds or planting the spring garden, spread an inch or two of compost on top of the soil. Work that into the soil, digging to a depth of about six inches. This can improve the soil’s condition, which results in better plant root growth and development.
Compost is not technically a fertilizer, but adding more organic matter to the soil with compost promotes the gradual release of nutrients to plants. You can compound the benefits of compost in your garden by both working it into the soil before planting and using compost to mulch around plants during growth.
Compost can also be used to make compost tea, which may contain some nutrients beneficial to plants. Older garden guides promoted “brewing” compost teas by letting compost sit in a bucketful of water, then applying water to plants. Nutrients diluted out of the compost into the water. While this is still a way of delivering nutrients to plants using compost, many compost teas today are made using active aeration (bubbling), which helps increase aerobic microbes in the tea. The microbes in compost teas may be beneficial for guarding plants against disease, adding to the boost your plants will get from properly made and applied compost tea.