Compost consists of decomposed plant and organic matter. It adds nutrients to the soil as well as aiding overall soil quality. Compost improves drainage and aerates clay soils, while adding much-needed organic matter to sandy soils. Make your own compost from fallen leaves and grass clippings or purchase compost from garden centers. Purchased composts may be made completely of plant material or may contain some composted animal manures as well. Apply compost to a garden before you plant annuals in the spring, and around existing perennial plants.
Place a 4-inch layer of compost over annual flower beds or new flower beds in spring just prior to planting. Till the compost into the top 6 to 8 inches of the soil with a spade or power tiller. Use up to an 8-inch compost layer if you are improving heavy clay soils, as the compost helps break up the clay.
Spread a 2-inch layer of compost over the bed and around perennial plants and shrubs. Compost acts as a mulch, preserving soil moisture and preventing weeds, as well as leaching nutrients into the soil over time. Replace the compost mulch each year.
Spread a 2- to 4-inch layer of compost around trees in the spring. Spread the compost out to the drip line of the tree, which is the outer edges of the branch canopy. Leave a 2-inch space between the trunk and the compost, or pests may burrow into the compost and attack the trunk.
Mix 1 part compost with 1 part peat moss and 1 part sand or vermiculite and use this as a potting soil for both houseplants and outdoor container gardens. The compost adds nutrients to the potting mixture and provides drainage. Additional fertilization may need to be added to a compost mix, depending on the specific requirements of the plant.
Place a 1-inch layer of compost on top the soil in existing plant pots when the plants begin actively growing in spring. Adding compost improves the quality of the soil in the pot, as each watering leaches the nutrients of the compost into the existing soil.