Compost, the dark, crumbly result of decomposed organic matter, serves as a fundamental amendment for improving garden soil. It acts as a mild, slow-release fertilizer and significantly enhances soil structure, aeration, and water retention capacity. Understanding the methods and timing for application is key to maximizing these benefits. This guide focuses on the practical steps involved in readying and applying compost for surface maintenance or deep soil building.
When and How to Prepare Compost for Use
The optimal timing for compost application is either in early spring, just before planting, or in the fall, after the main growing season has finished. Fall application allows the organic matter to break down and integrate with the soil throughout the winter months, offering a nutrient-rich foundation for the following spring. Applying compost in the spring provides an immediate boost as plants begin their active growth phase, ideally two weeks before putting seeds or seedlings into the ground.
Before spreading, ensure the compost is fully cured, appearing dark and crumbly with a pleasant, earthy scent. Immature compost may contain active microbes that temporarily draw nitrogen from the soil, potentially harming young plants. Screen or sift the material to remove larger, undecomposed pieces. Using a simple sifter made with half-inch hardware cloth allows the finer material to pass through, ensuring easier, more even application.
Surface Application Techniques
Surface application, often referred to as top dressing, is a maintenance technique for established garden areas that avoids disturbing the soil structure. This method involves spreading a thin, even layer of finished compost directly onto the soil surface, allowing soil organisms and water to naturally pull the nutrients down over time. For vegetable and flower beds, a layer of about one-quarter to one-half inch is typically sufficient for an annual maintenance application.
Top dressing also provides a protective layer that helps moderate soil temperature and reduce water evaporation. When applying around established perennial plants, trees, or shrubs, spread the compost in a ring, avoiding direct contact with the base of the plant or trunk. This prevents moisture from collecting against the stem, which could encourage rot and pest issues.
A specific type of surface application is side dressing, which is used to give actively growing plants a mid-season nutrient boost. This involves placing a handful or a thin strip of compost a few inches away from the base of heavy feeders like tomatoes or squash. The compost should be placed near the plant’s drip line, where the active feeder roots are located.
For turf grass, top dressing with compost improves soil health and reduces thatch, but requires a thin layer to avoid smothering the blades. Spread a finely screened layer no more than one-quarter to one-half inch thick across the lawn surface, using a spreader or a shovel for even distribution. After any surface application, a light watering helps the fine particles settle down to the soil level and begin nutrient release.
Incorporating Compost into Soil
Deep incorporation is the method used when building new garden beds, filling raised beds, or preparing existing soil that needs structural improvement. This process involves physically mixing a substantial volume of compost into the native soil to create a fertile foundation. For new garden beds, spread a layer of three to four inches of compost across the soil surface.
The compost is then mixed into the top six to twelve inches of the existing soil using a garden fork, spade, or tiller. This blending action immediately improves the soil’s tilth, increasing pore space for better drainage and root growth while distributing the organic matter evenly. A good starting ratio for a new garden area is to aim for roughly one part compost blended with two to three parts native soil.
When filling new raised beds or containers, compost is a necessary component but should not be used exclusively. It is best combined with other materials like topsoil and a drainage agent to create a balanced, durable growing medium. Common mixes include a 50/50 blend of screened topsoil and compost, or a three-part mix that includes a soilless component like peat moss or coir. This deep incorporation is generally completed weeks before planting to allow the soil mix to settle properly.