How to Topdress Plants With Compost. Most gardeners incorporate compost into their garden's soil, but compost can also be used as a topdressing (or mulch). Placing compost directly on the soil has several advantages. It helps keep down weeds and holds moisture in the soil, and the compost also slowly releases nutrients to your plants. Plus, it makes the garden look neat and tidy. Here's how to topdress.
Before applying any kind of mulch, compost or otherwise, it is important to thoroughly weed the garden and water the soil in well. Aim to soak the soil to a depth of about 8 inches.
Compost that is completely finished-meaning you won't be able to identify any of the original ingredients and it does not contain any sticks or other woody material-works best for topdressing. Commerical compost that you can buy in bulk or in bags is typically completely finished. Homemade compost, however, tends to have woody material that is not fully decomposed. If this is the case with your compost you can either screen out the woody material or just purchase a few bags of compost for the purpose of topdressing.
Spread a 1- to 2-inch layer of finished compost between your plants. Prevent smothering your plants by leaving a little donut-shaped well around the base of each plant, then water the compost in well.