The best (and easiest) way to improve the soil in your garden is to top-dress with compost. Top-dressing involves spreading a 3 to 5 centimetre (or 1 to 2 inch) layer of compost on top of the soil. You can make your own compost or buy good quality compost from your local nursery or landscaping company.
Top-dressing garden beds: If the soil is covered with a layer of mulch, gently move it aside. Apply a ring of compost around each plant, then replace the mulch. Be sure that the compost and mulch do not touch the stems of your plants. Some plants, like native prairie plants, prefer low-nutrient soil, so adding compost to prairie plantings is not advised.
Top-dressing around trees and shrubs: For newly planted trees and shrubs, spread a mixture of compost and mulch on the ground above the root ball and 20 to 30 centimetres (8 to 12 inches) beyond the planting hole to encourage healthy root growth. You can purchase compost-mulch mixes or make your own by mixing one-part compost to four-parts wood chip mulch. After applying, pull the compost and mulch away from the trunk to create a doughnut shape.
Even mature trees and shrubs benefit from a layer of compost on the ground below their branches in the spring and early fall.
When top-dressing, you do not need to dig it in. Worms and other soil organisms will gradually move the compost into the soil. This method feeds your soil and plants while protecting the soil from disturbance.