We hear again and again that adding organic matter to soil will solve all garden and landscaping issues: just dig a hole, add your tree, throw in some compost, and voila—improved soil and a healthy tree! But soil expert Dr. Carl Whitcomb (Whitcomb, 1987) disagrees. His research finds that adding organic matter, such as compost, to individual plantings is not the best approach. How did he find out? Dr. Whitcomb wanted to know, when people are putting in new plantings, how much organic matter should be added to the native soil. His answer: none. It sounds strange, but the professor found that individual plantings do best in native soil alone—with no amendments. This may be because mixing different sizes of soil sucks moisture from the roots or because the tree likes the rich, amended soil so much that its roots don’t spread into the native soil.
Dr. Whitcomb recommends that people who add plantings to their landscape should use only native soil and should not amend their soil with any organic matter at all. He does say, however, you should add mulch on top of the soil. Mulches such as pine straw and nuggets will break down and add organic matter to the soil from the top down, which mimics natural processes.
But don’t give up on compost yet. Your garden still loves it. Dr. Whitcomb’s native-soil-only approach applies to single holes dug for single plants. We recommend that beds for large numbers of plantings still benefit from addition of compost and other organic materials. When preparing your large bed for lots of plantings, add organic matter and till it into the native soil. This will give your plants lots of loose soil for healthy root growth.
Whitcomb, C. (1987). Establishment and maintenance of landscape plants. Lacebark, Inc.
Compost your way to a luxury landscape.