Gardening Articles: Landscaping :: Lawns, Ground Cover, & Wildflowers

Gardening Fact...or Fallacy? (page 2 of 2)

by Robert Kourik

3. When planting trees and shrubs, the more compost, peat moss and other amendments you can mix into the ground, the better.

In the early 1970s, Carl Whitcomb, a researcher at Oklahoma State University, disproved this oft-repeated advice. In controlled studies using percentages of different amendments (up to 40%), roots of ornamental trees and shrubs were consistently larger in unamended soils. The amendments seemed to encourage roots to stay in the vicinity of their planting holes and not grow out into the unamended soil, leading to stunted root systems. Whitcomb concluded that it's best to let the roots begin to grow in the nativ soil right away and to use organic matter on the surface as a mulch, rather than mixing it with the soil. If a tree isn't suited to native soil, you are better off growing it in a container than trying to change the soil with amendments.

4. When pruning, always cut tree branches flush to the trunk.

Though U.S. Forest Service worker Alex Shigo debunked this myth some 20 years ago, the news is just now getting around. A truly flush cut does serious damage to a tree. You should leave the branch "collar," a swelling or shoulder around the base of each limb. Shigo discovered that this collar has the ability to produce chemical changes in the area behind a break or cut that preserve tissue and confine decay to a small area, preventing it from moving into the core of the wood. Look at trees in your walks around town or in the woods, and you'll begin to notice these collars, which differ in size and shape with each species.

5. When planting a bare-root tree, prune away enough branches to balance the top with roots lost when the tree was dug.

When a bare-root tree begins to grow, it's able to limit new shoot and leaf growth to the capacity of the root system on its own. Pruning takes away some of the healthiest buds and robs the tree of stored energy. More ground-breaking work by Carl Whitcomb in 1979 demonstrated that removing apical buds provided little benefit to ornamental trees. He showed that trees pruned by more than 15% exhibited "reduced visual quality" as they matured.

If, however, a new tree has a broken limb, prune it back to the nearest strong bud or side shoot. After the tree has grown for a season and recovered from the stress of transplanting, begin pruning for a balanced shape with well-positioned main limbs. Use the least number of cuts possible.

6. Put a layer of gravel in the bottoms of pots to provide drainage.

A little common sense disproves this chestnut as well. If the soil in the bottom of a pot stays wet, a plant's roots get waterlogged and rot. But it's the holes in the bottoms of containers that allow the water to flow through. In pots with no drainage holes, a layer of gravel will do no good. In fact, any gravel in the bottom reduces the volume available for potting soil, as well as making everything heavier than it needs to be. All that's needed is a small fragment of terra-cotta over the pot's drainage holes to keep the soil from slipping out. If the pot rests in a shallow saucer, don't habitually keep the saucer full of water or roots in the bottom layer of soil will be damaged.

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