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Horticulturist digs up some garden truths

Thu., Oct. 8, 2009

Fall is the most important time to fertilize a lawn. Special to  (Pat Munts Special to / The Spokesman-Review)
Fall is the most important time to fertilize a lawn. Special to (Pat Munts Special to / The Spokesman-Review)

We’ve all received the e-mail or junk mail piece promoting the product, process or plant will solve all our garden problems quickly and cheaply. Is it a myth or is it good garden science?

In general, myths are often corruptions of sound garden science that play on our need for a simple explanation and reassurance that we are good gardeners if we follow them. Scott Aker hears a lot of them as a horticulturist with the U.S. National Arboretum in Washington, D.C. He shared some of the more common ones along with the real story at a recent garden writers’ conference.

Myth: To loosen clay soil, add sand to the soil.

Truth: Sand added to clay soil causes the flat clay particles to clump together forming an even denser soil. To loosen clay soil, add organic material or gypsum and mix it in well.

Myth: Deep injection fertilization of trees and shrubs promotes growth.

Truth: Contrary to the idealized concept of a tree sending its roots deep into the soil, most tree and shrub roots spread out in the top 18 to 24 inches of the soil. Injecting fertilizer down two or more feet in the ground actually puts it beyond the reach of the tree’s root system where it is wasted. Most trees and shrubs do fine in native soil without fertilization of any kind. If you want to help your trees, make sure they get enough water by deep soaking them down at least two feet every couple of weeks. To check this, water a tree and then dig down to see how far the water actually went.

Myth: Mycorrhiza added to garden soils promotes plant growth.

Truth: This is a half myth. Mycorrhiza fungi don’t need to be added to garden soil because they already occur there. They colonize roots creating a symbiotic relationship that benefits both the plant roots and the fungi in the process. In the case of sterile potting soils however, adding mycorrhiza can benefit potted plants by restoring natural fungi to the growing process.

Myth: Breaking up the root balls on container grown plants will harm the plant

Truth: Roughing up root balls frees the roots to move into the soil. Container bound plant roots will continue to grow in a circular shape unless they are freed. Tease roots free by rubbing the root ball and/or cutting some of the circling roots so the root ends stick out and then plant.

Myth: Fescue and bluegrass lawns need to be fertilized in the spring but not in the fall.

Truth: The most important time to fertilize a lawn is in the fall when the plants are storing reserves for next year. The grass then has the reserves to begin growing quickly in early spring which helps crowd out early weeds reducing the need for herbicides. Use an organic fertilizer that provides nitrogen in a form the grass can easily take up. Make plans to mulch mow next year to further reduce the need for fertilizer.

Pat Munts is a Master Gardener who has gardened the same acre in Spokane Valley for 30 years. She can be reached by e-mail at


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