Mulch helps trees and shrubs survive dry periods

By Gary Johnson, University of Minnesota Extension

ST. PAUL, Minn. (8/6/2007) — For trees and shrubs, the single, most effective way to moderate soil moisture fluctuations and reduce irrigation is to apply a generous layer of mulch (preferably organic).

It is astonishing how long the soil below a generous mulch layer remains moist, even in droughty periods. In addition to moderating soil moisture extremes, organic mulches break down and continuously add organic matter to the soil horizon.

Use a minimum of three to four inches of coarse organic mulches (e.g., wood chips, but not redwood nuggets), or two to four inches of finer mulches (shredded bark, hulls, composted leaves). Don’t pile the mulch against the stems of plants.

If you annually add a fresh topping of mulch, do not remove the old mulch. When old mulch is removed, all of the wonderful fine roots of the trees and shrubs are removed, too. Treat your trees and shrubs as a forest or prairie does with annual, light applications of organic materials. (Natural areas do this with their old leaves, dead roots, dead branches and thatch.).

Mulches don’t make water--they conserve water. Make certain that the rhizosphere (root environment) is thoroughly moistened before the mulch is applied. Use a soil probe to check.

If there is turf around the plants, place five to 10 layers of newspapers over the turf, soak the newspapers and then apply the mulch. If you don’t have old newspapers, kill the grass with glyphosate, carefully avoiding any spray drift to young stems, leaves and your neighbor’s vegetable garden.

If mineral mulches (gravel, crushed rock, etc.) are more desirable, then use a weed fabric groundcover before the mineral mulch is applied. Try to avoid using plastic as a groundcover. Generally, organic mulches are preferred for plant health.

Any use of this article must include the byline or following credit line:
Gary Johnson is an urban forestry specialist with University of Minnesota Extension.

Media Contact: Julie Christensen, U of M Extension, (612) 626-4077, reuve007@umn.edu

URL: http:// www.extension.umn.edu/extensionnews/2005/2007mulch.html  This page was updated Aug. 21, 2007 .
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