Released: June 19, 2001

Mulching Pays, But Only If Used Correctly

MANHATTAN, Kan. – Mulch pays for itself in summer by helping conserve soil moisture, keeping plants’ root zone cooler, and reducing both weed growth and soil compaction. It also keeps garden plants cleaner – everything from flowers in a patio pot to vegetables on a sprawling vine.

Even so, mulch can cause problems, too, if not used correctly, said Kansas State University horticulturist Chuck Marr.

"Landscape fabric or perforated black plastic mulch usually works best with many of the permanent landscape plants and with large-leaf, warm-season vegetable transplants, including melons, peppers and eggplant," he said. "If nothing else, it can help prevent rotting by keeping tomatoes and squashes away from soil contact.

"But, fabric and plastic also can inhibit perennial plants’ expansion. They can warm up the soil too early in spring, putting tender plants at risk in case of a late frost. Plus the plastics, in particular, can promote root rot in such plants as junipers and arborvitae by holding in moisture too long during wet periods."

Organic mulches (compost, old hay, shredded newspapers, sawdust, straw, leaves, cotton hulls, peat moss, wood chips, grass clippings and the like) bring a bonus. Over time, they improve soil as they decay, when they are tilled in at the end of each growing season.

"Dried or composted materials are best. Fresh organic materials can generate heat, form molds or slime, smell bad, and repel water," said Marr, who is K-State Research and Extension’s vegetable crops specialist. "Naturally, you’ll also want to make sure organics don’t contain weed seeds, insects or disease organisms that could spread."

To function as they should, however – neither serving as mere decoration nor killing plants – organic mulch applications must match layer depth to individual piece size:

* Large, coarse materials (straw, wood bark) – the larger, the deeper. But, no less than 3 inches and no more than a 4- to 5-inch layer.

* Small and/or fine materials (peat moss, grass clippings) – the smaller, the more shallow. But, no less than 1 inch and no more than a 2-inch layer.

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K-State Research and Extension is a short name for the Kansas State University Agricultural Experiment Station and Cooperative Extension Service, a program designed to generate and distribute useful knowledge for the well-being of Kansans. Supported by county, state, federal and private funds, the program has county Extension offices, experiment fields, area Extension offices and regional research centers statewide. Its headquarters is on the K-State campus, Manhattan.

Story by:
Kathleen Ward, Communications Specialist
kward@oznet.ksu.edu
K-State Research& Extension News