Mulch Problems: Solved

By Melinda Myers, Horticulture Expert

What is the yellowish-beige stuff on my wood chip mulch? It looks like my neighbor's dog got sick in my garden.

Melinda: This slime mold, often called "dog vomit fungus," is common on wood chip, cocoa bean and a few other organic mulches during wet weather.

The fungus feeds on organic matter in the mulch. It looks disgusting, but it won't hurt your plants, and will disappear when the weather dries. to prevent it, lightly rake mulched areas during wet weather.

My flowers are pale and stunted. Is the wood chip mulch stealing nitrogen from them?

Melinda: Wood chips, sawdust and other wood mulches break down slowly. The microorganisms helping them decompose use soil nitrogen as an energy source. this ties up nitrogen the plants would like to use and can lead to yellowing and stunted growth. Once the chips decompose, that nitrogen and more is available to the plants.

This isn't a problem for most large-root plants like trees and shrubs. For smaller plants, I recommend adding a little supplemental nitrogen to compensate. Avoid tilling wood mulches into the soil at the end of the season, too, or limit their use to paths and areas around trees and shrubs.

Is it safe to shred tree leaves and use them as mulch in the garden or on the lawn?

Melinda: Autumn leaves like oak or maple make great mulch in the garden. When shredded with the mower, they can be left on the lawn.

Don't allow large leaves to remain intact on the lawn, though—they block light and trap moisture, which can be detrimental to your grass. Shredding speeds up decomposition and gets nutrients into the soil faster. As long as you can see the grass through the shredded leaves, your lawn will be just fine.

You also can add shredded leaves to your compost pile or work them into vacant gardens in the fall.