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You are here: Home ›› Learn ›› Resources ›› Compost ›› What is Mulch?

What is Mulch?

Get an overview of mulch, what it is and why to use it, some history, and more resources for further research.

Mulch is any material placed around plants usually a few inches deep to reduce weeds, increase or decrease soil temperature, retain soil moisture and reduce soil compaction. The type of mulch one uses will depend on the function and the aesthetic value of the landscape.

Organic mulches such as compost, bark, wood chips, leaves, seed hulls, grass clippings, nut shells, newspaper, cardboard, or straw have the added benefit that they add nutrients to the soil as they decompose. This type of mulch needs to be periodically reapplied.

Inorganic mulches such as gravel, black plastic, or fabric perform many of the same functions as organic mulch but do not add organic matter to the soil.

There are also living mulches such as clover and ground covers that can be used to overwinter garden beds or when other types of mulch are not desired.

Mulches should be applied evenly around trees, shrubs, and perennials, but never deeper than four inches.  Mulch should be kept about an inch away from the main stem or stems of a plant and should never be piled against the trunk or over the top of a plant. For plants or trees in the lawn, a three to six foot ring should be applied extending out from the trunk, whereas for plants in beds it is best to mulch the entire bed.

Mulches can be applied in spring or fall depending on the desired effect.  In spring, mulch will help prevent weed seeds from sprouting, add nutrients to the soil (if organic) and keep soil temperatures cooler over the summer.  Mulch applied in the fall will help keep soil temperatures warmer through the coming winter.


The English word mulch is probably derived from the German word molsch, meaning soft, beginning to decay. It no doubt referred to early gardeners' use of straw, leaves, and loose earth spread on the ground to protect the roots of newly planted trees and shrubs.


Virgina Tech Cooperative Extension

SERG: Soil Ecology and Restoration Group at San Diego State University

Call The Garden Hotline for individualized help: 206-633-0224


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