Use of Straw as Mulch: A Cover Story

November 13, 2004

By Suzzanna Walsh, Master Gardener

Thinking of using straw as mulch brings to mind the old Tamil Indian proverb: “Even old straw may be of use sometime or other”.

First, a quick review; Major reasons to mulch your garden are:

1) Conserve moisture. Remember we are in a coastal dessert and water conservation is very important.

2) Smother weed growth. I don’t know about you, but I would rather spend more time enjoying the flowers and vegetables in my garden than pulling weeds.

3) Moderate soil temperature. You probably want to avoid extreme fluctuations in your soil's temperature, maintaining it so that it is neither too hot nor too cold but ‘just right’. A special note to those of you in the North County: a thick application of mulch will slow the spring warming of the soil, so you might want to wait to apply thick mulch for your annuals and vegetables until the soil has warmed a bit.

4) Prevent soil erosion.

When determining the type of mulch you want to use in your garden consider straw mulch for the following reasons:

1) Because it is organic mulch it adds beneficial nutrients to your soil and improves structure, remembering, of course, that mulch is not a soil amendment.

2) It’s readily available at most farm supply centers. The average cost of a bale of straw is $6.75.

3) Straw’s rate of decomposition is slower than some other types of mulch.

Straw as mulch can tie up nitrogen at the soil surface during decomposition so it is best used around fruit trees and not around annual plants. Oat straw should be avoided if you desire weed control as part of your mulching requirements. To make sure your straw is weed free, try the following:

1) Buy straw that is already rotting.

2) Leave your straw bales out over the winter so that the combination of wet and dry weather can cause the straw to start the rotting process, killing weed seeds at the same time.

To lay your straw mulch just pull apart the sections of your straw bale and lay it at least three to four inches thick, remembering to use gloves to protect your hands. Do not let the straw become matted down. To get the best out of straw mulch it is necessary to keep it fluffy instead of tightly compacted - easy enough!

One added benefit - to be both environmentally friendly and frugal, buy your straw bales now and use them as part of your harvest decorations. Let them finish rotting and add to your garden in the spring.

University of California Cooperative Extension Master Gardener Volunteers can provide additional gardening information upon request. Call the San Luis Obispo office at 781-5939 on Mondays and Thursdays from 1 to 5 PM, the Arroyo Grande office at 473-7190 on Wednesdays from 9 AM to 1 PM, or the Paso Robles office at 237-3100 on Wednesdays from 9 AM to Noon.  The San Luis Obispo Master Gardener website is at http://groups.ucanr.org/slomg/. Questions can be e-mailed to mgsanluisobispo@ucdavis.edu.