Mulch in the Xeriscape

Mulch not only discourages weeds, reduces erosion, and dresses up the garden, in the desert landscape, it also serves the vital purpose of cooling the soil and conserving water. Adding mulch to your landscape can do more for your plants than most soil amendments can.

Which mulch is right your xeriscape?

There is a wide variety of both organic and inorganic mulch out there, but they're not all interchangable. Mulch should be chosen to suit the plants, local climate, and soil. For instance, in desert climates, most crops will grow better with a soil-cooling mulch such as shredded leaves, wheat straw, or newspaper. This is especially true for cool-weather crops such as broccoli and lettuce. These types of mulch can lower soil temperatures by as much as 20 degrees Fahrenheit (10 degrees Celsius), which may keep plants going right through summer. If you use this type of mulch in early spring, though, make sure the soil has had time to warm up and dry out first.

Plastic mulch is generally not a good idea in high temperatures on dry, sandy soil. Plastic mulch can become too hot and damage your plants. What's more, plastic mulch doesn't allow water through, so it could cause plants to dry out.

Visit D-L's types of mulch page for more information on which much to use in your xeriscape.

When and how to apply mulch

Mulch is best applied at the end of winter or the start of spring while the ground is still damp from winter rains, but before the hot weather starts. Avoid piling mulch on top of perennials or bulb plants before they emerge in spring as this can cause the plants to rot. Before applying an organic mulch, especially leaves and straw, consider adding nitrogen-rich fertilizer. One problem with organic mulch is that as it decomposes, it draws nitrogen from the soil and a fertilizer can help balance this effect. When you lay the mulch, first place a few layers of newspaper on the ground to improve water conservation.

Many types of organic mulch material should be allowed to sit before being applied to the landscape. While you should never use clippings from lawns treated with herbicides or toxic pest controls, even otherwise clean lawn clippings should be left to dry in the sun for a few days before being used. If you use leaves, let them age for at least nine months to be sure they no longer contain phenols, which can impair growth in garden plants.

To do its job, mulch must be applied at the appropriate thickness. Keep mulch around soft-stemmed annuals and perennials at about 2 or 3 inches (5-7 cm). Less than this and weeds will grow right through. Any deeper than 4 inches (10 cm), though, and the mulch could reduce air circulation in the soil. When you apply the mulch, keep it at least an inch away from plant stems to prevent bark rot and fungus problems.