In the Garden:
Southwestern Deserts
October, 2012
Regional Report

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In addition to inhibiting weeds, moderating soil temperature, and and maintaining soil moisture, decomposed granite mulch provides an attractive background for plants.

Xeriscape Part V & VI: Soil Improvement & Mulching

Xeriscape design includes a set of seven principles to guide you in the creation and long-term maintenance of a colorful, earth-friendly landscape that suits your unique needs. Previous reports covered design and site analysis, whether to install turf, varied plant selection subjects, and effective watering techniques.

Soil Improvement
Enjoy this money- and labor-saving tip regarding soil improvements: if you are growing native or desert-adapted low-water-use plants, soil amendments in the planting hole are seldom needed. Changing the soil profile around root systems with amendments may actually do these plants a disservice. Roots tend to grow round and round in their richly amended "cocoon," rather than pushing themselves beyond the "barrier" when they reach native soil. Evidently, roots feel they've hit a brick wall and need go no further. This is problematic because roots need to stretch out far beyond the plant canopy edge to develop a strong anchor, as well as seek water and nutrients.

However, if you decide to add turf to your xeriscape, you will need to amend the soil before installation. Also, because there are varied soil profiles across the Southwest, you may live in a pocket where amendments are beneficial for non-native landscape plants. On the other hand, soil amendments break down and leach away within a year or two, and the non-native is ultimately surrounded by native soil that may not be prime for its long-term growth. (Another reason to stick with native or well-adapted desert plants during your selection process.) If you have concerns regarding your specific soil, check with your local County Cooperative Extension office for recommendations specific to your area.

A layer of mulch covering soil is an essential component of any xeriscape. Either organic mulches (bark chips, wood shavings, compost, lawn clippings, pine needles, and leaves) or inorganic mulches (decomposed granite and crushed rock) reduce water evaporation from the soil, insulate against hot and cold temperature extremes, inhibit weeds from sprouting, and reduce erosion. Organic mulches also add nutrients to the soil as they break down.

Cover all bare soil with 2 to 4 inches of mulch but leave several inches of bare soil around plant stems and trunks. Mulch rubbing against plant tissue creates conditions conducive to diseases and pests. Replenish mulch yearly or as needed.

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