If you are a regular reader, then you know that Master Gardeners are always promoting the mulching of garden beds. The benefits of a three to four inch layer of mulch around plants helps moderate the soil temperature, conserve water, reduce or eliminate weeds, and help with erosion control. An organic mulch also enriches the soil while providing the garden with a neat and cared for look.
However, as more gardeners are adding native plants to their gardens, (the recent native plant sale is a testament to that!) it is important to use the right mulch for these plants. In the April-June 2009 edition of the California Native Plant Society’s Bulletin, Barbara Eisenstein, the horticulture outreach coordinator at the Rancho Santa Ana Botanic Garden, writes that when selecting mulch for native plant gardens, it is important to know what mulch is appropriate for native plants. She states that gardeners should learn where the plant grows naturally and what type of soil covering is around the plant in order to provide the right mulch.
“Woodland soils are usually covered by a deep layer of organic material. Chaparral and scrubland have little organics on the soil, though some do collect along with pebbles and inorganic debris.” She goes on to state, that “using organic mulch in gardens that feature desert, chaparral, or scrub plants can produce undesirable results. If the mulch remains too moist, these plants are more likely to rot. Furthermore, in time organic mulch enriches the soil. Dry plants are adapted to lean soil. In enriched soil they may respond with lush growth that dehydrates during hot weather, resulting in extreme stress or even death. On the other hand, plants adapted to wetter more verdant regions appreciate a layer of organic material. Inorganic mulch can get too hot in summer, too cold in winter and does not hold water nearly as well as organic mulch.”
Since my garden is now comprised of over 80% native plants, I am planning to revamp my mulching techniques. The salvias, penstemons, ceanothus and buckwheats will now be mulched with pea gravel or decomposed granite. These plants all enjoy a drier type landscape. However, many of the native shrubs and ferns will continue to be mulched with organic material as most grow under canopies of trees that provide a deep layer of organic material.
If you are uncertain where your native plants naturally grow and what type of mulch you should use, call the Master Gardener Hotline at 209-533-5912. You can also stop by the Demonstration Garden on Open Garden Day (the first Saturday of each month) from 10:00 am to 1:00 pm. Consider attending the monthly meeting of the Sierra Foothill Chapter of CNPS on the first Thursday of each month in the meeting room at the Tuolumne County Main Library on Greenley Road.
Just remember that whatever type of mulch you use, keep it at least 2 inches away from the trunks or stems of plants. If you use a thick layer (4-6 inches) of organic mulch, be sure and water enough to soak the soil beneath the mulch and then give the soil a chance to dry out before watering again.
And in case you were wondering about rubber mulch, consider this. Linda Chalker-Scott of Washington State University concludes in her review of scientific studies that this is an inappropriate material for mulching for the following reasons: it is not as effective in controlling weeds, it is highly flammable and difficult to extinguish once it begins burning, and it contains a number of metal and organic contaminates with known environmental and/or human health effects.
You have heard the saying, “Right plant, right place.” Now with this new mulching information for natives we might say, “Right plant, right place, right mulch!”
Carolee James is at this moment removing organic mulch and spreading pea gravel and decomposed granite around some of her natives.