   Slowing Erosion with Native Grasses - January 28, 2004 Jeff Schalau, County Director, Agent, Agriculture & Natural Resources Arizona Cooperative Extension, Yavapai County Erosion is a natural process, but disturbances can accelerate the rate of soil loss. To retard this effect, the soil surface must be protected by some form of cover. Erosion usually begins with raindrop impact. The energy released by the raindrop causes soil particle to go into suspension and move with the water. As flowing water accumulates, it forms rills and gullies that further accelerate erosion. Once flowing water slows, the energy dissipates and soil is left behind as sediment. This is called deposition. In landscapes, we usually want to retard erosion. However, bare areas are inevitably left behind following construction or other major disturbances. In many cases, erosion can be mitigated by using mulches. Rock, gravel, chips, and bark dissipate the energy of raindrop impact and allow the water infiltrate the soil surface and percolate through the soil. Soils have a limited capacity for absorbing water and during intense rainfall events we can expect some overland flow. Anytime unoccupied growing space is made available, some plant will eventually occupy this space. In ecology, this growing space is called a “niche”. Weeds are the pioneer species of ornamental landscapes and gardens By anticipating ecological processes, you can choose desirable plants that will occupy that niche instead of weeds. Perennial native grasses are a good choice for erosion control because they have fibrous root systems that bind soil together and will require little irrigation. Leaves and litter from grasses protect the soil from raindrop impact. Perennial grasses also increase soil organic matter and water infiltration rates. As roots die, the decomposing roots decompose and create voids that allow subsurface water flow. Grasses are usually classified as warm-season or cool-season species. This refers to the season in which they grow most readily. They are also classified into bunch grasses or sod forming species. Bunch grasses are frequently sold as ornamentals and create attractive accents in the landscape. Sod forming grasses spread horizontally through stolons (above ground shoots) and rhizomes (below ground shoots) and are preferable for erosion control due to their growth habit. Warm season species are best planted during summer and cool season species are best planted in the fall. Choosing the correct species for your site and soils is another matter. Different soil types can affect the success (or failure) of native grass plantings. Since native grass seed can be expensive, I recommend doing some research on the native species that are present in your area. In my landscape, I transplanted individual grass plants of desirable native species from elsewhere on my property to new locations. I provided some irrigation to help them for the first year. Once the seed has cured on the plant, I clipped the seed heads leaving behind the foliage. I spread the clipped seed heads in areas where I want that grass species to become established and stomp it firmly it into the soil surface. It works very well and over time, the various species have expanded in the niches they prefer. Next week, I will share some seed venders and grass species suitable for planting in the Verde Valley area. On another topic, don’t forget to enter your pecans in the Camp Verde Pecan and Wine Show Pecan Contest. Starting February 9, 2004, entries can be brought to the Camp Verde Chamber of Commerce or the Camp Verde Parks and Recreation Department. All samples must be submitted by 5 PM on February 12, 2003. For more information on preparing contest entries, consult the November 26, 2003 Backyard Gardener Column. It is available on-line at: cals.arizona.edu/yavapai/anr/hort/byg/. The University of Arizona Cooperative Extension has publications and information on gardening and pest control. If you have other gardening questions, call the Master Gardener line in the Cottonwood office at 646-9113 ext. 14 or E-mail us at mgardener@verdeonline.com and be sure to include your address and phone number. |