A weed is any plant growing where it is not wanted. But we want plants in the desert, don’t we? Sure, but even in the desert there are a number of invasive and troublesome weed species.
Take the case of the salt cedars (Tamarix pentandra and T. aphylla). When first imported from Eurasia, around eight decades ago, nursery folks thought it would make a great, quick-growing landscape tree. It did. But it escaped.
And the salt cedars invaded riparian (moist) habitats across the West. The invasive salt cedar proceeded to push out all other plants in an estimated one million acres. This tree also salts the soil surface so nothing else grows, quickly forcing out all the plants that native wildlife depend on. Instead of diverse ecosystems, there is now a silent monoculture of salt cedar across acres of land. This shade-providing tree also fits the definition of “weed” – certainly a plant growing where it is not wanted.
The problem does not end there. A real hot topic is buffelgrass (Pennsetum cilare) and fountain grass (P. setaceum). Literally hot. These two grasses spread by seed along roadsides and onto desert hillsides. They crowd out native plants and dry into fuel for wildfires. These fires are fierce and hot. Native desert plants cannot stand “hot” fires and they often die.
Especially susceptible is our stately saguaro and most other cacti. Meanwhile these invasive grasses quickly resprout after a burn. As these grasses take over the desert they fuel even larger fires and reduce native plant and animal populations and diversity even further.
Sorry to say that buffelgrass was introduced by our government as a slope stabilizer and cattle forage, while fountain grass was introduced by the nursery industry as a graceful ornamental. Buffelgrass is on its way to being banned as a noxious weed, but fountain grass continues to be promoted by some landscapers, landscaping books and magazines. Meanwhile, there are many other graceful, yet non-invasive grasses that can be planted instead.
The public has an intense thirst for new plants. As a homeowner you know that there is a certain appeal to having something new and different in your yard. Nurseries are constantly on the lookout for new plants to slake this thirst. If there is a new plant or better selection available, nurseries will vie to be first to the market with it. But now the Arizona Nursery Association has voluntarily adopted a policy on invasive plants to reduce the potential for new plant introductions that invade our native environment.
One of the most newly discovered invasives is the African sumac (Rhus lancia). It threatens the desert landscape by growing in washes where it diverts channel flow, further eroding the landscape. Often natives growing at the edges of washes are toppled and killed. Rhus lancia seeds prolifically. It is also spread by suckers, displacing the native mesquite, a critical food source for numerous wild animals, including quail. Responsible nurseries no longer offer this invasive plant.
How about the innocuous African daisy? Such a pretty wildflower, right? Wrong! It is another plant with inedible seeds that spreads out into the desert. It sprouts earlier than our native wildflowers, such as Arizona poppy, then out-competes them and our other beautiful spring wildflowers for the available water. It isn’t just the beauty of our native flowers that is lost, it is also the food for the native animals and the diversity of the entire ecosystem that is threatened. You can still find seeds in wildflower mixes that are not from Arizona-based companies.
There are many other examples of invasives I could cite. Instead, I will ask you, as neighbors in this fragile Sonoran Desert environment, to be a good neighbor. Become knowledgeable about what you should plant. Don’t plant a pest – grow native!
Jacqueline Soule, Ph.D., has been writing about gardening in the Southwest for close to three decades. Her latest book, “Father Kino’s Herbs: Growing and Using Them Today” ($14.95), is available at area nurseries. Or email firstname.lastname@example.org for more information.
For more information
The Gardeners of Tucson will feature a guest speaker who will present information about the Arizona Native Plant Society “Don’t Plant A Pest” program this Tuesday, Aug. 9, at 7 p.m., at the City Ward 6 Council Office. 3202 E. First St. (one block east of Country Club, one block south of Speedway). The free meeting starts promptly at 7, with refreshments and a door prize drawing after the presentation. The public is always welcome, and there is free on-street parking.