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Index : Plant Care
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- 7. Caution When Selecting - Using Weed Killers - Top
- Just look at the shelves in garden departments and you’ll find them stock to overflowing with weed killers. But some of those products can be very dangerous for home gardeners to use. Not in terms of harm to people, pets or wildlife, but some of these products can be very harmful to valuable landscape plants. Chief among them are products containing a weed killer called Triox.
Triox is a total vegetation killer! It’s advertised for use on walks, driveways, along fences and other spots where no growth is desired. But read the label information and what you’ll find is that Triox will damage or kill any desirable plant who’s roots it comes in contact with! So applying Triox to a fence line, driveway, walk, or patio will surely allow this vegetation killer to move down into the soil where it is likely to contact underlying roots of surrounding desirable trees and shrubs. In addition, a heavy rain can wash the Triox from the area of application to surrounding areas causing additional damage. The bottom line for home gardeners - don’t use products containing Triox! Be very cautious using any product labeled, vegetation or brush killer. They’re likely to have similar harmful effects.
Another herbicide product that can damage trees and shrubs is the lawn weed killer - Dicamba. If tree or shrub roots are growing in your lawn area, and you apply Dicamba it too can be absorbed by tree and shrub roots, damaging these desirable plants. It’s common for mature trees to have roots that extend out as much as 4 times farther than the spread of the branches. Shrubs also have roots extending out well beyond the ends of their branches.
Fortunately, one of the most popular weed killers for home gardeners - Roundup - is relatively safe to use. It is not absorbed by plant roots and has no harmful effects in the soil, unlike Triox. It kills weeds by being sprayed on, and absorbed by, their leaves and other green tissue such as green stems. It moves from the leaves to the roots via the plants internal cambium tissue. Once it reaches the roots, it kills the entire plant.
Roundup is actually the well-known brand name for the chemical ‘Glyphosate’. It is available as the active ingredient in a number of herbicide products such for the control of perennial broadleaf and grassy weeds. It’s one of the most effective products for the control of certain hard-to-control woody-stemmed weeds such as our notorious Desert Broom.
The best way kill Desert Broom and other woody brush is by applying undiluted Roundup concentrate directly to cut stems at the base of the plant. This application should be made while the plant is actively growing. So, it’s best to hold off treatment until late March or early April. At that time, cut the stems of Desert Broom off close to the ground and immediately paint them with concentrated Roundup. The material will be absorbed through the cuts and transfer directly to the roots.
The product you select should have a concentration of at least 18% Glyphosate. The simplest way to apply the weed killer is to pour a small amount in a styrofoam cup and use a small paint brush to dip and paint the weed killer on to the cut stems. “Because of the potential for contamination, do not pour any left over Glyphosate back into the original container. Just use it up by applying it to the cut stems.
“Spring Fertilization of Gardens and Landscapes” will be the topic for this week’s garden demonstrations. They will be presented on Wednesday at 9 a.m. at the University of Arizona - Pima County Extension Center, 4210 N. Campbell Ave (central); and at 1 p.m. at the Wilmot Library, 530 N. Wilmot Road (east), and on Friday at 1 p.m. at the Oro Valley Library, 1305 W. Naranja Drive (northwest).
Garden centers and nurseries here in Tucson and throughout Southern Arizona stock a wide array of plants. Not all of them are well-suited to the desert. In fact, a large number of the varieties of plants for sale are not true desert plants and may require significant amounts of water to survive our harsh, often drought-stressed environment.
Before purchasing plants this spring, do your homework. Find out whether the plant(s) your thinking about purchasing are desert native, desert adapted or water-dependant exotic species.
Desert native plants will require the least amount of care. Once established these plants can survive on what Mother Nature provides in terms of water and nutrients. Even during periods of drought native plants will survive; either by going drought dormant or by self-pruning to reduce moisture loss. Prickly pear cactus shed their outermost pads. Palo verde drop leaves, stems, sometimes even branches to reduce their water needs.
There are a wide variety of Southwest desert natives to choose from. Selections of trees include; Blue, Foothills, and Desert Museum Palo Verdes, Arizona Rosewood, Catclaw Acacia, Texas Honey Mesquite and Ironwood. Some good choices of desert shrubs are; Creosote Bush, Chuparosa, Autumn Sage, Fairy Duster, Texas Rangers, and Brittlebush.
Desert-adapted plants are those able to tolerate our desert environment in terms of heat and drought tolerance. But during hot, dry periods they will require periodic irrigation. Selections of these desert-adapted trees include; South American Mesquites, Texas Honey Mesquite, Sweet Acacia, Western Soapberry, Gregg Ash, and Kidneywood. Some desirable desert-adapted shrubs include; Yellow Oleander, Red and Yellow Birds-of-Paradise, Emu Bush, Feathery Senna, Poverty Bush, Bush Lantana and Mexican Honeysuckle.
In addition to trees and shrubs for low water use desert landscapes, cacti and succulents are also great choices. Native Saguaro, Barrel, Hedgehog and Prickly Pear Cacti need little attention after establishment. Agaves are also great drought-tolerant plants for desert landscapes. Some of the best for home gardens include; Octopus Agave, Hauachuca agave, Twin-flowered agave and Holly agave.
For landscape color, there are many desert perennials to choose from. Those that can manage on just one watering per month during hot weather include; Penstemon, Angelita Daisy, Desert Marigold, Desert Zinnia, and Paper Flower. Perennials that need a little more frequent watering (every week or two) include; Peruvian Verbena, Calylophus, Chocolate Flower, Golden Dyssodia and Guara.
In general, plants that use the most water are annual flowers like petunias, geraniums, zinnias and marigolds. It’s best to limit the use of these flowers to a few pots for seasonal color on the patio. Summer vegetables like tomatoes are also high water users, so if your planting a garden, limit it’s size or grow your vegetables in containers.
When shopping at local garden centers and nurseries it’s best to avoid unfamiliar varieties of plants that don’t have the ‘desert look’. Plants with lots of large, soft leaves are probably not adapted to desert conditions. Many of these plants come from wholesale nurseries in California and are best suited to their milder growing conditions.
Consult reference books and internet sources for listings of additional recommended desert plants and their watering requirements. Among the best books to consult are: Landscape Plants for Dry Regions, by Jones and Sacamano; and Plants for Dry Climates by Duffield and Jones. An on-line data base of recommended desert landscape plants for Southern Arizona is available at: www.ag.arizona.edu/pima/gardening.
Written by John Begeman, College of Agriculture and Life Sciences, the University of Arizona,
520-626-5161.
- Updated: February 19, 2006
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