Growing Roses - June 2, 2010
Jeff Schalau, Associate Agent, Agriculture & Natural Resources
University of Arizona Cooperative Extension, Yavapai County
Contrary to popular belief, roses are easy to grow and can produce many fragrant, beautiful flowers throughout the growing season. Getting healthy stems, foliage, and flowers requires irrigation, fertilization, and proper pruning. Overall, the Verde Valley’s climate is ideal for growing roses and you don’t need to have a formal rose garden to enjoy them. Most people grow hybrid tea roses, but there are many other types of roses including hybrid perpetuals, polyanthas, floribundas, grandifloras, climbers, miniatures, shrub-types, and more.
Roses need some soil moisture year round and regular irrigation during summer. Drought stress leads to defoliation and sunburn of canes while overwatering or poor drainage may lead to disease problems and/or nutrient deficiencies. Water can be applied through overhead, drip, or flood irrigation. It is critical that the water go deep (1½ to 2 feet) into the soil. Check the soil moisture with a long screwdriver to determine irrigation frequency - it should always be moist one inch below the surface. Deep watering twice per week is usually sufficient during the hottest times of year. Organic mulches will also help conserve water and keep roots cool.
Roses respond favorably to periodic fertilization during the growing season. You can purchase rose fertilizers and simply follow the label directions. A less expensive alternative is to apply ¼ cup of 8-8-8 or 10-10-10 per plant every two to three weeks starting two weeks after the plants leaf out and continuing through September. Be careful not to get the fertilizer on the canes and water it in after applying.
During the flowering period, remove spent blossoms to promote new flower shoots. Remove faded flowers by cutting below the stem to just above a five-leaflet leaf. Prune all canes to a 30- to 45-degree angle above a live leaf, leaving no more than ¼ inch of stub above the leaf. Remove any dying or dead stubs throughout the year to discourage the carpenter bee, a small pith borer that nests in tunnels bored into rose canes. If this insect is a serious problem, seal the ends of the pruned canes with common white glue which discourages the bee from boring a hole down the center of the canes.
Dormant season pruning of established roses varies with different rose types. For all roses, remove all dead or diseased wood. On established hybrid tea roses, prune to produce an open center and direct growth outward from the center. A standard practice is to remove up to 1/3 of the oldest canes and leave some younger canes to replace the old ones that were removed. Healthy canes produce blossoms for 4 to 6 years or even longer, but canes 1 to 2 years old usually produce the highest quality, longest stemmed blossoms.
The major rose pests in our area are aphids, thrips, and powdery mildew. Some rosarians rely heavily on pesticides. However, I recommend that some level of insect damage be tolerated. Aphids can usually be knocked back with soap sprays or spraying with a high-pressure hose.
Flower thrips are tiny, winged Insects about 1/20 inch long. They affect the buds and blossoms of roses, some other flowers, and deciduous fruit trees. Thrips are said to prefer light-colored blossoms, such as yellow and white. Their damage can readily be seen as discoloration of the petals and distortion of the bloom. During severe infestations, some blooms will not open normally due to the insect's damage. If you are looking for perfect roses, you may need to use a systemic pesticide (such as acephate or imidacloprid). Once temperatures have risen above 90 degrees F, thrips begin to decline and their damage becomes negligible.
Powdery mildew is a fungus and it appears as a whitish coating on leaves and young shoots, curled leaves and distorted buds. This disease can be largely prevented by planting resistant varieties in sunny locations. Overhead sprinkling may actually reduce the spread of powdery mildew because it washes spores off the plant; also, if spores land in water, they die. Fungicides are only effective when applied as a preventative treatment.
Below, I have included links to additional information. Also, use Twitter to follow the Backyard Gardener – see the link at the Backyard Gardener website (cals.arizona.edu/yavapai/anr/hort/byg/).
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 email@example.com and be sure to include your address and phone number. Find past Backyard Gardener columns or submit column ideas at the Backyard Gardener web site: http://cals.arizona.edu/yavapai/anr/hort/byg/.
Troubleshooting Problems with Roses, University of Arizona Cooperative Extension
Growing Roses, New Mexico State University Cooperative Extension Service
Our Rose Garden, University of Illinois Extension
Roses: Selecting and Planting, University of Missouri Extension
Roses: Care After Planting, University of Missouri Extension
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Last Updated: June 21, 2010
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