Growing roses in Arizona's heat can be tricky, but with proper care, roses can live and thrive in Arizona gardens. Although the punishing heat and a period of humidity in mid-summer can make things challenging for gardeners, Arizona's sunny climate is beneficial to roses. Proper maintenance, especially careful watering and feeding, is the key to growing roses successfully in Arizona. Purchase roses from a local grower, and they should be able to withstand Arizona's extreme summer heat.
Water roses deeply to develop a strong, sturdy root system. Water slowly so the water penetrates the soil around the roots, then push a steel rod or a long screwdriver into the ground to be sure the water has penetrated to a depth of at least 18 to 24 inches. Don't water again until the top 2 inches of soil are completely dry. In Arizona, this may mean watering your rose daily during hot weather.
Spread 3 to 4 inches of mulch such as compost, shredded wood or straw around the base of each rosebush, then replenish the level of mulch as it blows away or decomposes. Mulch prevents soil moisture from evaporating as quickly and keeps the roots moist. As the mulch decomposes, it improves the quality of the soil, as Arizona soil is often clay-based or sandy.
Prune roses in late January or early February, as new growth appears early in Arizona's mild winters. Remove any weak, broken or diseased canes, or canes that cross over other canes. Each cut should be diagonal and should be made 1/4 inch above an outward-facing bud.
Fertilize roses every six weeks during the growing season, as roses grown in Arizona's climate do best with frequent light feedings of a slow-release fertilizer, rather than one larger feeding. Feed the rose immediately after pruning in late winter, then repeat every six weeks until early June. Withhold fertilizer during the summer, then give the rose light applications of slow-release fertilizer in September and mid-October. Look for rates of application on the fertilizer label, then give your rose half of the suggested amount. Always water your rose immediately before and after feeding.
Spray your roses with cool water on hot mornings to increase humidity around the plant. Spray early in the morning, as the hot sun magnified through the water droplets can burn the leaves.
Check your roses for insects and disease every day. Fungus can be a problem when Arizona's humidity rises during the summer months. Watch for powdery mildew, which looks like powder on the foliage and blooms. Prevent powdery mildew by keeping the area around the rose clean and free of debris. Water early in the day so the water can evaporate. If necessary, treat roses with a fungicide. Roses in the desert sometimes suffer from an iron deficiency, which causes the rose's leaves to turn yellow. Iron deficiency can be moderated by applications of iron chelate. Aphids are tiny green bugs that leave a sticky substance on the foliage and buds. Remove aphids with an insecticidal soap or an insecticide.