Roses are heavy feeders and they need a boost after surviving our grueling summer and to support fall bloom. Use a slow-release, dry fertilizer formulated for roses or flowering plants. Local rosarians also recommend dissolving 1 teaspoon of chelated iron in water to inhibit iron chlorosis, which is somewhat common in desert soils. This deficiency appears as yellow leaves with green veins. After 6 weeks, fertilize with liquid fertilizer every other week up to December. Stop fertilizing during winter. Fertilizing promotes tender new growth, which is susceptible to frost damage.
Keep Roses Well Watered
Water immediately after fertilizing. Water should penetrate 2 feet deep for established roses. Use a soil probe to determine how far water reaches. Any long pointed piece of wood or metal will work. Wait 1 or 2 hours after watering for water to seep through the soil. The probe will move readily through moist soil but stop when it reaches dry, hard soil. Once a month, water deeply to leach salts beyond the root zone. Salt build-up can cause salt burn on foliage and eventually death of the plant.
After clean up, spread several inches of fresh organic mulch around the base of the shrubs. Allow 2 or 3 inches of empty space around the stem, so that wet mulch doesn't contact the stem tissue. Mulch moderates soil temperatures, maintains soil moisture, and inhibits weed growth. As mulch breaks down it adds nutrients to the soil. Use compost, well-aged manure, dried leaves, straw, cottonseed hulls, or chipped matter.
Apply Epsom Salts
Roses are somewhat susceptible to magnesium deficiency in the low desert, which appears as yellowing on older leaves, reduced leaf size, and dead white tissue evenly distributed on both sides of the leaflets. The leaf edges cup down. Magnesium deficiency also may appear as dark brown or purple splotches in some varieties. To prevent it, apply 1/4 cup of epsom salts (magnesium sulfate) three times per year in September, January, and June.
Choose New Varieties
Bare-root roses are planted in December and January in the low desert. Do you want to add a particular color or fragrance to your rose garden? Start perusing catalogs, books, and Websites for varieties that interest you. Visit the fall rose shows held by garden clubs or go to demonstration gardens to see and sniff up close and personal. Ask your local nursery if they will carry the varieties you want. If not, order them online to arrive in time for planting. Choose those with high AARS ratings because those plants have been tested in a variety of conditions and are most likely to thrive.