Regional Growing Guide: Southwestern Deserts
From the sunny beaches of California to the blistering deserts of the Southwest, this region is marked by nearly year-round sunshine and little rain. Roses bloom from April through December in the more temperate parts, while they take a rest during August and September in the great deserts, where searing temperatures vary little between day and night. There, roses have two seasons: spring and fall, with peak blooming in April and October. Ample irrigation is key. Soils may be alkaline or sand: it's important to amend with plenty of organic matter. The best roses are heat tolerant, and tend to bear darker leaves and bloom in more intensely saturated colors.
Select a season: Spring Early Summer Late Summer Fall
Planting Roses
The bare-root planting season is over in the low desert, although container-grown roses can still be transplanted through April. You want them to become established before summer's intense heat. If you're at a higher elevation, bare-root roses can be planted now and containers through May or until the heat hits. Dig a good-sized planting hole, about 18 to 30 inches wide and deep, to allow roots to spread easily through the soil. Mix fertilizer in the bottom of the hole, especially phosphorus to promote blooming. Make the sure the bud union, which is a raised bump on the stem where the variety was grafted to the rootstock, is about two inches above the soil line.
Clean Up Leaf Litter
Roses are relatively free of problems in the low desert, although they are susceptible to powdery mildew, especially in the winter months. This fungal disease can survive on leaf litter. Rake up any leaf litter that may have dropped after pruning in January and February before applying a fresh layer of mulch.
Mulching
Spread a 3- to 4-inch layer of organic mulch beneath plants. Mulch maintains soil moisture, moderates soil temperature, and keeps weeds at bay. As the organic matter breaks down, it adds nutrients to the soil. Use any combination of compost, grass clippings, dried leaves, bark chips, or shredded remains from your chipper/shredder. Spread mulch to the edge of the shrub, but keep it several inches away from the stem.
Watering Roses
Roses need regular water as they prepare for their spring bloom. Apply water at the edge of the shrub's canopy and slightly beyond. This is where feeder roots are actively absorbing it. Water should penetrate 2 feet deep through the entire root system. If you use drip irrigation, make sure it runs long enough to penetrate to that depth. Use a soil probe to determine how far water reaches. It will move easily through moist soil and stop when it hits hard dry soil.
Checking for Flower Thrips
Thrips are tiny insects barely visible to the naked eye. There are many thrips species, but the flower thrips that may be found in newly formed rose buds are a brownish color and about 1/8 inch long. To check for their presence, hold a piece of white paper beneath rose buds and tap. The insects will fall onto the paper. Thrips have rasping mouthparts, which cause only cosmetic damage to the flower, but it is usually not noticed until after the flower opens with brownish petal edges. Thrips are attacked by beneficial insects called minute pirate bugs. No insecticide is needed, unless you plan to exhibit in rose shows. If so, and thrips have been a problem in the past, spray an insecticide formulated for thrips on the unopened buds, not the entire bush.