Rose Care FUNdamentals for July 2013
by Frank Brines, ARS Consulting Rosarian
For the third year now, I have been practicing and advocating a conservative style of summer rose care. The Temecula Valley often has very high temperatures July - September. Temperatures can hover between the high 90s to 100+ for days and even weeks. Rose care activities fall lower on your priority list when you get the sense that Mother Nature is trying to kill you. These temperatures are enough to make any gardener want to escape to the beach, pool, or air conditioned room-anything but laboring among the thorns, battling bugs and soaking in sweat!
Roses don't like intense heat either. Gardeners who live in the desert-that IS us, you know-can verify that the number and size of blooms fall off dramatically in high temperatures. In addition, as plants struggle to stay hydrated, their fragrances diminish. When roots can't take up enough water, their leaf tissues dehydrate and burn to a crisp. Chlorophyll is depleted, causing yellowing and suppressing photosynthesis. The plant will conserve its resources for roots, canes, and leaves in that order. There is plenty of debate over whether to remove or retain desiccated leaves, some arguing that they provide shade for the canes. That may be so-and it's also a nice excuse not to crawl around in the hot sun stripping off leaves. And remember: If a leaf dies, it is easily replaced; if a cane dies, it's gone!
Without saying, water needs increase dramatically. Perhaps requiring daily watering. It is essential that you check soil dampness frequently during hot days. Use a water probe or stick your finger to a depth of four to six inches (that is, if you have fluffy soil OR unnaturally long fingers)! If your soil is too compacted to do this, use a small garden trowel to scratch down to that depth and check the moisture content.
Potted roses are even more susceptible to heat and drying because soil in a container will heat up rapidly, virtually cooking the roots. In addition, the soil contracts, pulls away from the container's sides, causing water to run through rapidly, washing away soil, and wasting water.
A few remedies to help struggling containerized plants:
- Apply three or four inches of composted mulch.
- Move potted plants to a cooler area under a patio cover or shade tree
- Never place containers on concrete or other surfaces that readily absorb heat from the sun-but if you must, use pot feet or other methods to provide an air space between the container and the surface
- Position light-colored umbrellas and/or shade cloth over the plants as I have done
- Be sure you provide plenty of air circulation around the plants to allow cooling
During hot weather, spider mites are a major destructive pest. They are hard-to-see that live on the underside of leaves and rasp the tissue. Left alone they can quickly defoliate a bush. Heat increases their reproduction. Look for "dirty" yellow stippled leaves and, in severe cases, webbing on the leaves. Leaves closest to the ground are usually the primary ones affected. Don't spend a lot time looking for the tiny insects. A quick light brushing of the underside of the leaf with your finger will readily support your suspicions: the surface will feel like it's covered with a fine grit. To help prevent an infestation, remove all leaves within 8" - 10" of the ground surface.
Roses enjoy a good shower (just as we gardeners do!) especially after a hot day. The difference? Give roses an early morning shower before the sun gets too high and the temperatures are hot for long periods. Jets of water can blast off dirt, dust, and even tiny pests (such as mites, mildew spores, aphids, etc.), and hydrate your roses in preparation for a hot day. If you use a water wand aimed upward to spray the underside of the lower leaves you can dislodge spider mites. Because they reproduce so quickly you must do this every few days.
My conservative style of summer care is borrowed from experienced desert gardeners. After the June/July bloom cycle, let the plant go into a mini-summer dormancy by removing only the petals, not the hips. (In other words, don't deadhead.) removing the petals helps prevent pest infestations and keeps the garden looking clean. Allow the rose hips (seed pods) to develop. This will send a message to the plant to slow down, producing a short dormant period. This will relieve some of the heat stress. Continue to supply sufficient water and check your system daily: One broken sprinkler head, clogged emitter, or chewed drip tube can result in a dried out struggling plant.
Above all, do NOT fertilize during hot periods-even organic Nitrogen can burn the roots of a stressed plant. As I always say, "Roses are like people: When it's hot, they want lots of water and heat relief rather than food."