As unpredictable as the weather has been lately, one thing we can plan historically is periods of intense heat in coming months. We had some samplings in recent weeks. We experienced temps in 90s-100s in June. As summer brings drier, hotter temps, roses will struggle to maintain hydration. It seems to me there has been more wind adding to the problem as well. I’ve noticed that my vegetable garden dries out quickly requiring added water. It is not easy to mulch vegetables.
For the past five years I have advocated a conservative style of summer rose care. From July to September, rose gardener activities in the desert – that’s us – can have a lower priority on your list. I believe it will be even more useful this year. I have read more articles suggesting this style of hot weather gardening for areas of high temperatures, like that of the southwest U.S.
When it feels as though Mother Nature is out to get us and the wind parches our skin, we have the luxury of removing ourselves. Meanwhile, our roses have no alternative but to stay where we put them. Roses don’t like intense heat anymore than most of us do. Their priority is to live. The plant will conserve its resources for roots, canes, leaves and blooms in that order. Blooms will be smaller with sunburned petals and lessened fragrance. Leaves will turn yellow as chlorophyll is degraded, reducing photosynthesis, and turn brown when they lose the battle to keep hydrated because transpiration can’t keep up. Roots will struggle to take up enough water to maintain transpiration from the leaves, and if the roots dry enough, they will actually shrink and lose physical contact with much of the soil particles around them. If your roses suffer desiccated leaves, do not remove them, as they will provide some shade to protect the cane from sunburn. Remember, if a leaf dies it is easily replaced; if a cane dies, it is gone.
Without saying, water needs increase dramatically in extremely hot and sunny conditions. Perhaps requiring daily watering. It is essential that you check soil dampness frequently during hot days. Use a water probe or stick you 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 for this method, use a small garden trowel to scratch down to that depth and check the moisture content. A minimum of 4 inches of good mulch over the entire bed will help conserve moisture and moderate soil temperature. You will be amazed at the difference it makes.
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 and pulls away from the container’s sides, causing water to run through rapidly, washing away soil and wasting water. Here are a few remedies to help struggling containerized plants: move potted plants to a cooler area under a patio cover or shade tree; never place containers directly 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; provide plenty of air circulation around the plants to allow cooling and apply three or four inches of composted mulch but not against the plant itself.
During hot weather, spider mites are a major destructive pest. They are hard to see because they 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 underside of the leaves. The 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 a complete infestation, remove all leaves within 8 to 10 inches 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 spray every few days.
My conservative style of summer care is borrowed from experienced desert gardeners. After the June and 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 only the petals helps prevent pest infestations and keeps the garden looking clean; it also allows the rose hips or seed pods to develop. This seed development sends a message to the rest of the plant to slow down, producing a short dormant period. It will relieve some of the heat stress on the plant. 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 and a higher water bill.
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.”
For more ideas, visit Temecula Valley Rose Society’s Rose Haven garden at 30592 Jedediah Smith Road in Temecula, as well as our web site at TemeculaValleyRoseSociety.org/index.shtml. Spread the joy of roses!