Roses need lots of care in dry, hot weather

gpointstudio/Thinkstock photo
gpointstudio/Thinkstock photo

The recent brief shower didn’t bring relief from the high temperatures and dry Santa Ana winds for either humans or plants. Fall is finally here? Doesn’t feel like it. The outlook is for high temps and maybe even triple digits.

Last month I gave illustrations and descriptions for mid-season pruning with a suggested timeline for pruning and restarting your feeding program. What may not have been clear is that this is a light pruning, and must be carefully calibrated with the weather conditions.

Specifically, when temps remain in the 90-plus range, you must take care not to remove too much foliage because this can over expose canes to the fierce sun and sunburn them, and can kill otherwise healthy canes or even the entire plant.

If you plan to have blooms to mark a special occasion later this year, it could take four to eight weeks from this pruning and feeding. Much depends on each individual’s program of irrigation, fertilization and the weather.

After pruning, restart your feeding program. Make sure the plants are deeply watered the day before. I recommend organic types and alternating with fish emulsions. This time of year, use a fertilizer that contains greater percentage of (P) phosphate in relation to (N) nitrogen and (K) potassium—that is, the middle number in the N-P-K formula on the box or bag will be the highest. This will enhance resistance to stress by encouraging a stronger root system.

If temperatures are in 90s or above, and you do not use organics, hold off fertilizing until weather cools down. If you use a fertilizer that is first dissolved in water, apply it right over the bush from top to bottom. A hybrid tea needs about 2 gallons of solution and that application should be watered in after a couple of days. If you use a dry granular product, be sure to scratch it into the soil surface around the base of the plant, and then water it in. Apply in the concentration recommended on label.

If growing in pots, use half the recommended amount, but apply it more frequently. Repeat your applications every two weeks. Liquid feeding with balanced water-soluble fertilizer allows for nutrients to be available to the plant now. Stop liquid feeding three weeks to one month before your typical first freeze date.

When temperatures continue to be in the 90s, it is necessary to ensure plants receive adequate water to stay hydrated. It takes only a few days in these temperatures without sufficient water for a bush to become seriously stressed and even damaged.

Because of California’s restrictions of water use, I suggest that with 3 gallons of water per HT twice per week a HT rose bush can survive. A layer of 4 inches of mulch will greatly reduce evaporation of soil moisture. This year the soil dries out more quickly than in previous years due to less water being applied as in previous years and, in general, the dryer soil environment.

With potted roses this is even more critical. Assess conditions every morning. Look for wilted or dry, crispy foliage. If you discover it soon enough, dousing with plenty of water may save the plant. If you wait to inspect until the afternoon or evening it may be too late or you might not get a good assessment of the plant’s condition: After a hot day, most plants can appear wilted while still receiving sufficient hydration.

Also inspect your irrigation system to make sure it is delivering enough water, isn’t clogged and isn’t over watering – all problems that come with age in drip irrigation systems. If an emitter is delivering much more or much less water than others on the line, it can change the system pressure and affect the other emitters. The simple solution: Replace it!

If a clay pot is used, more water is needed as the clay will absorb moisture from the potting soil and evaporate through the porous clay material. Plastic pots are better as they will not absorb moisture from the soil.

In any case, avoid staging potted roses on concrete that is exposed to direct sun, as that can heat damage their roots. Another possible problem with potted plants is the soil can pull away from the sides of the pot and water will just run through and out the drain holes in the bottom. This problem can be corrected by pressing the soil back against the inside sides of the pot when the soil is wet.

It’s not too early to start thinking about which roses you will remove and what you’ll replace them with. Go ahead and request catalogs from rose suppliers – they’re always available. Also, if you haven’t mulched recently, estimate the amount of composted mulch you’ll need in order to cover your garden beds 4” deep and plan to buy it for this coming winter or spring. An area 10 feet X 5 feet will require 4-5 cubic yards of mulch.

A common problem when hot, dry, dusty conditions prevail is spider mites. This topic was covered in a previous care column which you can find in the newsletter; look for Care for September 2013.

With warm days and cooler nights of fall weather be watchful for black spot and powdery mildew as well and treat as soon as detected. Now would be ideal time to plant roses while soil is warm and still time to settle in before colder weather. Do not heavy prune until after plant has experienced a dormant period, usually after cold nights of below freezing temperature.

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