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Index : Flowers - Perennials
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- 24. Roses in Summer Doldrums - Top
- Problems with summer roses in Tucson can be numerous. Intense sun, and baking heat can put tremendous stress on delicate rose plants, particularly hybrid teas. There are, however, some things you can do to help your roses along until cooler weather returns.
It's normal for roses to develop sun scorched leaves at this time of year. From a distance the foliage may appear to have a bronze cast. Upon close inspection, small brown spots or patches cover part or most of the leaf. These leaves will drop off as new growth develops in early fall. However, roses can be protected from direct sunlight in the summer by constructing temporary wood-frames covered with 70 % shade cloth. Position the cloth to provide shade from noon to late afternoon. Roses protected from afternoon sun will have deeper green leaves and larger blossoms.
Along with leaf scorch come the drying effects of heat, sun, and wind. Regular irrigation is a must for growing roses, especially during the warm months. Roses should be watered three times a week during the summer. We are having an active Monsoon season, so when rains do occur, regularly scheduled irrigation should be delayed until needed. To help conserve moisture, mulch the ground around roses with forest mulch or other wood mulch products. Pull mulch back slightly from the canes. A layer of mulch 3 inches thick placed around roses will not only reduce moisture loss, it will also keep the soil cooler and roots heathier.
In addition to the drying effects of sun and heat, roses are often damaged by a build-up of salts in the soil. This results in a browning or blackening of the tips or edges of leaves. Irrigation water contains salts as do fertilizers, and over time, salts can accumulate to harmful levels. Flushing these salts out of the root zone will eliminate the problem. The best time to do this flushing is during the Monsoon season. Allow your irrigation to run 2 or 3 times it's normal duration. All this extra water will dissolve excess salts and wash them down below the root zone of your roses. Flushing of excess salts should be done twice yearly corresponding to our Summer and Winter rainy seasons.
Some rose growers like to dead-head their blossoms during the summer. Dead-heading is the removal of spent flowers before they go to seed. It is beneficial from the standpoint of diverting the plants energy from seed production and redirecting it to new growth and flower production. Other rose growers choose not to remove spent blossoms. They contend that leaving the spent blooms on will slow growth activity and conserve the plants energy for fall production of flowers. Both opinions are valid. So if you prefer to have some blooms all summer long, then dead-head. If you prefer to have the largest possible flower display in the fall, at the expense of summer bloom, then do not dead-head. Note that when dead-heading, cut the blossom off with a sharp, scissors-action pruning shears back to just above a five-leaf leaflet.
It is not advised to fertilize roses during the summer months, but it may be necessary to add iron to the soil. Roses prefer a slightly acid soil and often become iron deficient in our highly alkaline desert soils. If young leaves are yellow, except for the leaf veins which remain green, then your roses are lacking iron. Apply chelated iron to the soil as directed on the label. Iron chelate may also be applied as a foliar spray to green leaves up in a hurry. Soil applications must still be made for longer lasting effect. Always purchase and use chelated iron. It's more expensive than other forms, but it's the only kind that works in our alkaline soils.
Finally, be careful when eradicating weeds around roses. They are sensitive to chemical herbicides. Even glyphosate, commonly sold as Roundup, can damage roses if even a small amount comes in contact with leaves or stems. If herbicides are to be used, apply them early in the morning when temperatures are cooler and the air is calm. Better still, use mulches to prevent weed growth and hand pull the occasional weed that pops up.
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Written by John Begeman, College of Agriculture and Life Sciences, the University of Arizona, 520-626-5161.
Material originally appeared in Arizona Daily Star gardening column, on August 01, 1999
- Updated: August 01, 1999
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