Temperatures this fall remained warmer than average until just 10 days ago. Our roses were gorgeous and full-size, and the bushes were still producing vigorous new canes and new buds. Winter in the central San Joaquin Valley lasts only eight to 10 weeks, from mid-November until late January. Roses will need a little encouragement from us to enter dormancy as quickly as possible this fall.
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Pre-pruning roses or giving them a light shaping and cleanup in late fall not only makes winter pruning easier but will help force earlier dormancy. Cut off all new buds now and remove any canes that cross through the center of the bush as well as any suckers growing from the bud union at soil level. Dead wood and broken canes should be removed. New buds and growth on carpet roses can be sheared off with a hedging tool. You’ll see lots of dead wood in the interior of carpet roses; remove as much as you can now and clean out entrapped leaves and debris. Finish pruning roses in late December or early January.
Now comes the hard part. Strip off all the leaves. Hand-stripping is a real chore, but the easier way to strip the leaves is to wait until they turn brown and use a blast of water from the hose to knock them down. Rake up all fallen leaves and debris around the roses regularly to remove hiding places for pest insects and their eggs as well as fungal spores for black spot or powdery mildew.
When all the leaves have been removed, spray roses with a lightweight or all-season horticultural oil. So-called dormant oils have a heavier weight and because they are less refined can sometimes burn plant tissues. Dormant oils are no longer used. All-season horticultural oils will work well to control for pest insects and fungal problems. If your roses have had persistent problems with powdery mildew, common to roses planted in shady spots or irrigated with overhead sprinklers, try spraying the very effective, old-fashioned baking soda/oil mix:
1 tbs. baking soda
½ tsp. liquid soap (as a sticker/surfactant)
1 gallon water
1 tbs. ultra lightweight horticultural oil
Mix ingredients together in a spray applicator and spray to drench the canes on leafless dormant roses. Soak the soil around the base of the rose bush, as well. Do not store this mixture. Dispose of it according to the horticultural oil label instructions.
Bare root roses or young, fully dormant roses packed in sawdust or in a temporary planting medium should be arriving in local nurseries and garden centers in the next couple weeks. Approximately 40 percent of all roses grown in the U.S. are grown in the Valley. The selection of bare root roses available to us is impressive. Bare root roses are cheaper than container roses and are easier to transport and plant. The only drawback to buying bare root roses is that you can’t check the exact color or the fragrance. Check with local nurseries first since they tend to carry roses best suited for this climate.
More about buying bare root trees, bushes and berry canes in next week’s column.