By Cindy Watter, U. C. Master Gardener of Napa County
There were some benefits to the lavish rainfall we experienced this winter and spring. First, Napa residents got proof that the flood-control project worked. Second, and just as important to a rose gardener, the frequent rains washed off all the aphids that like to prey on emerging rose buds.
In addition, the roses appreciated the rain and responded with an explosion of bloom, climbing over fences and up trellises, filling borders and yards, and making a walk in the neighborhood a decidedly enjoyable experience.
Alas, this riot of scent and color was followed by a three-day heat wave that caused many roses to burst into bloom all at once, and then droop and fade soon after. What can the home gardener do to revive roses and coax them to bloom again?
First, recognize that some old (often called "heritage") roses bloom only once a season, while the typical ever-blooming rose can keep up a display into fall. Sharpen your clippers and deadhead your roses. I am serious about the sharpening, as working with dull clippers is an arthritis-inducing chore.
Roses that bloom only once should be pruned at the end of the growing season. Other types should be pruned in winter, at the end of the dormant season. However, all roses can benefit from a light pruning for shape. Remove weak or crossed branches, especially on the inside of the plant, and any suckers that emerge from the rootstock.
Remove any leaves that show signs of disease, such as black spot, rust or fungus. Clean up fallen leaves. To avoid spreading the pathogens, do not put diseased leaves in your home compost pile.
Black spot (Diplocarbon rosae) is a fungus that attacks leaves and stems, leaving them yellowed and covered with black marks. To minimize it, plant roses where sunlight will dry them quickly after watering. If you use a fungicide, apply it after the leaves have been watered, so it stays on for a while. For nontoxic control, Sunset's Western Garden Book recommends a spray composed of 2 teaspoons of baking soda and 2 teaspoons of horticultural oil dissolved in a gallon of water.
Rust (Phragmidium mucronatum) is another fungal disease that leaves rusty-looking pustules on the underside of leaves. Powdery mildew (Podosphaera) looks like talcum powder coating leaves, stems and buds. The University of California's "Rose Pest Notes" recommends a garlic-based or copper soap fungicide for rust. This product also works for powdery mildew, as does the baking-soda spray. Always wear gloves and follow package directions when applying fungicides.
The abundant rain has also encouraged weeds. Pull them before they develop seeds. Weeds can harbor pests, and they compete with roses for water and nutrients.
Fertilize roses after each bloom cycle. A dry fertilizer dug into the ground will encourage repeat flowering.
Sunset's Western Garden Book recommends dehydrated alfalfa pellets for a burst of nitrogen. Local nurseries carry other rose fertilizers. Follow package directions. After fertilizing, apply a thick layer of mulch to keep the roots cool, retain moisture and discourage weeds.
After I attended a U.C. Master Gardener rose-pruning workshop last winter, the presenters gave me a rose bush that had probably been untended for decades. They had salvaged it from a lot destined for the bulldozer. I used it for another pruning demonstration, took it home, planted it and left it alone. I was rewarded with an abundance of creamy white roses with pale pink centers. So far, my rose is perfectly disease free. The experience reminded me of the main point of home gardening: to work outdoors but relax on occasion and enjoy the results of your work.
Workshop: U. C. Master Gardeners of Napa County will hold a workshop on “Rose Care” on Saturday, June 3, from 10 a.m. to noon, at University of California Cooperative Extension, 1710 Soscol Avenue, Napa. The first spring blooms have faded, and many roses are beginning to show stress in the form of black spot, rust, mildew and aphid infestation. U.C. research-based help is at hand. Bring your questions. Online registration (credit card only); Mail-in registration (check only or drop off cash payment).
Master Gardeners are volunteers who help the University of California reach the gardening public with home gardening information. U. C. Master Gardeners of Napa County ( http://ucanr.edu/ucmgnapa/) are available to answer gardening questions in person or by phone, Monday, Wednesday and Friday, 9 a.m. to Noon, at the U. C. Cooperative Extension office, 1710 Soscol Avenue, Suite 4, Napa, 707-253-4143, or from outside City of Napa toll-free at 877-279-3065. Or e-mail your garden questions by following the guidelines on our web site. Click on Napa, then on Have Garden Questions? Find us on Facebook under UC Master Gardeners of Napa County.