By Joel M. Lerner
Special to The Washington Post
Saturday, June 5, 2010; E01
In 1986, the rose, official flower of the District of Columbia, became the national flower of the United States as well. It's also the official blossom of Georgia, Iowa, New York and North Dakota -- making it most popular choice for a state flower. But this popularity is somewhat curious, as gardeners know roses are fraught with disease and insect problems.
With proper cultural conditions, roses offer beautiful flowers. We have had those conditions so far this spring: low humidity, cool temperatures and ample rainfall followed by drying winds to discourage fungus. And roses had great snow cover for winter protection this year. You can build on this optimal setup by following these cultivation practices so that roses remain healthy -- and flowering.
-- Give them the best soil. Roses thrive in a light-textured, friable planting medium. Dig the planting hole to a minimum of two feet deep and wide. Then mix two-thirds native soil to one-third compost or manure in the hole. Remove the rose bush from the pot and set it into the soil mix, being careful not to disturb the small, wiry absorption roots. Place the rose so the roots are in the ground and the base of the trunk is at ground level. Be sure that grafted roses are planted with the graft scar above ground. Protect the plants with mulch in winter.
-- Protect them from deer, which like to eat roses. Commercial repellents use animal products, such as putrescent egg solids, to make the plants unappealing to deer. Most repellents remain effective for about 30 days. Two products that I have tried with success are Liquid Fence and Deer Stopper. Deer don't like strongly scented plants, so mint and rosemary are deterrents, as are plants with fuzzy (tomentose) leaves. Installing a deer fence is another option. It should be eight feet high. In some jurisdictions, a six- to seven-foot fence is the maximum. In that case, plant evergreen shrubs or conifers on each side of the fence, creating the illusion of a wide area, so that deer are afraid to jump over it.
-- Water carefully. Roses prefer moist, deep, well-drained soil. The soil moisture is sufficient now, but if the D.C. region has a drought, roses would need deep watering at their base once or twice a week. Keep water from splashing onto the leaves of the plant to control leaf fungi.
-- Prune roses before growth begins in spring. Cut out old canes with thick stems and all deadwood. Clean pruners with bleach after using them to cut dead or diseased wood, before you use them on healthy canes. Lubricate pruners with light oil to discourage corrosion.
-- Add a fresh layer of ornamental mulch only after you have removed the old mulch. One to two inches of decorative mulch is all you need. Too much can impede air and water penetration.
-- Maintain weed-free beds. Pull existing weeds. Apply a pre-emergent weed killer in late fall and late winter. One safe material is a corn gluten meal powder that keeps seeds from germinating. It's sold under many names. A few I am familiar with are: Granulated Wow! Pre-Emergence Weed Control; Organic Traditions Corn Gluten Weed Preventer; and Planet Natural Corn Gluten Meal. Use the material in freshly weeded beds for best results. and water it in if used over mulch. As always, follow label instructions.
-- Spread an organic rose fertilizer around the base of the plants once a year, in spring. Espoma Rose-tone is one commercial product with a good balance of nutrients. Many rosarians have their own organic recipes; fish, banana peels, dried alfalfa and liquid kelp are a few.
-- Boost plants' immune systems with Employ Plant Health Promoter. Plant Health Care changed the name of this product from Messenger to Employ and added an immune booster. The company claims to have improved the original product and named it Harp-N-Tek. Employ is not a fertilizer, growth stimulant or enhancer, pathogen or pesticide. It's a Harpin protein -- a natural protein that activates a plant's self-defense system to respond to the presence of disease. Harpin proteins build strong plants that are able to resist broad spectrums of viral, fungal and bacterial diseases. Once the plant's defense system has been triggered, Harpin proteins quickly disintegrate, having never entered the plant and leaving no detectable Harpin residue. Employ is a natural product, but is not certified USDA Organic.
These guidelines are applicable to all roses, but some of the free-flowering, disease-resistant groundcover roses and tough native varieties do not need regular fertilizer or Harp-N-Tek.Breeds apart
Thousands of rose varieties have been bred over thousands of years. Even the latest hybrids were introduced from about 12 original species. Rose breeders can produce almost any characteristic they desire. The line between categories blurs with each new introduction. The greatest difference among them is flower, color, length of bloom and plant size.
Shrub roses are the hardiest and most disease-free, growing 4 to 12 feet high and wide. They grow together to form hedges or ground covers. Lower-growing shrub roses, two to three feet tall, have been developed.
Hybrid tea roses were bred for fragrance and color. They grow 3 to 6 feet high. New flower buds will form on stems when flowers are pruned. Cut stems to the first strong leaf (one with five leaflets). They usually need regular attention to discourage leaf spot, aphids and Japanese beetles. The best fungus protection is good air circulation that will dry the foliage quickly.
Floribunda roses are a derivation of hybrid teas, but the plants are shorter and more compact, and their flowers are in clusters instead of individual blooms. They were introduced in the 1940s, are considered easy to grow, and their shorter form fits well into landscape designs. Always purchase disease-resistant plants.
Grandiflora roses are usually tall, slender plants that can grow 5 to 6 feet tall, blooming on long stems. They have the grandest, largest flowers of all the roses, blooming in summer. If you prune flowering stems to the first healthy leaf before the petals drop, they will provide a second flush of flowers.
Climbing roses grow with long, arching canes. They do not really climb, but grow stems that look best trained on fences, trellises or arbors. The canes must be attached to the structure with string or wire. The roses will bloom two or three times by August, after which they can be pruned back to the main canes forming their framework. Leave these long canes for further plant growth in the next season.
Old-fashioned, or heritage, roses are direct descendants of the original species roses -- such as alba, damask, moss and rugosa -- and are recognized by the American Rose Society as those grown before 1867, the year the first hybrid tea was launched. They were introduced from Asia before 1600.
Miniature roses are diminutive forms that have been bred to mimic their full-size counterparts. They require the same care, but take less room. Some have good disease resistance; others require regular treatments to stay healthy.
For more information on rose care, locating special varieties, or other questions, contact the American Rose Society (http://Ars.org), the Arlington Rose Foundation (http://Arlingtonrose.org), or the Potomac Rose Society (http://Potomacrose.org).
Joel M. Lerner is president of Environmental Design in Capitol View Park.