By James R. Feucht, Ph.D Colorado State University Cooperative Extension professor, Landscape Plants
If we think we get out of sorts during Colorado's cold winters, consider the poor rose bush.
Winter damage is common and Hybrid Teas and Grandifloras, the most sought-after of all roses, are among the most vulnerable varieties. Last winter took its toll on area roses.
If you are replacing roses that were lost during winter or if you are starting new plants, your best choice are roses already potted and available even in bloom at garden centers. Stored, bareroot and packaged roses probably are past their prime unless they have been kept in carefully controlled cool storage at the nursery.
To plant, prepare a hole at least 18 inches in diameter but no deeper than the soil ball. Mix some organic material, such as sphagnum peat or aged compost, into the soil taken from the hole but leave out any fertilizers. Fertilizers are salts and can hinder root growth as well as water uptake. The use of bone meal, sold widely in garden centers, also is questionable in Colorado. Bone meal may supply some phosphorus if your soil is acid. Chances are it isn't. Bone meal also supplies calcium. Most Colorado soils have abundant, if not too much, calcium.
Set the rose plant in the hole and place the soil, mixed with organic material, back into the hole; lightly tamp with the handle of a trowel. Do not pack soil too tightly. Add water until you are sure it has moistened the soil all the way to the bottom of the soil ball surrounding the rose.
Next, prune out dead stubs, weak canes and canes that cross over and rub each other. Keep, as many strong canes as you can. Wait to add any fertilizer until after the first peak of bloom. This will normally be late in June.
Roses host many pests. The most common early-season pests are aphids. Watch for them clustered on stems and near young buds.
As the season warms, spidermites may build up. These tiny creatures usually occur on the lowest leaves of the plant first and will be on the bottom sides of each leaf. To detect, hold a piece of white paper under a branch or some leaves and tap the leaves sharply. Mites, if present, will be visible on the paper as tiny moving specs.
To control both aphids and mites, use insecticidal soaps or simply syringe the plants with a strong stream of water weekly. The latter method is not recommended when rose buds are opening as it will cause mechanical damage to the flower petals.
As blooms fade on your roses, cut back to a point just above a 5-leaflet leaf. A new shoot and flowers will develop from the leaf base. Canes cut back to 3-leaflet leaves will fail to form shoots with flowers.
For more information about rose care, contact your local office of Colorado State University Cooperative Extension and ask for a fact sheet titled "Selecting and planting roses."
Photograph courtesy of Judy Sedbrook.
© CSU/Denver County Extension Master Gardener 2010
888 E. Iliff Avenue, Denver, CO 80210
Date last revised: 01/05/2010