MARCH 17, 1997
March rose care for bountiful summer flowers
by Mary Robson, WSU Horticulture Agent
As the weather warms, roses move into active growth and begin developing buds for summer. This is the perfect time to restore old roses or renew younger ones.
If you haven't pruned roses, do so now. Prune lightly on climbing roses and "old" shrub roses (sometimes called Antique roses, varieties such as "Rugosa Magnifica" and "Blanc Double de Coubert"). These roses must form a woody structure of canes that carry the growth of new buds. Trim back old damaged wood and thin out some canes to allow good light penetration. If a climbing rose is pruned to the ground, one or two seasons of bloom will be lost while it replaces the lost canes.
The newer "David Austin" roses, which have been hybridized from many different parents including Antique roses and newer floribundas, also require lighter pruning in their first years. They become rather bushy, upright plants with blooms on the terminal tips of the branches. Light pruning means leaving at least 2/3 of the wood, removing only about 1/3. Some of the "David Austin" types can grow to 6 or 7 feet tall and bloom more vigorously if most of the woody structure remains.
Most other common roses, such as miniatures, tree roses, hybrid teas, and floribundas, can take quite heavy pruning at this time of year. They are usually cut back to about 18 inches from the ground. Many gardeners have trouble doing all this cutting, but it's important to remove old growth and allow the plants to renew the wood. Don't worry about it. With good care, the rose will replace what's pruned away in this first clipping.
After pruning, rake away all old leaves twigs, cleaning the ground under the rose. Many rose growers use a fungicide spray just after pruning to help retard later rose disease problems like black spot and rust. This helps to control fungal spores left over winter on the canes and twigs of the plant. Growers interested in less-toxic control alternatives may want to look for a rose fungicide containing "neem oil," the product of a southeast Asian tree. It's been recently registered for rose use, and the label suggests that it may be effective against black spot, but relatively few gardeners have reported on its use in this area.
The final part of spring rose care involves using fertilizer. Roses need fertilizer when they are in most active growth, about mid-March through the end of July. The fertilizer helps supply nutrients for new cane, leaf, and bloom growth. One grower suggests that over 40 healthy rose leaves are necessary to support just one blossom. Without good leaf growth, bloom is sparse. Supply nutrients with either organic sources such as alfalfa meal, cottonseed meal, and bone meal, or use processed water-soluble fertilizers. The water-soluble types release nutrients in a form immediately accessible to the roots, but it's easy to burn plants by using too much of this type.
Organic fertilizers work more slowly and will not begin to work fully until soil temperatures warm, but they release nutrients slowly and reliably over a long period. Many rose growers rely on alfalfa meal as a slow natural fertilizers work well if used in connection with compost, which contains billions of the micro-organisms that help to break the fertilizer down into useable components that the plant can access.
Washington State University plant specialists do not recommend combination insecticides with fertilizer included. Use of these "combination" products results in applying too much insecticide and may harm beneficial insects. The roses benefit more from a careful fertilizer plan and selective insect treatments as needed. Spray aphids off with a stream of water!
Visit WSU's Agriculture Site on the World-Wide Web at http://www.cahe.wsu.edu.