We said in last month's newsletter that choosing the right time to prune Arizona roses is difficult. Ideally, they should be pruned two weeks before the buds swell. Some gardeners simply "sense" when this is about to happen. (One St. David gardener judges it by when the mesquite trees begin to bud.)
In odd years, when cold winter weather never really settles in, there are few plants that follow their normal schedules. Two weeks ago my rose bushes began unfolding tender new leaves, apparently confident that spring had truly arrived. It took another burst of winter to convince them otherwise. Fortunately, the plants suffered little frost damage and frost damage is what we were trying to avoid by waiting this long to prune. Remember, pruning a plant that is not fully dormant can stimulate new growth at a time when that growth is still vulnerable to winter damage.
Now that March has arrived, we can begin looking forward to the last frost of the year (usually towards the end of this month, although it varies from year to year). It may not be wise to delay pruning our rose bushes much longer. Aim to have them pruned by the end of the month.
The main goal in pruning roses is to produce a plant with an adequate number of long healthy canes for an abundance of flowers every year. To accomplish this we need to remove dead and diseased wood, thin out weak or crossing canes, head-back the more vigorous canes, and generally create a healthier better balanced plant.
Severe or heavy pruning (cutting the plant down to three or four canes, 6-8 inches high) is not recommended in Southern Arizona because severe pruning exposes too much of the plant to the fierce Arizona sun and often results in short-lived plants. Some rose growers use heavy pruning to produce longer stemmed, show quality roses, but this can be risky unless you are willing to provide your plants with adequate protection.
Moderate or light pruning are better approaches for Southern Arizona rose growers. Moderate pruning thins the plant to five to twelve canes, 18 - 24 inches high (see Figure 1), and results in a larger plant that shades the ground and suffers less from heat injury. Light pruning involves only a minimum of cutting, leaving a plant 3 to 4 feet in height with only the nonproductive canes removed. This results in a profusion of showy, but short stemmed blossoms.
When deciding how to prune your rose plants, keep in mind that all healthy live canes will produce blossoms for 4 to 6 years (or even longer), but with decreasing quality of blossom. If an old, unproductive, or poor quality cane is left in the plant too long, it may be difficult to get new canes to grow up from the base of your plant.
To prune, begin examining the plant for diseased or dead canes. Cut these canes off at the crown, being careful not to leave a stub. If you are removing diseased canes, be certain to keep them away from any healthy canes, and dip your pruning shears in a bleach solution after each cut. Now, step back from your plant and consider its shape. Does it have weak or malformed canes or branches? Is it over-crowded by too many center canes? Would you like it to spread more or spread less? Are there canes that cross one another? Use your answers to these questions to help you decide which of the older canes to remove.
A word of caution: there is a wide difference in the growing habits of rose varieties. In general, rose bushes grow upright, but each rose variety will have different growing tendencies. Some varieties may produce longer canes and have a wider spread, and others are more compact with smaller canes. Floribundas are an example of this latter type. As in pruning trees, it is important to prune with your plant's natural shape rather than against it.
Check the new growth coming up from the base of your plant. Look for tall, slender, light green "canes" growing straight up from below the bud union. These are called suckers. They will not produce blossoms and should be removed as soon as they appear.
After removing the desired number of older or weaker canes, you will need to prune the top portion of your plant, referred to "header" cuts in tree pruning. If the top growth is allowed to become too thick, there will be little, if any, growth of new canes from the base of the plant.
As a rule, cut back new growth of canes by one-third, saving a few well-spaced side branches as well. Make your cut within one-fourth inch of a bud or side branch and on a slight angle opposite the bud, with the bud on the high side (see Figure 2). If you want a plant with a wider spread, cut right above a bud or side branch that faces out. To reduce spread, cut right above a bud or side branch that faces in toward the plant's center. Remove last season's leaves from any of the remaining canes. Immediately after pruning, you should seal all cut surfaces larger than a pencil with a sealing compound having an asphalt base. This will protect the fresh wood from infestation by borers.
(The Cooperative Extension has a pamphlet on "Roses for Arizona". Contact the Sierra Vista or Willcox office for a copy.)