Humboldt Rose Society

The "Why" and "How" of Rose Pruning... By Dr. Stan Baird

National Award of Merit winner

Yes, once again it’s that time of year when dutiful rosarians face the daunting task of pruning their roses. But those visions of a bountiful and colorful crop of exquisitely formed roses encourage us to venture forth with pruning shears in hand to brave the vengeful stabs from rose thorns - not to mention the aching backs and sore knees that accompany the pruning process for some of us!. But make no mistake - whether you are an avid exhibitor or grow roses for your own enjoyment, timely pruning is absolutely essential for a summer of glorious blooms and healthy bushes.

Before we start, we should make sure we have the necessary equipment: a pair of heavy leather gloves to protect hands and fingers from thorns, a pair of by-pass pruning shears, and a pruning saw. That is the bare minimum of equipment. Never use an anvil shears as this will bruise the canes badly. The upper blade on an anvil shears comes down on a thick, straight blade - thus the name ‘anvil’. The blades on bypass shears are curved and thus cut more cleanly without bruising tender new canes.

A pair of loppers is another useful tool which will often cut through large canes faster and
easier than a saw. Make sure both the by-pass shears and the lopper blade are sharp. A simple file and a small vise to hold the shears steady is all that is needed for sharpening your pruning tools. Perfectionists use a whetstone and make the process more complicated. If you have more than a dozen bushes, you will need to sharpen your by-pass shears periodically during the pruning process. A dull blade on your pruning shears will result in bruised canes and runs the risk of splitting the cane, so check the sharpness of your shears frequently.

For bushes with many canes that are close together, a pruning saw with a narrow blade about ½ inch wide is an ideal solution where there is no room for pruning shears or the standard size pruning saw. The Harlane Company, 266 Orangeburgh Road, Old Tappan, NJ 07675, sells a Japanese-made 5-inch folding pruning saw that is ideal for working in tight spots. When you’re though, you can fold it and stick it in your pocket. The last one I purchased cost $10.95. Or you may be able to find something similar at a local hardware store or building supply company.

You may also want something to seal the ends of the freshly cut canes to prevent the sap from bleeding and to discourage pests such as cane borers from entering the canes. Not everyone considers this important. Other growers dutifully seal even the smallest canes. Or you may compromise and seal only large canes of 3/4 of an inch in diameter or more. Tree seal is readily available but it tends to wash off in heavy rains and can get on your shoes and end up on the living room carpet. A somewhat tidier alternative is Elmer’s glue. Finally, if the ground is damp, you may want a pair of knee pads.

Why is the pruning process so essential to productive roses bushes? There are at least three reasons. First, pruning improves the health of the bush by removing diseased, unhealthy canes and old canes that are no longer productive. On bushes which are exuberant growers, thinning out the excess canes allows better air circulation. In an area where summer fog wets the rose foliage almost nightly, good air circulation helps to prevent fungal diseases such as black spot, rust, and mildew. Second, by eliminating canes judiciously, we exercise some control over the shape of the bush. Third, thoughtful pruning invigorates the bush and results in larger blooms of better quality. A rose bush that is left to its own devices will, in a few years, becomes a tangled mass of thin, spindly canes and small blooms of poor quality.

The novice rosarian is often intimidated by the many choices involved in the pruning process. But pruning may seem less daunting if we remember the three fundamental principles: (1) eliminate the old, unproductive canes and the small, twiggy growth, (2) cut the cane at an angle about 1/4 inch above an outside eye ( if the bush tends to sprawl, cut to an inside eye), and (3) remove canes in the center of the bush to improve air circulation.

Small, spindly canes are, of course, easy to recognize; but how do you recognize a cane that is too old to produce quality blooms. It is important to remember that new growth emerging from a thin cane will be no larger that the cane from which it emerges, so prospects for good bloom on the new growth are not encouraging. The bark of an old cane will be darker and rougher than that of the new vigorous canes which developed just last summer. The bark on an old cane will often have small breaks that provide a haven for fungi and insects. The bark on new canes will be either light green or in some cases, reddish and very smooth. On an established bush that has received good care, there will usually be an ample number of thick, healthy canes. In that case, it is usually possible to leave only canes that are at least ½ inch in diameter. But a new bush or a bush which is a weak grower is another matter. The leaves play an important role in the growth and health of the bush, so if removing all the thin canes will leave the bush with only one or two canes, the bush will suffer. In that case, it is advisable to leave some thin canes so that the bush will have an adequate amount of foliage for good growth.

The next question may be, "What is an ‘eye’ and how do I recognize one?" An eye is a small scar on the bark of the cane where a leaf was attached the previous year. If the leaf was large, the scar on the bark may be quite conspicuous. In other cases, we need to look closely to spot any evidence that a leaf once grew there. Look for a horizontal line (which may curve slightly) on the bark. Even though there is no bud to indicate that a new cane will develop at the eye, if the cane is cut just above the eye, the bud will usually develop. This is because of the bush’s natural tendency to put out buds at the highest point on the cane. Because of Humboldt Country’s mild winters, there may be old leaves on some of the canes at pruning time. If so, these leaves should be removed.

A problem that frequently perplexes the beginner is a young, healthy cane which has no evident eyes at the point where you would like to make the cut. Does the cane have a lateral - another cane growing out to the side? If so, the solution may be to cut off the lateral flush with the main cane. Do not leave a short stub as this is often where die back starts. Although it may not be evident at the time that you remove the lateral, in a few weeks there will be not one, but several buds develop around the scar where the lateral growth was removed. The cane will not be able to support that much new growth, so as soon as the new buds reach about a quarter inch in length, break off all but the largest bud. Resist the temptation to leave several buds as the resulting growth and the blooms it produces will be substandard. It is advisable to check your rose bushes every few days for several weeks following pruning. You may find some canes have too many buds emerging and some will need to be broken off. Sometimes after the new buds begin to develop, you may decide that a cane needs to be cut back a bit farther or perhaps removed entirely.

The other question which beginners often ask is, "How high should I prune my roses?" Unfortunately, there is no widespread agreement on the correct answer. However, there are some guiding principles that can be helpful. In mild climates such as Humboldt County, it is not necessary to prune as severely as in climates with sub-zero winters where winter kill is a perennial problem. The vigor of the bush is also a consideration. A vigorous bush can support more canes and be pruned higher than a bush that is only a moderate grower. However, an extremely vigorous
cultivar like ‘Futura,’ if pruned too high, can become so high by midsummer that you need a step stool to spray the top of the bush.

Before you start cutting, first study the bush carefully and locate the strongest, healthiest canes that you will probably want to preserve. First, remove the growth that is most obviously in need of elimination. Then study the bush once again to determine what other canes need to be removed, if any. Some cultivars, such as Marijke Koopman, a rambunctious but quite wonderful pink hybrid tea, produce so many new canes that it is necessary to remove some new, healthy canes in order to keep the center of the bush open and provide good air circulation. Marijke Koopman will continue to produce new canes with wild abandon, to the point where by midsummer there will be so many canes that they will need to be thinned out. There is a limit on how many canes the roots system of a rose bush can support. So how many canes should be left on a bush during spring pruning? This depends on the age of the bush and its vigor - or lack thereof. A new bush should have only three or four canes. But an established bush that is extremely vigorous may be able to support as many as five or six canes.

There are a few "don’ts" for pruning roses. Don’t use anvil type shears. Don’t leave crossing canes. Don’t leave stubs on either the canes or the bud union. Don’t leave more canes than the root system can support. Don’t leave diseased canes. Don’t leave forks at the end of canes. Grandiflora roses are pruned the same way we prune hybrid teas. For floribundas, climbers, and pillars, most of the same pruning principles
apply; but there are a few minor differences. Because floribundas tend to be shorter than most hybrid tea and are usually more floriferous, we can leave more canes once the bush is established. Cut the cane at the first outside eye below the point when the cane branched out to produce a spray. Climbers and pillars take longer to establish than hybrid teas, so pruning should be limited to removing thin, twiggy growth for the first two years. After the plant has an ample number of strong canes, remove one or two of the oldest canes each year; but avoid removing large numbers of old canes in one season.

While pruning, clean up the dead leaves around your bushes, for these leaves may harbor harmful fungi and insects. After pruning is finished and before new growth starts is an ideal time for a dormant spraying. The conventional wisdom is to use an oil sulphur mixture for dormant spraying. However, some very eminent plant pathologists recommend using the same fungicide and insecticide you use during the growing season. In coastal Humboldt County where roses can be subject to bacterial diseases, adding a bactericide, such as agricultural streptomycin, at a half teaspoon per gallon, is a proverbial "ounce of prevention" that is very worthwhile.

And now that your roses are all pruned and looking very tidy but a bit gaunt, take a moment to relish that feeling of smug satisfaction at knowing that your roses are well prepared for a summer of glorious blooms that will be the envy of all the neighbors! And while the number of canes our rose bushes produce in Humboldt County may make the pruning process more arduous, take consolation in the fact that rosarians from the frigid Mid West would kill for canes and bushes of that size - not to mention the color intensity and bloom size we get in our cool, mild summers!