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British Trials Show It Produces More Blooms
By RNRS President, Ken Grapes

When next you are at our Gardens at St. Albans, do leave time to see the various cultural trials which are now in progress, while bearing in mind that some of them will take a few years to provide concrete evidence of their efficacy or otherwise.

Many people, both within and outside the Society, are aware of the pruning trials being carried out in association with the Consumer's Association, and involving, in the case of one group of plants, pruning with a hedgetrimmer.

The results to date (and we are now into the third year) are, to say the lease, surprising. But these trials are as yet by no means conclusive. Quite apart from their intrinsic value, trials make us reassess accepted practice and can be very thought-provoking. Appraise them yourselves.

Garden Trials Began In 1990

In spring, 1990, the Consumer's Association set up a trial in conjunction with the Royal National Rose Society at St. Albans, to investigate whether the time-consuming traditional method of pruning roses is really necessary. Our trial was carried out on established beds of four varieties of large-flowered (Hybrid Tea) roses and four cluster-flowered (Floribunda) roses.

We pruned one third by the Traditional method, being careful to observe all the rules, such as cutting to outward-facing buds and thinning out overcrowded stems.

Another third was rough pruned, by cutting all the shoots straight across with pruning shears at the same height.

The rest were pruned with a hedgetrimmer.

The initial results aroused a lot of interest. Rough pruning and hedgetrimmer pruning both induced stronger growth and an equally good or, in many cases, better flowering performance than traditional pruning.

However, after just one growing season we could not say whether these easier pruning methods would be free of longer-term problems. So we decided to keep the trial going. Last year, we repeated the treatments and our rose experts assessed the bushes in September.

The differences between the treatments were not quite so marked, but, overall, the results were consistent with those of the previous year.

Rough Pruning and Hedgetrimmer Pruning again induced more growth and better quality growth than traditional pruning.

With the Floribunda Roses, the blooms were again bigger and more numerous after Hedgetrimmer and Rough Pruning. With the Hybrid Tea Roses, all three pruning methods gave good blooms.

Traditional Pruning Method

All stems were pruned just above outward-facing buds with the cut sloping down away from the bud. Dead or damaged shoots were cut back to healthy wood, and the centers of the bushes were thinned out, if overcrowded. Old or weak stems were cut back to a quarter of their length, or removed altogether.

Stems of the large-flowered (Hybrid Tea) roses were cut back to at least half their length. The cluster-flowered (Floribunda) roses had some old stems cut back to within a few inches of the ground, whilst new shoots growing from the base were only lightly pruned.

Rough Pruning Method

The shoots were all trimmed with pruning shears at the same level, and all the cuts were roughly horizontal. We did not worry about whether the cuts were above a bed, or not. Each rose was trimmed to the same height as the traditionally pruned block in that bed. Any dead wood was removed.

Hedgtrimmer Pruning Method

Roses were cut to the same height as above, using a hedgetrimmer. No dead wood was removed. The hedgetrimmer cuts were very ragged, leaving lots of snagged and ripped shoots.

Dieback Not A Problem

Traditional pruning methods for roses were developed centuries ago, when most varieties were susceptible to dieback. These pruning methods have been passed on from generation to generation, without question, ever since.

However, rose breeding has come a long way, and many modern varieties don't suffer badly from the effects of dieback, because they are so much more vigorous.

Dieback can affect new growth beneath the visibly damaged stems, causing thin, weak shoots. These shoots produce fewer flowers, which are smaller, and less well shaped than on normal plants. The weaker shoots are also more susceptible to diseases such as blackspot and mildew, and they can bow over and sag under the weight of flowers.

Our trials showed that Rough Pruning and Hedgetrimmer Pruning caused no more dieback than traditional pruning.

The Trial Goes On

From our initial results, rough pruning, or using a hedgetrimmer seems to give better short-term results than traditional pruning.

However, we do not advise that you switch pruning methods until we bring you more long-term results. It is possible that roses which are roughly-pruned may become overcrowded in the center, and therefore more prone to diseases. Traditional pruning encourages the development of open-centered bushes. It may therefore be necessary to alternate between Rough or Hedgtrimmer Pruning and Traditional Pruning. We shall keep you updated on any new developments as they occur.

Other Trials Underway

Although many Brit "purists" have foamed at the mouth, this particular trial has achieved terrific press coverage and general interest. We feel that the National Society should be doing this sort of thing on behalf of rose growers and, indeed, this is but one of a series of trials now underway.

Tests are also in progress at St. Albans to compare ways of combating soil sickness, to evaluate different planting practices and different mulching materials (over 20 are being tried) and to assess disease resistance in a spread of varieties.

Enthusiasts will keep this last-mentioned trial under particularly close observation. The varieties in question are not sprayed but are otherwise given normal cultural treatment.

This article was originally published by the Royal National Rose Society, in conjunction with the British Gardening Magazine, "Gardening From Which?" It was reprinted in the "American Rose" Magazine, August 1992.

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