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Simply Gardening
by Doug Green
Pruning: Cutting Through the Confusion

Jan. 25, 2000 -- One of the things I mentioned last week was how hard I pruned my roses and what that did for them. I'd like to explain a bit more about pruning this week and see if I can clear up any confusion in your mind about pruning plants.

Pruning is not very hard to understand. The reality about plant pruning is that there are only two kinds of cuts you can make. It doesn't matter whether we're talking roses or trees or geraniums, there are only two kinds of cuts and if I can learn them, why so can you.

To simply our life, let's call them a thinning cut and a heading cut. A thinning cut removes a plant shoot at the place where the shoot started out as a bud. No matter how large or old the shoot, from a geranium to a tree limb, a thinning cut will take it back to where it first started growing as a bud. A heading cut is a cut to any other part of that shoot. As long as it doesn't take the shoot back to where it started as a small bud, it is a heading cut. Now, that is pretty simple isn't it? If you cut it back to where it originally started growing -- its thinning and if you cut it anywhere else, its heading.

So, thinning cuts take a shoot back to where it started and the result of this kind of cut is to reduce the growth of the plant. If we cut a geranium shoot back using a thinning cut; no new growth will come from that shoot or from the place where it occupied on its mother shoot. Similarly, with tree pruning if we use thinning cuts, no new growth will come from that location. It is essential in pruning or repairing fruit or ornamental trees to understand this difference. If you use a heading cut on a fruit tree, you'll be left will all kinds of new growth coming from the buds below the cut. Broom-like growths from the end of branches are symptoms of poor pruning practices.

Let's return to geraniums. If we cut the end off the geranium shoot using a heading cut, this kind of cut will promote the growth of new shoots from all the leaf axils (the place where the leaves join the stem). If you want your geraniums to be bushy, you use heading cuts. If you want to thin it out and shape it a bit, you use thinning cuts. At this time of year, we would likely be using a lot of heading cuts on the geraniums so they will produce new shoots. We could then cut those new shoots off (using more heading cuts) and root them in water. The geranium would be further stimulated to produce more shoots and before you know it, we have a windowsill full of rooted cuttings waiting for spring. Heading cuts will give you new shoots while thinning cuts will reduce growth.

In the case of last week's roses, we want several things to happen when we prune them. We want to control their growth direction and we want more blooms. So, we use a heading cut to whack off the old spent rose flower. We take this cut at least 12 inches down the cane to an outward facing bud. This outward facing bud will start growing outwards and away from the dense centre of the plant. Because we've left several good buds on the shoot (remember this was a heading cut and not a thinning cut to take all the cane off to where it started as a bud) it is likely that several of these will start growing. Where we had a single blossom shoot, we now have several new ones coming. Some will undoubtedly grow up through the middle of the plant and will be candidates for a thinning cut after they have finished blooming.

The interesting thing about a plant is that the harder you cut it -- in other words, the more of the end you take off with a heading cut -- the more the lower-placed dormant buds will be stimulated to grow. When we take a twelve or eighteen inch heading cut to remove fading flowers, we'll stimulate more new growth than if we used a four inch heading cut. As a rough rule of thumb, you can take up to 30% of the existing growth off with each pruning to stimulate new growth. More than that might damage the plant, less than that and the plant is not stimulated to its maximum flower capacity.

So, with plants that bloom on new growth such as roses, geraniums and most annuals, feel free to make a heading cut that takes off up to 30% of the shoot length. The harder you prune your annuals, the more new growth they'll produce. And, we all know that the more new growth these plants produce, the more flowers that follow. You have to prune to get flowers.

It's just about time to start pruning the overwintered geraniums to stimulate new growth for taking cuttings. These cuttings will produce next summer's dreams and isn't it nice to know you can start your dreaming now.

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