Pareto on pruning

By Mike Clark, 27 March 2001

I hate books on pruning. I have a pet – and probably very cynical – theory, that on the basis that big books sell for more money than little books, gardening writers conspire to perpetuate the myth that pruning is complicated. And write big expensive books on the subject.

The simple fact is this. The Pareto principle very loosely applies to pruning. And I would prove it if I could remember exactly what the Pareto principle was. But if Pareto applied an 80/20 rule, then this is pruning on the Mike principle. Which is better at 90/10.

Ten percent of garden plants are a bit complicated to prune. Say, clematis and apple trees, for example. And pruning books make a meal of this. And ignore the fact that 90% of garden shrubs can be pruned without damage, by following a simple, basic rule.

When it has finished flowering, prune it; unless it flowers in late autumn or winter, in which case prune it in spring when the frost has passed.

That wasn’t too scary now, was it?

And if you accidentally use this rule on some poor specimen in the 10% category, don’t lose too much sleep. It is highly unlikely you will do any terminal damage. You may lose flowers for a year, or a little vigour. But plants are survivors. They won’t die if they can help it.

So why do we prune? Nature doesn’t.

Well, maybe nature does. In the wild, a spindly young plant throws a shoot up to reach the light. And along comes a rabbit, and nips off the shoot. What does the plant do? It throws up half a dozen more vigorous shoots from the base by way of replacement.

And that’s the first reason why we prune. To encourage thicker, denser growth. This is particularly true of hedges. I have a pretty long fuse, but I can get stroppy to the point of abusive with people who adopt the wrong approach to growing a hedge.

Do not, DO NOT (Grrr, Grrr) let the hedge grow up to the height you want it to be, and then keep taking the top off. You will regret creating a hedge with a few thin stems, gaps your neighbour’s Rottweiler could get through sideways, and a fluffy top. No, harden your heart. Cut your hedge back by half in the first year (there are exceptions, but remember we’re working on the Mike 90/10 Principle). Cut it back by a third in the second year. And in the third. And so on until, despite your savagery, it attains your desired height. Why? Because every time you cut back a leading shoot, several dormant buds will produce replacement shoots, and create the thick, impenetrable hedge you always craved. Yes, it will take a few years longer. But you can’t hurry nature. If you want an instant hedge, buy a fence.

Other reasons to prune? Well, these garden plants are ones which we have adapted from the wild to become garden ornaments. We want flowers. You have to understand a plant’s instinct to survive. Procreation is the name of the game. And a plant’s response to any sort of stress, is to produce flowers, and thence fruits, and thence babies. So cutting bits off a plant is to put it under threat, and its natural response is to procreate before it dies (of course it’s not going to die, this is horticultural gamesmanship). Therefore it flowers with all the enthusiasm it can muster.

We also prune to maintain a plant’s health. Because we have interfered with nature. We have cross-bred and hybridised, forever seeking better flowers, fruit, colour, whatever. But with scant regard for the plant’s natural resistance to disease. And disease, especially air-borne fungal disease, thrives in enclosed or congested places. So although we want vigorous growth, we must also retain an open shape to a shrub to allow air circulation. Hence the need to remove congested growth and keep the heart of a plant open.

Have I fallen into the trap I so despise? Have I rambled on and made it all sound complicated? Just in case, let me quickly get back to basics.

1. Cut out all dead wood, back to healthy growth.
2. Always prune to a centimetre or so above a bud. Because new growth will come from a bud, and any stem left above that will die, and provide an entry point for disease.
3. Alleviate congestion in the centre of the plant by removing any shoots which cross, or rub against other shoots.
4. If pruning to restrict size, on most plants (90/10!) you can cut back as hard as you like, but always follow 2. above.
5. Remember that the most vigorous new growth will come from the first bud below your cut. So you can determine where you want the plant to grow from.
6. If your plant is congested, prune to an outward facing bud. The new shoot will grow outwards instead of inwards.
7. The most common mistake is not pruning hard enough!
8. Don’t let them frighten you!

I wanted to simplify this subject for you. I’ve just read back over it, and confused myself. But I’ll let it stand. And if you’re none the wiser after reading this far, tell me and I’ll try again. I know it’s simple really, it’s just explaining it that’s complicated!