Now that March is with us it seems time to mention pruning. Because of the uncertainty over the future of the garden here I have not done much sowing yet but I have been pruning. Because pruning is the topic that confuses gardeners more than any other I thought a few words would be relevant.
Firstly, it is important to realise that pruning does not always keep plants small. Light pruning, especially in summer (August) can slow growth but harder pruning actually encourages and stimulates growth. We know that because we prune roses pretty hard in spring to stimulate new foliage and flowers. We do the same with buddlejas. So, apart from affecting the flowering of some shrubs, it is a mistake to think that hacking back a large shrub will make it smaller – plants usually balance their top growth with their roots and the top will soon bounce back to the same size or larger.
I would also make a differentiation between pruning and cutting back. Pruning is to benefit the plant while cutting back is for our benefit – to get it out of the way!
What to prune now
As a rule, spring pruning (in March) is restricted to plants that flower in late summer. When it comes to foliage you can prune away to your heart’s content because the new growth will be full of fresh foliage. The plants to concentrate on now are:
Roses – cut away the oldest growth and shorten last year’s growth
Buddlejas – prune hard – this applies to the common B. davidii types
Caryopteris – prune them back quite hard to get rid of old wood – same applies to perovskia
Hydrangea paniculata and H. arborescens – these need cutting back fairly hard if you want big heads of flowers. Lighter pruning will give you many more, but smaller heads.
So what should you leave alone?
Anything that is about to flower in the next two months, such as ribes, forsythia, kerria, camellias and early (mostly white) spiraeas. Leave them till immediately after flowering, usually in late April.
And clematis? Few plants cause as much confusion as these climbers but I think it is down to them being so widely planted and so varied. There are always exceptions but, basically the rules are:
Spring-flowering, generally small-flowered, such as C. alpina, C. macrophylla and C. montana – prune immediately after flowering if required.
Large-flowered, May and June flowering (the most popular) – prune now, cutting back the shoots to the first pair of fat buds, working back from the shoot tips. Retain a basic framework or you will miss out on the early summer display. Pruning and training can be tricky and slow since the shoots are brittle. If you do prune back hard it will not kill the plant but you will forfeit flowers this summer. You may get a display in late summer and you will get a good display the next year as long as you leave it alone.
Late-flowered, Viticella and Texensis types. These generally have smaller flowers, but lots of them. These can be pruned back hard, to 30cm or so, now, because they flower at the ends of this year’s stems, just like a buddleia.
Shrubs that can be damaged by winter frosts, such as choisya, hebes and hardy fuchsias are best left till next month, once the worst of the winter weather is over (hopefully), and then they can be lightly pruned and any damage cut away.