One of the common reasons for plants not flowering is that they were cut back at the wrong time of year, and therefore emerging flower buds were cut off. At North Leeds Garden Design we find that people often come to us with questions about this and other queries about pruning: which plants need pruning, how do I know what time of year is best - and why do we do it at all.
So in this blog I want to dispel the mystique about pruning. Most of it is actually pretty straightforward and not something to be scared of!
What is pruning?
Simply put, pruning is when we cut away plant material. The most common reason for this is to maintain the current size of the plant and prevent it getting too big for the space allocated. This is, after all, why you give your hedge an annual trim – it’s certainly not for the fun of it!
However you would also prune if you need to:
- get rid of diseased stems or leaves, or stems rubbing against each other which can open them up to disease
- improve the shape of the plant – for example to stop it overhanging another plant, or to open up the centre of the bush to allow more air to circulate
- promote further bushy growth – since most plants will respond to pruning by putting out fresh shoots at the site of a pruning cut, and many herbaceous plants will also respond by developing new buds and flowers.
Pruning plants with a structure – shrubs
If you are new to gardening, or have moved into a house with an existing garden, you may have problems getting started in identifying what plants you've got. But what you can see is whether the plant has a permanent, year-round twiggy structure.
If so, it is a shrub or tree. If it has more than one (or occasionally two) main upright bare stems from the ground, then it is a shrub not a tree!
Now you have identified your shrub you need to work out when it flowers. If you're not sure exactly what it is, then the simplest rule of thumb is to prune it soon after it has finished flowering. Garden shrubs such as spiraea, weigela and philadelphus all flower in early summer, from stems grown the previous summer and autumn.
These plants can put on a lot of growth in summer and it’s very tempting to cut the new stems away when you have a tidy-up in the autumn. Be warned: if you prune these later than July you will get few or no flowers next year!
Those shrubs which flower after mid-summer will usually flower on the current season’s new growth; buddleia (aka butterfly bush) is a good example of this. These plants can therefore be pruned early in the year, before they start into growth.
Depending on your latitude and the weather conditions, you may be able to prune in February, or it may be best to leave this job to March. Just keep an eye on the plant you want to prune and the weather forecast! NB it’s always best to check your gardening book for specific advice on your plant, or go to the RHS website www.rhs.org.uk which has useful help on plant identification and on pruning.
Cutting back herbaceous perennials – flowering plants
These plants grow up and die back down into the ground each year, so they have no permanent twiggy structure. They include some of our loveliest garden flowers, including things like Michaelmas daisies, asters, day lilies, catmint, lambs lugs, perennial geraniums, rudbeckias, penstemons and a host of others.
Because they die right back into the ground each year after flowering, strictly speaking these plants don’t require cutting down or pruning. However, you will prolong flowering on many of them if you cut back individual stems as soon as they’ve flowered. Penstemons for example will continue flowering from June right up to the October frosts if you do this.
You may also have heard of the ‘Chelsea chop’. This is when slightly lax perennials, such as nepeta, are cut back around the time of the Chelsea Flower Show in order to promote later but more abundant flowering on shorter, stronger stems. Intrigued? There’s more about the Chelsea Chop at https://www.rhs.org.uk/advice/profile?pid=594.
Herbaceous perennials with a strong structure, such as eryngiums, cardoons and thistles, and sedums looks great for months after flowering. Their stems and seedheads dry out, and they gradually fade into autumnal shade while maintaining their shape well into winter. Many grasses, such as miscanthus and stipa gigantea, also continue to look beautiful, especially in winter sunlight. These plants all give you an extra season of interest - so should definitely not be cut down until the winter gales blow them over.
Pruning fruit bushes and trees
Ok, now we’re into a more specialist area! If you have a fruit bush or small fruit tree, they may need pruning from time to time, especially as some fruit trees need annual pruning to promote fruiting. Pruning rules for fruit are more complicated than for shrubs - for example, plums generally fruit best on branches two years old, and they also need to be pruned quite late in the spring too. So do your homework first and get the specific advice for your fruit tree from a good gardening book or use the Advice section of the RHS website. After all it would be a shame to lose all next years’ fruit crop!
At North Leeds Garden Design we look after several client’s apple and plum trees and it’s very satisfying to see them growing healthily and cropping well from year to year. Here’s a recent picture of one of our small wall-trained apples ‘Discovery’ looking particularly fruitful!
If you feel your larger fruit or garden trees need pruning I would recommend using a qualified tree surgeon. They have in-depth knowledge of trees and their environments and can advise about the best action to take which will safeguard the long-term health of the tree. They also have the skills and equipment to prune your tree safely.
I hope this has been a useful introduction to pruning. In my next blog I’ll explain more about how exactly to go about it, what equipment you’ll need and what to consider before you start.