By understanding how a plant responds to pruning, you’ll achieve your desired result
Houzz UK contributor and award-winning landscape and garden designer. Claudia de… More
Many people shudder at the thought of putting any sort of blade to a plant, but pruning will not only prevent a plant from growing too large and improve its overall look, it will also help a plant to stay healthy and produce more quality and quantity of flowers, fruits and leaves. It’s a huge topic, not one that could be covered in just one story (as each plant has its own needs), but this overview should equip you with some universal pruning facts, provide tips on tools and familiarise you with some useful terminology to help you get to grips with the basics of pruning.
Please, when pruning, do watch out for nesting birds.
Pick your tools
Choosing pruning tools can be a minefield, but it is important to pick the correct tool for the size of pruning cuts needed, or you’ll make the job more difficult. The last thing you want is to leave ragged stubs and invite infection into the cut stem. Here is a small selection of handheld tools to think about.
Most people are happy to use secateurs for pruning. There is a good variety to choose from, even left-handed versions are available and ratchet types, which are good for slicing through thicker stems. (The ratchet action means you don’t have to keep squeezing the handles for every cut you do.)
- Pruning knives
These have a curved blade, allowing you to keep the blade close to the branch as you cut. When choosing one, make sure it has strong and comfortable handles to hold and that it folds away for safety purposes.
- Hand or hedge shears
Use hand shears, which resemble giant scissors, for pruning jobs such as cutting down long grasses or lavender as well as for trimming hedges if you don’t want to use power tools for this job. They can become quite heavy if you’re tackling a lot of hedging, so pick ones with padded rubber handles for comfort and to absorb shock.
Loppers are long-armed versions of hand shears used for branches larger than half an inch across. As with secateurs, you will find the end of loppers shaped with either bypass blades, where the rolling action of one bypass blade passes the other when the handle is squeezed, or an anvil type, where the top blade bites down onto the lower blade for each cut.
There are various saws for larger and thicker bits of wood, ranging from handsaws to bowsaws, polesaws and chainsaws. Saws have either curved or straight blades with smooth or coarse teeth. Choose ones that have been forged from hardened steel, plated to resist sap and rust.
Remember to wipe all pruning blades with a cloth after use and check the blades are sharp. Plants pruned with sharp blades will heal faster.
Why we prune
Nature has a way of doing its own pruning – whether that’s branches falling to the ground, the shedding of bark or twiggy growth, or even animals such as deer and rabbits having a nibble (though perhaps not the plants we would want them to!).
However, for our cultivated plants we prune for shape, health, productivity and light.
It’s important to have a clear objective of what you are trying to achieve for the plant in question and to know how a particular plant will respond to being cut, so research well before wielding your blade. Here are just a few examples of ways in which we prune and the reasons why…
Deciduous trees and shrubs: we often prune these in the winter when the plant is dormant. By removing buds at this time, food reserves will be reapportioned to fewer buds and leaves when growing season comes around, and this will result in increased growth and vigour in the plant. It is also easier to see the shape of deciduous plants in the winter when the foliage has gone.
Summer-flowering shrubs: plants in this group, such as buddleja, fuchsia and perovskia, for example, are pruned in the following spring, which allows any new growth to mature and flower later on in the same year. If the plants are pruned in the winter, you risk any new shoots being damaged by frost.
All-year-round pruning: Despite the above, diseased or damaged branches should be removed as you spot them, which will encourage optimum healing to the wound. Also remember that smaller cuts mean smaller wounds – and, as such, quicker healing. On the flipside, larger cuts – although they require longer wound healing time – will cause more shoots to sprout out, something you’ll often see on trees that have been severely cut back.
Root pruning: this is often done for dwarfing a plant and is useful for indoor plants. If you do choose to root prune a houseplant, it is important to also cut back the right amount of shoots and leaves, as trimming the roots means a lower water supply to the plant for a short period of time.
Typically (but not exclusively), this type of pruning is carried out between November and March and stimulates new growth, but it will also mean the loss of flower for the season and sometimes a few years to come.
Just some of the plants that benefit from hard pruning include cotinus, berberis, spirea, lilac, dogwood, fuchsia, hazel, salix and ribes.
With hard pruning you remove quite a lot of the old wood, which can also be done with overgrown or old deciduous shrubs to provide new vigour.
For example, you prune lilacs, which flower on old wood, straight after flowering – around late May – after the plant has reached about six feet tall. Lilacs set next year’s flower buds almost immediately, so you need to prune about a fifth of the oldest wood to near ground level. Any renovation pruning can be done in the winter. If you have a large lilac, a tree perhaps, just remove old wood once the flowers have faded.
Dogwoods, or cornus, on the other hand, are hard pruned down to ground level in February or March to encourage bright-coloured stems for a beautiful winter display.
After pruning, make sure you mulch and feed the plants in the spring.
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Large and fast-growing shrubs such as philadelphus and forsythia need renewal pruning to encourage replacement of flowering shoots and the removal of old, unproductive dead wood, which tends to accumulate as the plant matures.
It is best to look at this form of renewal pruning as an extended deadheading as soon as the plant has stopped flowering. Cut out any dead or diseased wood and spindly shoots. If the plant is congested, remove some of the stems down to ground level. Then, after flowering, remove old flowered shoots down to strong young shoots lower down. Every year cut up to at least 20 per cent of ageing stems to near the base of the plant.
Other plants that benefit from pruning this way include plants that flower on last year’s growth, such as weigela, spirea and deutzia. Don’t prune roses or hydrangeas this way as you may unintentionally cut off this year’s blooms.
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With young trees from a year (these are called maiden trees) to those that are around five years old, formative pruning is done to encourage a clear stem and well-spaced canopy of branches. Young trees are sold as ‘feathered’, where the side shoots are attached and form main branches, and ‘un-feathered’ (these are generally cheaper), where there are no side shoots but a single stem.
Formative pruning of a young tree should be carried out when the tree is dormant between November to early March.
Where upright shoots threaten to compete with the leader (the main stem) of a central-leader standard tree, then a single leading shoot will have to be selected and the others removed.
If you are planting a young fruit tree, it is best not to let it fruit in the first year; this way, the plant will then put more energy into growing a better root system.
When looking at a tree in a nursery, choose one that is upright and doesn’t have all the growth on one side.
Although pollarding is not really a natural look, it is useful for certain trees and plants if you want to achieve a formal appearance, and it’s more often seen in European countries. Winter trees that have been pollarded resemble knobbly stumps with the trunk supporting a head of tightly cut stems and branches. The upper branches are removed, which promotes a dense head of foliage and branches that burst out in the summer.
Trees that lend themselves to this form of pruning include catalpa, tilia, robinia, London Plane, paulownia, liriodendron and salix and some types of acer. To keep your trees in shape, they will need an annual pollarding, just above the previous year’s cuts.
Don’t pollard trees in the autumn, as you may introduce fungi spores. This will lead to decay in the areas you have cut.
Avoid pollarding acer species in spring, as they will bleed – summer is better. (Bleeding, in this context, refers to sap leaking from a wound.)
Pruning groups for woody plants
What to prune when is a bit of a minefield with woody trees, shrubs and climbers.
These woody plants are each divided and subdivided into pruning groups, all helpfully defined by the RHS. Before you get out the secateurs, check the list as times of the year and pruning styles vary wildly, even within the same species.
Pruning groups is a topic I’ll return to in more detail in an upcoming piece.
For a very simple guide, you prune spring-flowering shrubs after they have flowered. For summer-flowering shrubs, you prune in late winter and early spring, which will promote new growth.
- Bleeding: the advice now on any bleeding from pruning cuts that have not been carried out at the correct time, is not to paint or bind the cuts but let them heal naturally by letting air in. Trees susceptible to bleeding include acers, birch, magnolia and poplar.
- Silver leaf: this fungus can affect trees including plum, apple and cherry, and also rhododendrons, roses and hawthorns during pruning. Remove any infected branches immediately and prune these plants in the summer months when active spores are less likely to be around.
- Coral spot fungus: to avoid this fungus, which can get into a tree or woody plant from pruning, make sure you prune any branches flush with the bough or trunk and don’t leave any snags. Dispose of all diseased branches straightaway. Never leave any leaves or dead wood to moulder, as it will run the risk of transferring fungal spores.
Do you have any pruning questions, disasters or successes to share? Start a discussion in the Comments section.