- Mark Cullen: The right time to prune plants
- Pruning shrubs
- Why prune shrubs
- What to do
- Watch video
- Plant-by-plant deciduous pruning tips
Mark Cullen: The right time to prune plants
People ask me this time of year if they can prune many of the plants that went unnoticed in their gardens up until recently. When the leaves fall attention is drawn to evergreens, shrubs and trees on the property.
The short answer is that you can prune almost anything this time of year without damaging the plant.
Permanent or “woody” plants like cedar hedges, boxwood, yews, junipers and the like lend themselves very nicely to a late-season haircut.
It gets a little tricky with flowering shrubs, especially if you want to maximize the flowering potential of the shrubs on your property.
As a rule of thumb prune fall flowering shrubs like Rose of Sharon, late flowering hydrangea and Buddleja (Butterfly Bush) at any time in the fall. Early spring flowering shrubs like forsythia, purple leaf sand cherry, crabapples and the like should be pruned in late spring after they have flowered, or in the early summer. The buds that will produce the flower come spring have already formed, so pruning them now means taking the risk of diminishing the plant’s flowering potential next spring.
Perennials generally should be cut back in the spring. Allowing the sturdy flowering plants to remain standing over the winter invites song birds in search of the seed as a food source. These plants also add some winter interest in the garden. Soft-stemmed perennials like hosta and peonies are best cut down in the fall and the cut portion put in your composter.
Finally, roses generally are cut down come spring unless there is a risk of them breaking in the winter due to heavy winds.
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Why prune shrubs
Shrubs create the structure in a garden so it’s important to keep them in good condition with regular pruning. This will improve a plant’s shape and encourage flowers and fruits.
What to do
How and where to cut
- Pruning cuts are essentially wounds to the plant where disease could enter so use sharp, clean tools and make clean cuts without leaving snags. Cut close to buds, but not into them, and always above.
Pruning young shrubs
- Early pruning helps establish a shapely shrub with vigorous, balanced growth.
- Most evergreen shrubs do not need thinning or formative pruning. However all shrubs benefit from shortening any excessively long shoots and cutting out weak or damaged growth.
- Deciduous shrubs are more likely to need pruning into shape; this is known as formative pruning. Young shrubs often grow lots of shoots so you will have to thin them early on.
- Correct lopsided growth by lightly pruning longer shoots and hard pruning weak stems.
Rejuvenating old shrubs
- Shrubs such as forsythia and buddleja can soon accumulate masses of old, dead wood in the centre if they are not pruned regularly.
- The best way to rejuvenate these plants is to cut them back during the dormant season.
- First cut out dead, diseased and crossing stems, and then thin the number of remaining stems by half.
- Shrubs that respond to severe pruning, such as ribes and philadelphus, may be cut almost to ground level to re-establish a framework of new shoots. If the shrub is old and it’s hard to predict a successful revival, take cuttings just in case.
Pruning shrubs in pots
- Once a container shrub reaches maturity it is usually best repotted annually in spring, or every other year, using the same or similar sized container.
- If you find the plant is very pot-bound, this is a good time to lightly prune the roots.
- Prune about one-third of the thicker non-fibrous roots back to the intact rootball, but avoid damaging the fibrous feeder roots.
- Repot in fresh compost and finish by pruning the top growth by about one-third to balance the root loss.
Coppicing and pollarding shrubs
- Shrubs grown for their colourful stems or foliage, such as dogwood, need to be cut down every spring to 4-5 buds to encourage new growth.
- This is known as coppicing. If you want to keep a framework of older stems, cut down one-third of stems.
- A similar technique is called pollarding where stems are cut back to the same point a single stem or framework of stems. This is often seen on London plane trees and can be used on eucalyptus. After pruning, make sure you feed and mulch the plant.
Pruning shrubs in autumn
- After a summer’s vigorous growth, it is a good idea to give your shrubs a light prune in the autumn to keep them in shape.
- Once deciduous shrubs lose their leaves, it is easy to see the plants’ overall shape and decide what needs to be cut back.
In this video Colin Crosby, the superintendent of woody ornamentals at RHS Wisley, prunes dogwoods and willows in spring to encourage new growth.
Plant-by-plant deciduous pruning tips
- In mid-spring cut back last year’s shoots to one or two pairs of buds from the base.
- Remove some older branches if the bush is overcrowded.
- Hard prune to ground level in late winter to stimulate next year’s foliage, or remove one-third of stems in mid-spring for a display of fine young foliage and attractive flowers.
- If grown as a dwarf hedge, clip in late-winter and mid-summer although you will get fewer berries.
- Prune after flowering, shortening all young green growth by up to two-thirds, but avoid cutting back into the old wood.
- After flowers have faded, thin out one-third of the branches to improve shape and next year’s flower quality.
- Between late winter and mid-spring, trim wall-trained bushes to shape, cut out weak growth and shorten new shoots to encourage branching.
- In late summer, cut back new growth on fruit-bearing stems.
- Cut back shoots after flowering to a pair of leaves below the flower-head.
- In winter, prune weak branches back to their base, remove suckers and thin out older branches.