What to Prune in September

Jo.Baker
Published on September 22nd 2019
67
A view down a path flanked by evergreen hedges trimmed into arches.
As day length continues to decrease and the morning dew lingers into the day, my thoughts have moved onto the autumn tidy up. Although many plants are still in flower and showing off in the early autumn sunshine, it is the perfect time to get a few pruning jobs completed.

Evergreen

If you have any formally shaped evergreen shrubs, topiary or hedges, this is the last chance to give them a clip this year to keep them looking sharp and crisp throughout the winter.
Cutting back plants will prompt them to produce new growth. At this time of year, it will be a lot slower, but these new shoots do need enough time to harden off before the cold. Any later and there is a strong likelihood the leaves will suffer from frost scorching and discolouration.
Cupressocyparis leylandii: Hopefully you gave this very fast grower a cut back in June, as in September it should only need a much lighter pruning. Trimming the tips of the branches is sometimes referred to as shaving.
Other conifers can also be shaved at this time of year, but pick an overcast day to prevent the suddenly exposed under leaves from burning in the September sunshine.
There will be less bleeding of sap at this time of year, so your cutting blades won't clog up so quickly. However, I don't recommend the two swords method. Where was his PPE!
Prunus laurocerasus, (Laurel) hedges will also benefit from a trim at this time of year, but I recommend pruning with secateurs, as leaves that are sliced with edge cutters will quickly scorch and turn brown. Cutting back individual branches to just above a leaf will give a neater finish.
A laurel hedge alongside a tarmac drive in front of a house.
Cherry laurel makes a very quick growing hedge but needs regular clipping to maintain its shape

Deciduous trees

As a general rule, deciduous trees should not be pruned at this time of year. Let them absorb their energy and sap back down into the roots before doing any cutting back.
The exception is birch. As a profuse sap producer, cutting birches in spring and summer will result in a lot of bleeding, so now is the perfect time to shape your young trees by removing any lower branches. This will help to show off the white bark of the main trunk throughout winter.
Here are a few more tips on hedge cutting:

Shrubs

Shrubs which flowered in spring or early summer should have been pruned back in July or early August. This year's stems will produce next year's flowers, so pruning now risks having nothing next year.
However, shrubs that are flowering now can be cut back as soon as they've finished, as can some fruit bushes. Cut back a third of the plant by removing older stems just above a bud near the base of the stem.
Here are a few examples of shrubs you can cut back now:
Herbs such as lavender and rosemary can also be cut back now. As a general rule, don't cut back into old wood as it will be unlikely to regrow.
As usual, there are exceptions to this rule. Look into the middle of your plant and if you can see new buds forming near the base, then you can cut back.
If you are growing Berberis as a hedge, this spikey plant can take a light trim now to help maintain its shape.

Climbers

Climbers being trained over arches and pergolas will benefit from a tidying up to ensure you get flowers all over and not just on the top where we can't see them. On mature plants, carefully cut out a few of the old stems to encourage new growth at the base. Trim side shoots back and tie in new growth to replace the stems that have been removed.
Pileostegia viburnoides: If this beautiful plant is loving life in your garden and spreading out a little too far, you can safely remove whole branches back to the main stem at this time of year.
Pruning this lot should keep most of us busy for a while and will produce enough waste to fill your green waste bin several times over.
My only request, if you are getting anyone in to help, check they are insured, licensed and the waste is being disposed of correctly. An incorrect heavy prune at this time of year will take your tree, shrub or plant years to recover from.
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