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Mahonias only require a light pruning to keep them healthy and in a good shape. Knowing when and how to prune your mahonia depends on the type of shrub that you have. The smaller border growing varieties need less pruning than the taller back-of-the border types. And both need to be pruned after flowering takes place. It’s also important to understand it’s not essential that mahonia is pruned and often do well when not pruned at all.
With over 70 different types of mahonia, it’s often difficult to know the best way to prune the particular one that you have. But mahonia shrubs divide roughly into two classes. Mahonia aquifolium are low-growing evergreens that flower in the spring. They only grow to about one metre in height and width. Mahonia x media is a taller and wider growing class of plant and is more popular in gardens. These flower at the beginning of winter, usually in November and December.
This article describes when and how to prune mahonia for each of these classes.
Mahonia aquifolium – short varieties
These smaller varieties of mahonia require only light pruning to keep them in trim. You can easily prune them just by deadheading the flowers after they’ve finished blooming. However, you can leave the old flowers on to feed the birds or to turn to seed for self-seeding.
If the stems are getting leggy or growing where you don’t want them to, prune them in stages. Sterilise your cutting tool and cut the branches a bit at a time back to the ground. But don’t remove more than one-third of any branch in each pruning session.
Mahonia x media – taller varieties
This class of mahonias grows upright and in long canes. You need to prune these unless you want them to grow to their full height of between 2m to 4m. Once again, pruning is best after they’ve flowered but in this case, that’s at the beginning of spring.
You need to have a pruning plan for a shrub this size. Prune one out of every three stems each year, cutting it down to 60cm above the ground.
General pruning rules for mahonias
Prune the mahonia as soon as it’s finished flowering. This plant can then develop new shoots and grow strongly.
Water well after pruning with an extra shot of fertiliser.
Thin out any crowded branches, especially the older ones in the middle of the shrub to increase air circulation.
If you cut your mahonia back to the ground, mulch around the base for protection.
Remove any new plant suckers that appear from the plant to keep it compact.
Remove dead or diseased branches immediately – with a sterilised cutting tool.
Never cut more than one-third off the length of a branch per year.