Pruning Mahonia: when and how?

Which species of Mahonia are affected by pruning?

With Mahonias, no regular pruning is really necessary, especially for mature specimens.

In summary, it is mainly the taller Mahonias, between 2 and 3 m, that benefit from pruning (Mahonia x Media, Mahonia bealei, Mahonia lomariifolia…). This excludes the Japanese and Chinese Mahonias, which are quite different in appearance, with their fine, thornless foliage (Mahonia eurybracteata).

However, the Mahonia aquifolium, known for its holly-like leaves, remains fairly compact and can be partially cut back when used as groundcover.

Mahonia aquifolium at the top. Below left Mahonia lomariifolia and below right Mahonia x Media ‘Charity’

Why pruning a Mahonia?

Mahonias are part of the evergreen bushes with a relatively slow growth rate, but there are several reasons to prune a Mahonia, and some gardeners even recommend pruning every two years to stimulate the bush:

• On young plants recently planted to encourage branching and thickening of the bush
• For aesthetic value on larger Mahonias (Mahonia x media ‘Charity’, Mahonia bealei, Mahonia oiwakensis, etc.): by clearing the trunk at the base, the bark is revealed, enhancing the upright silhouette of the bush, from which the leaves and flowers seem to spring even more
• For Mahonia aquifolium, used as groundcover, to densify the bush and improve its shape, as well as to stimulate future flowering
• On an old specimen, to rebalance the branches and habit.

On the left, a well-layered flowering. On the right, the trunk has also been highlighted by removing the branches

When to prune?

Whatever the species of Mahonia, pruning should always be carried out immediately after flowering, typically in February, usually for Mahonia x Media or Mahonia lomariifolia. Pay close attention to the deflowering of your Mahonia, as it may bloom earlier during mild autumns. Pruning will then occur earlier.

When pruning at this time, you will miss out on the lovely fruiting of the bush, with its frosted blue berries, which birds are fond of in spring, but you will not sacrifice, on the contrary, future flowering.

Always prune during frost-free periods.

How to prune?

Equip yourself with gloves for all “spiky” varieties to avoid injury. For thin branches, a good pruning shear is sufficient, but for higher branches, use a branch cutter to make the task easier.

Pruning should be light on Mahonia, while still ensuring to remove dead wood from older plants.

An old plant

• Once the flowers have faded, armed with a pruning shear for the smaller branches, start by clearing the bush by removing its dead branches;
• Work from a distance to rebalance the dimensions and silhouette: a branch that has grown too high should be cut back to the height of the others for harmony. You may also want to stagger the flowering of the Mahonia a bit more: cut the branches at varying heights to achieve a flowering bush almost all the way up;
• If you wish to highlight the bark that often becomes bare after a few years, prune the branches growing from the trunk to at least 1.5 m in height for a sculptural effect.

On this unbalanced old Mahonia, we will proceed with a cut on 3 main branches that are growing too high.

A young plant

The aim is mainly to thicken it and increase its density: in the first few years, prune the branches at the tips, at the level of the last cluster of leaves to induce more branching. This is a kind of pinching that will densify the branching.

N.B.: There is also sometimes the question whether to prune the clusters bearing the berries? They are quite useful to birds in winter or spring and prolong the decorative aspect with their bluish colour. It is better to prune them once dried, when they no longer add value to the bush (unless you wish to make homemade jelly or liqueur).

On a well-balanced and healthy plant, the fruiting offers a beautiful spectacle in return!