Last updated on April 25th, 2022
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If you are growing a Mahonia shrub it’s important that you keep it healthy and well-maintained. One of the things you should do to help it remain healthy and grow well is to prune it.
Pruning the Mahonia aquifolium – Oregon Grape / Mountain Grape
Firstly there are two different classes of Mahonia. The first is called Mahonia aquifolium and these are the lower growing evergreens that flower in the spring. These smaller Mahonias typically don’t grow more than one metre in height and spread.
They require very limited pruning unless you plant them in the wrong location, and they no longer fit. Because they flower later in the season you want to prune them right after flowering should it be necessary. Otherwise, just a light trim will do.
If you’re growing them in a shrub border you can prune them by way of just deadheading the flowers. In some circumstances, you might want to leave the spent flowers so that the fruit develops for self-seeding or for the local birds to eat. If your plant is getting too big for its space, as mentioned, you can prune it in stages by cutting back the longer branches down to ground level but never removing more than a third of the plant at any one time.
Pruning the Mahonia x media
The Mahonia x media are more popular in landscapes because they are taller and wider specimens. They tend to grow in upright clumps and they have longer canes. They flower at the beginning of winter, usually in November and December. The flower heads will turn into seeds very quickly and fall off. If you don’t prune them, they can grow to be rather large in size, upwards of 2 metres to as tall as 4 metres once they are fully established.
If you have room to accommodate this size obviously you won’t need to prune to keep it in check, however, if you don’t have as much space, you should ideally be cutting one out of every three stems each year, at the beginning of spring as soon as it has finished flowering. You can cut it down to within 60cm of the ground.
With either Mahonia variety, it is important that you prune them as soon as they have finished flowering. This will allow the plant time to develop new shoots and to mature so that you get flowers the following season. And of course, make sure you give it a quick treatment of extra water and possibly fertiliser depending on the conditions after you have finished pruning. This becomes particularly important if you have pruned one third of the shrub.