You can hard prune Mahonia, so if yours is fairly large and a bit tired looking due to age or the severe winter, then you can start again by cutting all the main trunks down to aprox 3ft to the ground, by doing so new buds will break and shoots will soon follow, have carried this excercise out many times and they always respond well, give it a good watering and as a rule i do mahonias early may so all the new growth has the rest of the season to ripen/harden off, julien.

Thankyou Julien I shall take a photo tomorrow and post.

I have a mahonia about the same age. Every few years it gets a haircut (cut just above a leaf joint about this time of year) and a feed it is still happy and healthy