Pruning an Oregon Grape (Mahonia aquifolium)

I have a large, mature oregon grape (about 3.5' high x 9' wide). I want to plant a small bare-root plum tree (currently about 4.5' tall) towards the middle of it. To give the plum tree an advantage, I'm thinking about cutting the oregon grape to about 2' so it won't shade the plum tree. I would like the oregon grape to grow back to its full height once the plum tree is established. I know some broadleaf evergreens do fine with heavy pruning and others never grow back. I've been unable to find much information about pruning this species other then "prune following bloom". Any advice would be greatly appreciated.

Brown's Pruning Trees, Shrubs, and Conifers says that M. aquifolium can have it's upright growth and suckers pruned in April down to 100-200 mm (a few inches) and that it can be done at intervals over a few years or annually.

Much as I enjoy Guy S's rapid response to all my pruning questions, I should know this stuff myself. Therefore I'm going to ask you all for suggestions on the "be all, end all" pruning text. I took Mick's response to Amazon and although professional reviewers lauded Brown's work, the only non-professional comment thought it next to worthless. I'd like to buy the best reference possible. Comments? Ken

Willmetge:

I'm obviously not from the Pacific Northwest gardening region, but have had the opportunity to have gardened around a patch of Mahonia at my parents' house that is at least 40 years old. My comments are based on this experience.

Assuming that the species you have is Mahonia aquifolium, and that the 3.5' x 9' size refers to a colony of multiple stems, I'd say you should prune the center down to 6" or so only in the area you need in order to plant the new plum. Then, observe how the Mahonia reacts to this reduction while the plum is getting established.

Take this knowledge and apply it to the rest of your colony as you see fit: occasional reduction in order for the plum to thrive; rejuvenation if the colony loses vigor on older stems; or balancing vigorous stems vs. weaker growth if you want some uniformity across the mass.

Expect that the Mahonia will have more vigor in sunnier and less competitive zones, and grow less vigorously where denser shade and more competition occurs, as I suppose will be the case once your plum takes hold.

If you have a different Mahonia than M. aquifolium, disregard all my statements. They are probably not applicable to the other species, with which I have little familiarity.

I want in the worst way to respond to our esteemed poster from northern WI, but I don't want to hijack the Mahonia thread. I'll go off off-thread.

I'd prune it to just the height you need, just above the leaf node. It will send up a new "leader" later. I'd also recommend, seeing you're already there, to top-dress it with a bit of organic & peat mix and throw in a bit of slow-release fertilizer. With a bit more moisture in summer they look greener and fresh.

The book I use is "Pruning" by Christopher Brickell. Simple, line drawings, genus specific.