I have a star magnolia (Magnolia stellata) which has outgrown its space – it is about 10ft high and the same across. My RHS pruning book suggests that it should be pruned by removing whole stems back to the point where they branch out – should it be done now?
Wait until after flowering (around midsummer) and don’t go mad, because in my experience this produces a lot of dieback and many watershoots – long, straight, whip-like growth that’s a response to losing too much leaf.
Instead, aim to do a quarter each year until you’ve got it back to a reasonable height. Magnolias can be slow to recover. Reduce the overall height of the crown by thinning out each stem, reducing the height little by little rather than chopping the tree in half. If you want to reduce the height of a single branch, prune it back to where it naturally forks, rather than cutting it in half. With young growth you can tip back to a bud. But if you just hack at the height you want, you may end up with lots of stubby dieback. I know it’s annoying to think that it will take years, but a tree that is alive and healthy is far easier to look at than one that’s stressed.
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