Cutting back Acers

Not sure I understand - where is the "top growth" you are referring to? That picture is of an acer (possibly a Shirasawanum cultivar) which seems pretty "bushy" to me. Looks like the upright growth was pruned back not too long ago.

Anyway, FWIW, you can prune acers pretty hard when they're dormant, usually between November and February. If you prune them while they're in growth, they can "bleed" a bit. I have a big Acer palmatum cultivar (4 x 4 metres) which I prune back now and again. In fact I've just pruned back a couple of branches by about a metre as they were getting in the way. It didn't seem to do any damage.

Thanks for the reply Jeff. Yes as you observed I have already pruned back a lot of the top growth to where I know from experience was safe to do so. At the back I am left with a number of bare branches about 1.2m tall which if left will simply bud and leaf at the top again. At the front again some branches about the same height but as you can see did leaf lower down if a little sparse. I want to try to get some leaf lower down. So the question is how far down can I cut the branches without killing off the shrub.

Richard

Prune lightly after leaves have dropped (aren't they nice and red right now ?) and don't remove too much, Avoid removing more than 20-30% of the crown. More on the RHS website

I doubt you will kill the plant as it is possible to pollard acers. However, one thing you could try is to stimulate the dormant buds lower down into growth by making a small slit in the bark a few mm above them. This cuts off the supply of an inhibitor hormone from above to the bud, and the bud will then start to grow as the plant will "think" that the shoot above the bud has been lost, and so needs to be replaced. If you want more info, Google something like: make dormant bud sprout

The OP could also post in uk.rec.gardening. It's quiet, but not entirely defunct