Last November I pruned a lot of branches of a acer tree that was getting too tall, as it is close to the house. This summer, very many shoots grew form just below each cut branch. These new shoots grew about 36 inches long, from April to August, which surprised me. Now this November I have had to go up and cut off off these new shoots to stop the tree getting bigger again. How can I prevent thyis fast growth of so many new shoots, sometimes three from each cut?

Hi royroy, Pruning any plant when its dormant generally encourages growth, as the subsequent growth has all season to grow, thus becoming large. Having pruned these new growths again now, all that will happen will be a repeat performance of last year, so you need to break this cycle ! To do this, you prune about mid August, this gives the subsequent growth enough time to sprout but not enough time to grow large before the end of the season. So basically, summer pruning will have a more dwarfing effect, this of course is the principal behind the summer pruning of fan trained and dwarf apple trees.
hope this helps, Lannerman.

Than you! I will try again next year.

The basic points to know about pruning trees to affect their height / bushiness are that if you take some off the top it will encourage it to bush out, (crown lowering) and if you prune off lower branches, it will encourage it to grow taller (crown lifting). As for time of year, I don't think that's critical with an acer.

You can't necessarily prevent multiple new shoots forming, but you can thin them out, which is easy when they are only just formed. 3 from a cut, incidentally, is hardly "many", indeed I would go so far as to call it "few". You should see the spiders that grow out from the pruning cuts on my neighbour's Norway maple. Or from a pruned hawthorn.