By Somhairle
Renfrewshire,
Scotland 
Advice needed on pruning my acer.
I have an acer palmatum and it needs a good trim. It is around 12 years old now, I think, and other that pruning away weak end shoots, I have done no pruning to the plant. However, it is now beginning to obscure the view from the house to the garden and is also very bushy.
I have checked online for some advice and it does say that they can be pruned in summer when it is good to be able to see the shape and fullness of the plant. However, I am looking for some tips on what I can do with this acer.
Is it possible to use hedge trimmers on this as it would certainly make shaping the outline much easier? I understand that it is not too wise to reduce the height as it will simply encourage the plant to produce long spindly growth. However, in the photos you can see a spur on one side and wondered if I could reduce this in length to make the shape more 'symmetrical'? And........ should I try to remove some branches throughout the shrub to give it more of a tree like shape and make it much less dense?
8 Jul, 2019
Answers
Thanks, Bathgate. I thought that it was ok to prune just now, but I'll take your advice. So, I'll file this away until later in the year and return to it then. :)
9 Jul, 2019
Your tree is absolutely beautiful. It's very vibrant & healthy looking. I have an acer as well (Acer Rubrum).
Not now! If it's not an absolute dire emergency, wait until the tree goes dormant. Now is the worst time to prune. Pruning now while the sap is flowing will open the tree up to pathogens like ringing the dinner bell. Acers are notorious bleeders. They bleed for days losing precious sugars.
In the fall/winter, your pruning job will be 100x easier as you can visually see the tree structure, mark with a piece of chalk which branches will be cut. The tree won't bleed as much and no pathogens around to infect.
No flush cuts! Be careful not to cut the branch collar - the slightly raised collar that adjoins the branch to the main stem. Don't cut that collar. That's from where the tree heals over.
No dressings! Don't paint or dress the cuts in anyway at all. They do more harm than good. Let the tree heal over naturally. The cold weather will keep the wound sterile while the tree heals over.
1/3 Don't cut more than one third of the canopy. You don't need to pull out your scientific calculator. Just do it visually.
Tools you'll need. Eye protection, garden gloves, bypass hand pruners, lopers, pruning saw - for limbs over 3 inches in diameter. I doubt you'll need the saw, but if the lopers won't make a clean cut, use the saw.
Here is a short video that shows how glorious these trees become as they mature.
Best Trees for Small Garden Spaceshttps://www.youtube.com/watch?v=o5whJ6R-UZ8&t=29s&app=desktop
8 Jul, 2019