Question about Japanese maple pruning frequency

[guimeixen]

I have a question regarding the pruning of a dwarf Japanese maple I have which was sold as Little Princess. I am in northern Portugal, so the plants starting growing earlier than in a lot of other colder zones, and from what I've read this variety begins to grow quite early. This spring I let it grow freely until it stopped and then I pruned it back. Now it has a lot of new shoots again which have grown a bit, and it's starting to become a bit congested and shading out more interior branches. Would you prune it again?
If yes, it would probably grow again, as it's only the beginning of June. Would you keep pruning it during the growing season if it grew again, except if we start getting towards late summer?
Also, how much should I let the branches extend, keeping in mind that I want to keep the shape it has and I'm not interested in thickening the trunk more?

One more thing, these new leaves are a lot larger than the typical ones of this dwarf cultivar, is this normal? Happened the same thing after I pruned last year, the new shoots produced leaves quite a bit larger.
In the images you can see the new shoots and in the second image you can see where I circled the green leaves that grew in the beginning of spring compared to the larger ones growing now.

 

[Shibui]

I trim Japanese maples as often as they require it. That often depends what stage the tree is in. For developing trees where I want increase in trunk thickness or thicker branches I allow shoots to grow - sometimes a full season to add lots of thickness, other times let them grow to 4-6 pairs of leaves then cut when developing more ramification.
No picture of the entire tree so hard to guess where it is in development stages.
Trees that have achieved good branches with plenty of small twigs I only allow shoots to extend 1 or 2 pairs of leaves before pinching out tips. Sometimes do that every few weeks right through growing season. There's no limit to how many times. Longer growing season will mean more growing and therefore more trimming.

Larger leaves are common if maples are growing well. Just keep cutting the shoots back. Also check where those shoots are coming from. It is common for JM to shoot new buds from the trunk. Those shoots often grow strong and if allowed to stay will cause local thickening on the trunk or branch. Need to be chopped as close to the trunk/branch as possible if they are not a vital part of the design.
Small leaves are often weaker shoots. Not sure why some are strong and grow long while others don't extend and have smaller leaves.
Maybe ease up on fertilizer next spring to try to slow growth a bit more unless you are still building branches or ramification.

 

[Brian Van Fleet]

If the tree is in that final stage of development where the goal is to increase the twigginess, then you’ll want to pinch out the center bud as they’re just emerging in the spring. This usually halts the growth to one pair of leaves on a short internode.

Based on the photos and your description, you may consider a partial defoliation, pruning back all shoots to a single pair of leaves, then removing one leaf out of each pair. This will allow light into the tree and strengthen interior buds.

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[guimeixen]

Thank you for your answers!