Pruning Deciduous Bonsai in Spring. Between Leaf-burst and Midsummer

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Once a Deciduous bonsai has a full branch structure and foliage mass, it’s tempting to keep that perfect shape and repeatedly prune the entire tree from early Spring through until Autumn.
However, this repeated pruning and the lack of shoot extension can lead to a weaker tree, particular in the lower branches. For a tree to be fully responsive to midsummer defoliation and the resulting finer growth through late summer, it is a good idea for it to be allowed to extend a little, produce more adventitious leaves that will then pump up the strength of the tree overall.

acer palmatum japanese maple pruning

My Acer palmatum/Japanese Maple bonsai in May, 4 weeks after leafburst. I have kept the new growth in the crown tightly pruned but the lowest branches are being allowed to grow freely until midsummer.

My preferred method is to prune the strong apical areas of the canopy tightly, from leaf-burst onwards. This ensures that the crown remains finely ramified and not coarse. It also ensures that the naturally weaker lower branches are not suppressed by auxins in the crown.
The lowest branches are allowed to keep extending until the tree slows down and pauses growth at midsummer. It does lead to something of an untidy appearance for 4-6 weeks, but the benefits are worthwhile.

Elm bonsai pruning

My large Ulmus minor/English Elm bonsai, after the crown has been tightly pruned in May,3 weeks after leaf-burst. The remainder of the branches will be pruned at midsummer and then tightly pruned for the remainder of the season to create a huge number of ramified, fine shoots.

At midsummer, around the middle of June when deciduous growth pauses, I then prune back all growth to the framework established in the winter.That is, all shoots are pruned back to just one or two new internodes from the current growing season.
Trees are then defoliated, fully or partially depending on the tree, and the response is very strong. From midsummer onwards, all new shoots are repeatedly pruned as they appear anywhere on the tree, resulting in very fine and abundant growth. As well as invigorating the tree, this pruning technique also encourages thickening of the lower branches at a greater rate than in the crown. The additional top (foliage) growth also encourages stronger root growth that aids develop of the root system and nebari.