Harry HarringtonArtist and Author, Bonsai4me · Author, Publisher, Webmaster, Bonsai Artist

Partial Defoliation of Japanese Maple Bonsai

18 Jun 2022 · 3 min

Watch on YouTube

3:26

In this instructional video, bonsai enthusiast Harry Harrington explains how and why to perform partial defoliation on a Japanese maple (Acer palmatum) grown in the UK. He begins by noting the favorable spring growth and midsummer timing, emphasizing the need to consider local climate (max ~30 °C) and the risk of leaf burn on trees with weak root systems. The primary goal of the technique is to protect existing ramification by improving light penetration and airflow within a dense foliage mass, rather than to dramatically increase ramification, though modest new shoot growth may occur. Harrington describes a straightforward method for trees with opposite leaf arrangement: remove one leaf from each pair while leaving the petiole, but retain both leaves in weak or interior areas to maintain vigor. He demonstrates the gradual removal across the crown, resulting in a lighter, more airy canopy that still retains many leaves. He also references a different approach for species with alternate leaves (hornbeam, beech, oak). After defoliation, he stresses the importance of feeding and watering the tree to ensure vigor before returning it to its garden position.

Chapters

We've had a wonderful spring here in the UK this year, and growth on my deciduous trees has been particularly good. Now that it's midsummer, it's time to start pruning my bonsai and defoliating those trees that would benefit from removal of some or all of the leaves. This Acer palmatum, or Japanese maple, is a tree I started in 2004. And its journey with me has been featured in a couple of my previous videos. As can be seen here, the ramification of the foliage mass has become very dense over the years, with a huge number of leaves. The tree is positioned in full sun in the garden. This makes sure that plenty of light gets to all of the leaves and helps reduce the size of each individual leaf. The danger can be leaf burn. A Japanese maple with a weak or poorly functioning root ball will start to burn if it is unable to supply enough moisture to the foliage mass from the roots. Bear in mind here that the maximum temperatures in the UK rarely reach over 30 degrees centigrade. If you're in any doubt, give your Japanese maples partial shade. Today I will be partially defoliating this tree, not to increase ramification particularly, but to protect the ramification that has already been achieved. Ensuring that light can penetrate the foliage mass reduces the possibility of the loss of shaded branches in the interior. This technique can be carried out on all deciduous trees that put out leaves in pairs, and are in the same late stages of refinement. If there isn't enough light or airflow reaching the interior, the branches there will start to die off. For deciduous trees that have alternate leaves, such as hornbeam, beech, and oak, I have a different method of partial defoliation, and that can be seen here in this video. The method for partial defoliation on this acer is straightforward. One of each pair of leaves is removed, leaving the petiole or leaf stalk behind. In areas of the tree that are weak or in the interior of the branches, leave both leaves in place to ensure their vigor. Here you can see where I have slowly worked my way across the crown of the tree, reducing the number of leaves by half. With work completed, it is possible to see that although the tree is still endowed with a great many leaves, there is much more light and airy feel to the foliage mass, allowing the interior to be exposed to the sunlight. Although it isn't the main reason for this partial defoliation, there will still be an increase in ramification, with new shoots emerging from many of the places where a single leaf has been removed. After defoliation, I ensure that the tree is well fed and watered for maximum vigour, and then it's returned to its place in the garden.