Stunted growth of Maples (plenty of leaves but no elongation of new growth)

Asked June 4, 2015, 10:39 PM EDT

I have a large japanese maple grown in a pot as a bonsai. The last two springs the tree begins budding as normal but as the buds/branching should begin extending it seems to stop and become stunted! It has plenty of leaves, but they seem to bunch in clumps!! What to do?? This also happened with two other maple bonsai I have (a trident maple and a small japanese maple grove). I have included photos of the larger tree as it exists today (one of the overall tree and another closer view of the leaf clumps) and one in healthier times. The photos are dated to help distinguish which is which. Can you help determine what I have or should do? Thank you, Ron Cascisa

Multnomah County Oregon

2 Responses

Undersized and tightly clustered leaves on a Japanese Maple in container may indicate need for repotting and/or root pruning.

Your current photos do not show leaf damage or discoloration; the problem is virtually certain to be due to an environmental condition, rather than to a disease or insect pest.

Your current photos do not show the plant's pot, but your photo from 2012 shows the same tree in a container in which it seems to be extremely crowded. True bonsai care always includes root pruning as one strategy to maintain a tiny plant size; otherwise, what you really have is simply container gardening... For a bonsai maple of this size, you would ordinarily be looking at root pruning about every two years. If it is actually growing instead as a container plant, it would need repotting into a larger container about every two or three years. If this plant has seen neither for longer than that, the over-crowding is very likely to be the cause of the situation you describe.

Interestingly, for many bonsai practitioners, the bunching of the leaves and reduced leaf size is considered a desirable condition, as it provides leaves on a small plant that are more in scale than larger leaves would be--and this effect is generally reached only when the young bonsai plant matures into it's final pot size. For true bonsai, the game is to maintain plant health and form once it reaches it's final size, by providing appropriate care, including regular crown and root pruning.

In your case, the sudden change might have a simpler explanation: your photos show the plant growing outside. If over time feeder roots had grown through the drain hole in the pot into the soil below, and you moved the pot, or even rocked it, with the result of breaking that connection to the ground, your tree would now be completely reliant on the limited resources within the pot, whereas formerly it could access resources from the soil below....

Two resources for additional information: Vertrees and Gregory, "Japanese Maples: the complete guide to selection and cultivation. 4th edition." This is available from many libraries. And consider tapping the local experience of many local bonsai hobbyists through the Bonsai Society of Portland, website

Thank you Justin. I plan on repotting and possible root examination/pruning in early spring 2016. I also will be soliciting the help of local bonsai professional Mike Hagedorn when I do. Thanks for your insights. I'm actually relieved it isn't more serious.