Japanese Maples for Bonsai

by Brent Walston

Introduction

Recently on the internet I was asked what is the best Japanese Maple, Acer palmatum, cultivar for bonsai? This is a really tough one to answer. The short answer is that they are all good candidates, choose what you like. The more complete answer is that there are specific cultivars more appropriate for the size and style of bonsai you desire.

I will avoid for the most part specific cultivars since the list runs into the hundreds but rather talk about the types or groups as they apply to bonsai. You should use Vertree's book Japanese Maples for descriptions and culture of the many cultivars.

Choose a Cultivar Appropriate for the Size of Your Bonsai

Nearly all (if not all) Acer palmatum exhibit juvenile and adult characteristics. In landscape trees the adult characteristics of small leaves and close internodes seems to occur at 20 to 40 years, but this will vary by cultivar and environment. Under bonsai conditions, plants may begin to attain these characteristics in as little as five years or less. One should plan the bonsai based on mature leaf and internode size.

I don't think there is a single bad cultivar or seedling type for bonsai. The trick is to pick the suitable ones for your design. The larger leaf, more aggressive ones are suitable for larger two to four foot bonsai. For this size, a four inch or larger trunk would be best for most styles. This involves growing the tree in the ground or container to get the trunk size needed first. One or two trunk chops will be necessary to get the taper and apex. It will take ten to twenty years to get to this stage. From the finished trunk it will take another five years to get good ramified branches. I hope no one is put off by this time line, you can grow other trees at the same time so you have something to play with in the interim. At fifty I am still starting projects like this.

Types for Small Bonsai

There are many small leaf, short internode types that make good smaller bonsai, from mame to shohin and larger. These 'Yatsubusa' types have different characteristics, some are painfully slow, others are actually quite aggressive even though they are small in stature. The dwarf cultivars really should be grown from cuttings for bonsai or grafted very low. Even the low grafts may present problems down the road. Cutting grown ones will give you a very nice thick radial root pattern that will swell into a broad crown and excellent nebari. The uneven growth rate between the scion and the understock in dwarfs will give a necked down appearance in grafted plants after a few years. This problem gets worse, not better with age. A very low grafted plant minimizes this problem.

Dissectum Types for Bonsai

The highly prized dissectums present the biggest challenge for bonsai in my opinion. Not many of these can be grown from cuttings, and must be grafted. Since most of these are cascading or weeping habit trees, many plants are grafted high, or onto standards for landscape use. Very few nurseries are grafting low for bonsai. Mountain Maples is one, Del's is another. Understock/scion matching is also very important here. The slower cultivars should be grafted to small leaf, small seed understock, and there should be some attempt to match bark color for bonsai.

Rough Bark Types for Bonsai

The textured bark cultivars must be cutting grown for bonsai use. Unless a plant is low grafted and the graft union is BURIED (risky business with this species), or air layered there will be a distinct line at the graft union marking the smooth understock and the beginning of the corky scion. Cutting grown plants will even exhibit corky surface roots as well as trunks. Fortunately, the rough bark cultivars all seem to be quite easy to grow from cuttings and several are readily available. Most of these cultivars will not begin to show the bark characteristics until about five years, and good corking will not be apparent all along the trunk until about ten years. These trees will fall into an intermediate category of medium to large size bonsai with a time line of ten to twenty years for a decent tree.

Seedling Types for Bonsai

There is nothing wrong with using seedlings for bonsai culture, in fact most of the spectacular maples one is likely to encounter as bonsai are seedlings. It is very difficult to trunk chop a ten year old cultivar, most people just can't bring themselves to do it. There is a seedling type which I call small leaf, small seed. These seedlings will reach maturity faster and will have adult leaves and seeds about half the size of other green seedlings. These are superior seedlings for bonsai, although the difference won't be apparent for five to ten years, even as bonsai. Green seedling leaves can eventually be reduced to less than an inch and can even be trained for mame.

Red seedlings, Acer palmatum atropurpureum also will make good bonsai and are an inexpensive source of material for the spectacular spring red or purple foliage. These don't reduce as well as the green seedlings and are more suitable to medium to large bonsai. I think two to three inch trunks would be an acceptable starting point for these. This means growing out nursery plants in five gallon, then fifteen gallon cans to get the caliper. This takes about five to eight years. Of course one can always purchase fifteen gallon nursery stock and cut it down, just don't let anyone watch or they will call the cops.

Most field grown or untrained A. palmatum seedlings, red or green, are worthless for small bonsai because of the internode length. This will not matter much for larger specimen, but it is critical for mame and shohin. Unrestricted seedlings make internodes about an inch or less for the first year, or for about the first three to six internodes. After this time they become established and have the resources for stronger growth. At the late part of the first season or the middle of the next season the internode length will increase dramatically as the plant explodes into aggressive growth. The internode length may jump to six inches or more. For a small tree this will give a REVERSE spacing of ascending branches, with the largest spaces at the top of the tree. This is not easily corrected.

Budbreak on Old Wood

It is true that A. palmatum will sometimes sprout from adventitious buds (dormant buds between the internodes), but it has a very strong predisposition to bud out only at the nodes. After a trunk chop they may even produce a whorl of branches from dormant buds, but only at the nodal points. These nodes are clearly visible as bands on young trees that have not as yet attained mature bark. So if you are evaluating seedling or other stock for small size bonsai look for this internodal spacing and plan on having branches only there, or trunk chopping out these long internode sections and growing a new trunk line.

I select out the vigorous seedlings that have large low internodes and use them for larger stock where the lowest branch will be at least six inches high. I also keep seedlings in small pots pruned down until the roots colonize the pots and slow down the growth before selecting a new trunk line. This also has the additional benefit of adding nice soft curves to the lower portion of the trunk.

Seedlings for Group Plantings

Green seedlings make excellent material for group and forest plantings. The same precautions about internode length apply. Indeed, it is even more important for this style since the trees will remain small.

And finally

So, you can see that the question is not so much, what is the best cultivar, as what is the best cultivar or seedling type for what you want to achieve.

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