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Botanical Name – Acer carpinifolium
Botanical Name – Acer carpinifolium
Common Name – Hornbeam Maple
Native to – Japan
Botanical Information – A deciduous tree to 30 feet densely branched and rather upright. The leaves are oblong 1 ½-2 inches wide and 4 to 5 inches long. Leaves are a rich green with doubly serrate edges and prominent leaf veins reminiscent of the Carpinus (Hornbeam) family. The leaves are very similar in appearance to the Japanese Hornbeam but just a tad bit larger and of a lighter green coloring. Leaves of Acer carpinifolium are placed opposite along the branches where the true Carpinus leaves are placed alternately along the branch. Fall coloration is often a brilliant yellow. First described by Siebold & Zuccarini in 1845.
General – This is a tree that at first glance you’d swear was not a maple. It is one of the very few maples that does not have any leaf lobes at all and has disguised itself in the clothes of a Hornbeam. I have never seen Hornbeam Maple as a bonsai but that’s not surprising knowing how hard to find it is in the United States. Some would even consider it on the rare side since it is really only found in the collections of arboretums or Maple enthusiasts. Despite its not being used much as a bonsai it has, in my mind, good possibilities and is worthy of evaluation. The branching structure of this tree and its ability, like most maples, to bud from old wood help it satisfy most of the criteria that a plant needs to make a good bonsai. This tree will trunk up in size rather quickly if given enough room while it’s young, even if you continually prune it to encourage lower branching. Since the internodes of this tree are a little large and the coarseness of the branches, a larger bonsai is recommended. However, with consistent pruning for reduction in internode length and some level of leaf pruning to encourage smaller leaves a good medium sized tree in the 18 inch range can be had.
Cultivars – Esvld Slelect - A dwarf fastigiate form developed in Boskoop Holand
This tree likes more sun than the other maples. If given too much shading it will become leggy and slender, making the job of branch ramification all that much more difficult. Full sun in the morning until noon is required and maybe some in the late afternoon if it can be given would not be a bad thing for the tree in a bonsai container.
This is a real winter storm trooper of a tree. It is good to Zone 3 when grown in the ground so most likely winter protection will only be necessary in Zones below 5. Because there is not much data on the root performance of this tree in bonsai culture it would be best to be conservative at first. Given the Zone 3 rating I would not hesitate to just provide the tree with a simple cold frame home for its winter hibernation. It should be noted that in Japan you can find this tree in mountain forests up to sub-alpine heights.
Hornbeam Maple needs adequate water at all times. The amount and frequency of your watering program will largely depend on the type of soil, daytime temperature and wind that your trees experience. The objective is to keep it evenly moist at all times. There is no simple rule!!!
Any good complete commercial fertilizer at the recommend strength and frequency during the growing season would be more than adequate. If you use a constant diluted fertilizer approach that would be just fine as well.
Summer pruning of this tree should be done on a regular basis to keep the growth in check and promote additional budding wherever possible. As is the case with all maples heavy or major structural pruning of large branches should only be done in the late winter 4-6 weeks prior to bud swelling.
Wiring Hornbeam maple should be done just as the tree looses its leaves in the fall. It is this period of the season that the branches are still pliable before the onset of winter when the tree expels water from the branches, making them brittle and subject to breakage. Wire can be maintained on the tree until it buds out in the spring. Of course you can wire this tree during the growing season but if you’re not careful it will girdle in a heartbeat. Hornbeam Maples put on most of their trunk and branch diameter in the spring and that short period at the end of summer before the trees take on their fall leaf color. It is these periods of the year that wiring is not recommended unless you watch your trees every day. Once a branch is girdled it can take years for the girdling to disappear, if ever.
Repotting of young trees should be done every other year as long as they are growing vigorously. Older trees in good health should only need it every 2 or 3 years. As always though, the roots of the tree should be looked at every year during repotting season. Repotting should be timed to coincide with the onset of root growth in the early spring prior to bud break.
Propagation is typically through seeds. It should be noted here that seed viability of this tree is often questionable. Trees are of separate sex (dioecious) and if the seed tree does not have a male tree in close proximity the seed will be sterile. Cuttings are also possible but difficult. Grafting of the cultivar has been recorded as being difficult.
Seed – Stratification for 90 days at 38 degrees prior to planting.
Cuttings – Summer cuttings are best.
Pests and Diseases
The types and number of pests and diseases will greatly depend upon your location and the spraying program that you have established for your trees. In general, the pests most commonly seen are Mites, Aphids, and Scale. Mites and Aphids can be controlled with commonly available insecticidal sprays using the recommended methods that come with the product. For those who don’t like to use insecticidal sprays these pests can be kept under reasonable control by using a strong spray of water late in the day just before dark. Aphids tend to locate themselves at the soft new growth. Mites tend to be on the underside of the leaves at the leaf veins. Scale can appear both during the summer and winter months and appear at branch junctions and are sometimes difficult to notice. The best recommendation that can be made is to develop a relationship with your local Department of Agriculture or Entomology agents to get familiar with the pests in your particular area.
The hornbeam maple seems to be somewhat more resistant to fungal diseases than the other maples but can still become infected. Hornbeam maples are subject to verticillium wilt for which there is no control other than cutting out the affected branches well below the affected area to healthy wood. It is also important to remember to sterilize your tools between cuts too. The most effective control for verticillium wilt is the control of the soil you use as it is where the verticillium spores live. Taking measures to sterilize your soil or ensure that it does not become infected will go a long way to help make sure you are not plagued with this devastating disease.
Anthracnose can be effectively controlled with a chemical mixture of hydrated lime, copper sulfate, and water, known as Bordeaux mixture. Anthracnose is encouraged by wet spring weather as the tree begins to leaf out. Using the spray prior to bud swell is advised as well as good air circulation in your growing area. As is the case with all dormant trees it is wise to always apply a dormant spray before you put the trees away for the winter and then again just before the buds begin to swell in the spring.