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Botanical Name – Acer palmatum
Botanical Name – Acer palmatum
Common Name – Japanese maple
Native to – China, Korea and Japan
Botanical Information – First described in the west by Thunberg in 1784. A small tree to 30 feet high and can be twice as wide. Leaves are 5-7 lobed with doubly serrated edges. The botanical history of this tree and its related species is long and confused. The best sources for detailed information on the history and construction of the family can be found in J. D. Vertrees excellent book on Japanese Maples (ISBN 0-917304-09-8) or “Maples of the world” by D.M. van Gelderen, P.C. de Jong and H.J. Osterdoom (ISBN: 0-88192-0000-2).
General – The Japanese maple has been in formal cultivation in Japan since the 17th and 18th centuries. For bonsai, it makes sense that its use has also been long and fruitful. Over the years there have been many hundreds of cultivars, with many still in cultivation and many more that have probably been lost. From a care perspective, treatment of the cultivars is the same as the species with the exception of pruning. The dwarf forms requiring little to no pruning (other than design considerations) at all because of their short internodes. The bark of the species when young is bright green and turns to a beautiful grey with age. The cultivars may vary from the normal green bark when young to brilliant red, as is the case with Sango KuKu, or dark purple with those in the Blood Good (ssp: amoenum) group. However, they will all turn the typical grey with age. Leaf size will also differ between the subspecies (a smaller leaf) for the palmatum group (ssp: palmatum) and the Blood Good group (usually larger by half) which will have an impact on the size of the bonsai to keep it in perspective. Because of the number of variables in this species, it is an excellent choice for bonsai and will provide the enthusiast much to consider in selection and use.
Cultivars – Too many to list. Refer to any of the excellent reference books on the subject.
Japanese maples like a light shade to keep the leaves looking fresh during the growing season. Full morning sun with light shade during the heat of the day is just what the doctor ordered for this tree. The leaves of this tree are thin and delicate and will often burn in the hot sun, particularly when a plant that has been in the shade is moved to direct sun. An over exposure to the sun can scorch the leaf like a sunburn or cause the edges of the leaves to dry, turn brown, and shrivel, but will not harm the health of the tree. For those in the Southwest of the US, where the environment is rather warm and dry, a light shade should be provided all summer long.
The Japanese maple is fairly winter hardy and will grow in the ground to Zone 5 (refer to the U.S. Agriculture hardiness map). For bonsai or plants in containers, they should be provided winter protection in Zones 7 and below. Winter protection can be as simple as covering the container with pine needles, or putting them into a simple cold frame or an unheated garage.
Japanese maples like to be kept evenly moist at all times. Water quality is an issue with this plant. They seem to dislike hard water with dissolved salts and an excessive amount of chlorine. Many who have grown this tree, myself included, believe that these salts and chlorine are some of the culprits responsible for summer leaf burn. If you don’t have many trees and have access to collected rain water, it does the best job. In lieu of that, using tap water that has been allowed to stand for at least 24 hours is a good alternative. Occasional flushing of the soil is advised. It is also not recommended to spray the leaves with anything other than rain water. It has been my experience that trees whose soil contains a clay component seem to inhibit leave burn better than those that do not.
Japanese maples, as is the case with most maples, love food when they first come out in the spring. It is this fact that one should keep in mind when developing a fertilizing program. Most maples when they first bud out in the spring want to grow vigorously if they have adequate amounts of nitrogen. For the finished bonsai, where you’re attempting to keep the growth small and diminutive, you should use a low nitrogen fertilizer until the growth stops sometime in Mid June. After Mid June a regular multi-purpose fertilizer can be used until the end of the growing season.
For the finished bonsai, pruning is done during the late spring, once the growth stops in mid summer, and then again if necessary in the fall. The spring and summer pruning is actually more pinching than pruning. It is done to keep the tree in check and encourage branch ramification. Let the summer growth go until it has 3 to 4 sets of internodes and then cut back to the first set of leaves. I don’t recommend pruning any major branches during the early spring at all. Japanese maples will bleed profusely, and large cuts could severely damage or even kill a tree. All major pruning should be done in the fall, before the trees are put away for the winter. Most beginners don’t prune or pinch this tree enough. Have no fear in pruning, this tree it has dormant buds that will sprout from almost anywhere that a branch is cut and often everywhere, even on old wood, when a severe pruning is done. Wound healing is rather slow with this tree.
Wiring Japanese maple should be done just as the tree loses its leaves in the fall. It is in this period of the season that the branches are still pliable. With the onset of winter, the tree expels water from the branches, making them brittle and subject to breakage. In addition, Japanese maple bark is very thin and can be easily damaged, so take care while you’re wiring. 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. Japanese Maples put on most of their trunk and branch diameter in the late spring after new growth has matured and in 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 very closely. Once a branch is girdled, it can take years for the girdling to disappear, if ever.
For young trees, repotting and root pruning should be done every 1 or 2 years. For older established trees, it can be as long as every 3. No matter how old the tree is, the roots should be inspected every spring before the buds swell. This will allow one to evaluate not only whether the tree should be repotted, but more importantly the health of the roots. Timing should coincide with the onset of root growth, which is long before the buds swell in the spring. Look for the tips of the roots to be white and actively growing, and that will be your signal to get on with the job of root pruning.
Propagation of the species is by seed. The cultivars are either grafted or cutting grown.
Seed - stratify for 90 days at 38 degrees F prior to planting.
Grafting – Root stock should be brought into the greenhouse in early February and grown until it leafs out. Once the root stock is growing, scions should be collected from dormant plants and grafting can take place. Most common method is a side veneer graft. Summer approach grafting may also be done.
Cuttings - Summer cuttings will give the best results but will vary between cultivars. The dwarf cultivars are rather hard to get to root.
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.
Japanese Maples are extremely sensitive to verticillium wilt for which there is no control other than cutting out the affected branches well below the affected area to healthy green wood. It is also important to remember to sterilize your tools between cuts. 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, which is registered for use against anthracnose on maple and elm. 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.
|March 2004||March 2008||March 2010|