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Botanical Name – Acer campestre
Botanical Name – Acer campestre
Common Name – Hedge Maple, Field Maple
Native to – Europe and Western Asia
Botanical Information – First described by Carl Linnaeus in the mid 18th century. As a tree grown in the open ground, it is a round crowned tree that will reach 30-60 feet high but is also found quite often as a low wide shrub. Leaves are 3-5 lobed smooth along the edges and of a light green coloration when they first emerge in the spring, and subsequently turning a darker green as the leaves mature. The leaves can be as much as 5 inches across but usually much smaller. Bark is a corky light brown or tan coloration with stiff branches. Flowers are borne in terminal clusters and the typical light green coloration so common to the Acer genus. Fall coloration is usually a light yellow. The species name comes from the Latin “campestris” meaning “from the field”.
General – Acer campestre is seen more often these days as bonsai in those areas where it will successfully grow in the United States. In the United States, it is fairly difficult to find in the retail nursery industry but will often be found at the larger bonsai shows, where there are a sufficient number of vendors. From a single tree design standpoint, it is used most extensively as an informal upright but works very well as root-over-rock, natural, exposed root and even the raft style. Very rarely if ever seen in multi-tree groups or forest configurations but would be worthwhile attempting them, even though they might be difficult because of the idiosyncrasies of the tree’s growth habit.
In my humble opinion, the most interesting aspects of this tree are the rough furrowed bark, the shape of the leaves and the large dark (almost black) dormant buds. It is a fast grower and will bulk up in size quite quickly when grown in the ground or even in a container. Branches are fairly large in diameter even when they are young, and if the growth is not controlled the internodes will be long, causing some difficulties with ramification. The roots of this tree, when exposed to light and air, take on the rough bark characteristics of the trunk, which is why it is so often seen in the root-over-rock design. It is not uncommon to see growth sprout from the exposed roots which can be advantageous to some designs but if not needed should be removed as it appears.
Cultivars – More than 35 cultivars have been identified but are rarely, if ever, seen in the United States. Some of the cultivars that might be fun to attempt, if you can find them, are:
- Compactum Nanum
- Green Weeping
- Red Shine
- Royal Ruby
Acer campestre in its native environment will often be found as an understory tree and will tolerate a good amount of shade. As a bonsai, however, too much shade will encourage larger leaves and make for a tree out of scale particularly if you’re trying to grow a smaller bonsai under 12 inches or so. Direct morning sun, with some light protection during the hottest part of the day during the summer months, will do the best for this tree. In the late summer and early fall, when the temperatures begin to subside, direct sun all day will help in some years to produce better fall coloration. Poor sunlight at this time of the year will often just produce brown leaves.
Rated as a US horticultural Zone 4, Acer campestre is hardy to -20 degrees F when grown in the open ground. As a container plant, it should be given winter protection in Zones 6 and lower. Most of the temperate deciduous trees will not perform well in sub-tropical or tropical environments, due to the lack of satisfying winter chilling requirements
As is the case with most maples, Acer campestre needs constant moisture during the active growing season. Containerized trees are difficult to over water when the soil is in good condition. More often than not, trees that die in containers from what is thought to be over watering are usually the victims of the organic matter in the soil breaking down and becoming too fine of a particle, inhibiting drainage and encouraging root rot. Trees that have become damaged from a lack of water, if caught in time, can be resurrected if put in light shade and watered immediately by watering the soil 2 or 3 times to ensure that it is thoroughly wet and spraying the dried leaves and branches of the tree. In 3 weeks or so, the dried leaves will drop off, and a new set of leaves will appear.
Any general purpose “complete” fertilizer applied during the growing season will be more than adequate. Acer campestre in its native habitat grows on “neutral” to slightly “alkaline” soil, so an occasional application of lime to keep the soil at the right ph will help keep your tree in good condition. Remember to never fertilize a tree when the soil is completely dry or when it is sick.
A successful Acer campestre bonsai is often due to the attention given to pruning. The level and kind of pruning will greatly depend on whether the tree is “in training” or if it is a finished bonsai. Trees in training, which are allowed to grow more freely, will produce vigorous growth that has thick branches and long internodes. Keeping this growth in check by diligent pruning will greatly enhance the speed with which you are able to make a tree with good structure and appearance. Strong terminal growth is often set with 5 buds (1 terminal bud and 4 lateral buds) which should only be allowed on the main branch that will form the trunk and apex of the tree, and in the case of “natural” designed trees on the main side branches. Side branches which will form the canopy of the tree should have this type of growth removed. Bud placement on the branches is alternating, meaning that the first set of buds will be in the horizontal position and the second set will be in the vertical position. You can use this to your advantage if you plan appropriately when doing your pruning. Tightly pruned trees will form dormant buds almost everywhere, so don’t be afraid to prune a tree back more so than you might with other species.
Wiring can be done at any time of the year, but due to this trees fast growth habit, it is best to wait until late fall just as the tree is shedding its summer leaves. Due to the nature of the stiff branches that gain girth quickly, it is important to wire branches when they are pliable, as once they harden off you will find that they can break quite easily. A good plan is to prune this tree with wiring in mind. Wire should be removed as the buds begin to show color in the early spring.
Repotting should be done every 2 to 3 years on established bonsai. On quick growing trees, however, it is wise to check them every year. A good mix for this maple (and most maples in general) is 40% structural material, 30% organic material and 30% clay.
This species is typically grown from seed, and the cultivars are more often than not propagated from either cuttings or grafted. Seed should be gathered in the fall and planted immediately or stratified for 90 days at refrigerator temperatures then sown. Seed allowed to dry out will not germinate until the second year. Cuttings taken in the summer months when the wood is “half-hard” will root, but if timing is not perfect the percentage of cuttings that take will very from good to poor.
Pests and Diseases
No significant problems exist with this tree other than the typical aphids, mites, scale and borers. A properly formulated spraying program will be more than adequate for this tree. A good summer spraying when insects are noticed will go a long way to protect the tree. Dormant spraying should be done on this tree as scale will overwinter on the branches and may go un-noticed by the novice.