Korean Hornbeam Bonsai Care Guide
Carpinus sp. is a family of approximately 41 deciduous trees native to temperate regions of Europe, North America, and – predominantly – Asia. Carpinus coreana is, as the name implies, native to Korea. Although Korea did export many of these trees in the last couple decades, it is difficult to obtain an imported specimen now as they are trying to protect the native population. It may grow to 50 feet in its natural habitat, and produces a very hard wood that in ancient times was used in building ships, and in fact is nicknamed "ironwood".
This cultivar is prized for its small leaves – which may grow up to 2" in length and can be reduced to less than an inch – as well its fascinating pleated foliage and stunning fall color show. The leaves may turn yellows, oranges, or reds, and sometimes will even turn two different colors on either side of the vein on the same leaf. In spring the tree produces seed pods with a hop-like appearance and small white catkins. The bark is grayish, smooth but fluted with a muscular look.
Carpinus requires protection from freezing temperatures in winter and full afternoon sun in summer. It does however, appreciate a dormancy period in a cool place, with root insulation. An unheated garage or cold frame works well for this purpose. While this tree will flourish in partial shade, the more sun it receives means the denser the foliage will become.
Korean Hornbeam should not be kept as a full-time indoor bonsai – it may be brought inside for short periods to be displayed but should spend the majority of its time outside.
This species does well with moderate watering. It should not be allowed to dry out completely but can tolerate mild neglect for a short period of time. In general however, it is best if the soil is consistently moist. The tree will likely require watering at least once a day in the hottest part of the summer. Check your plant in the morning and the evening to make sure the soil is not dry any deeper than about a half inch below the surface.
Organic fertilizer is preferable for this tree; either a bonsai mix or a regular fertilizer diluted to half strength. Begin feeding on a weekly schedule throughout the first month after new buds appear. After this you can switch to feeding bi-weekly, taking a month-long break in August, then resuming bi-weekly feeding throughout the remainder of the growing season. No feeding is necessary after fall.
Styles – slanting, broom, informal upright, semi-cascade, cascade, twin trunk, group, and exposed root.
Hard pruning should be reserved for late winter, before new buds break, because Carpinus is a heavy bleeder once the sap begins to flow. Minor pruning may be carried out in early spring, after blooming occurs. This tree heals quickly from wounds and the younger branches respond very well to shaping by way of pruning. Once a shoot has five or six leaves, prune back to one set. Apical growth may need aggressive trimming as the apex tends to develop vigorously.
This specimen may be wired between spring and fall, although its twiggy branch structure is usually easily shaped by pruning alone. When wiring younger branches keep a close eye out for cutting in, as the growing season brings fast growth. Older branches respond well to anchoring. Branches may die off on this species as it ages, so keep this in mind when deciding your tree's design.
Leaves may be reduced by defoliation or by leaf pruning. They take well to leaf reduction, often being able to reduce to an inch long or shorter.
Korean Hornbeam may be propagated by seeds or cuttings. Sow seeds in moist soil in an outdoor bed in the fall. If planted while fresh, seeds should germinate the following spring.
For cuttings, take a three inch length from a mature tree, treat with rooting hormone and keep in moist, well-drained soil in a shady location until roots develop. These cuttings, if rooted successfully can sometimes flower in as little as one to two years, as opposed to several years for seedlings.
This may be carried out in early spring, every two to three years. Hornbeam tolerates aggressive root pruning – if necessary up to 30-40% of the mass may be removed. C. coreana prefers a container on the deeper side. They are fairly tolerant of different soil mixtures but a good blend is Akadama with Fujiyama potting soil.
Insects/Pests & Diseases
Korean Hornbeam is remarkably resistant to pests and disease. As with any bonsai, check your tree several times weekly for any signs of insects or spots on the foliage (which could indicate a fungal infection).