This report on the tree of the month was taken from the Potomac Bonsai Association "Clippings" - Newsletter. Volume 35, Number 9 September 2006. It is used with permission - ED.

Scientific Name: Carpinus caroliniana
Common Name: American hornbeam

The American hornbeam, also called Blue beech, Water beech, or Ironwood, is actually a member of the beech family. Related species commonly used for bonsai include the Japanese loose-flowered hornbeam (C.laxiflora), the European hornbeam (C.betula) and the Korean hornbeam (C.coreana) or (C.turkzaninowii).

The hornbeam is an under-story tree, living in the shade of others in the forest. It will grow with an attractive open habit in total shade, but will have dense growth in full sun. The muscle-like bark is smooth, gray, and fluted. Its leaves are similar to the beech, but are narrower and more distinctly veined. They grow alternately on the shoot, in almost all directions. The buds are also shorter than those of the beech. Fall color is faintly orange to yellow before falling early. Brown leaves occasionally hang on the tree into winter.

Hornbeams are easily collected because they do not root deeply in the rich forest soil. When collecting, leave as much soil as you can on the root ball. Incorporate some of the collected soil into your growth medium to continue the cycle of mycorrhiza.

• Potting information: Publications differ as to the depth of containers for hornbeam bonsai. My personal belief is that the depth does not matter if you use a soil rich in humus and the bonsai is never allowed to dry out. Containers can be glazed or unglazed, depending on fall color. If the tree is richly colored, a glazed container will work.
• Light requirements: Hornbeams can be grown in full sun if they are potted in a humus-rich soil in a somewhat deep container and kept evenly moist all of the time. Hornbeams in shallow containers should be grown in partial shade in summer.
• Temperature: Fairly cold-hardy - Zones 3 through 9A.
• Watering: Increase in summer - Never let soil dry completely.
• Repotting: Young trees every 2 years; trees 5 years or more every 4 to 5 years. Use regular bonsai soil with extra humus.
• Feeding: Feed with balanced (20-20-20) half strength, every 2 weeks May-June. Do not fertilize July-August. Resume fertilization September-November (5-10-10). Do not feed for 2 months after repotting.
• Pruning: The best time for minor pruning is early spring. Prune back to the first pair of leaves on new shoots. Developmental (heavy) pruning should be done in late winter. Hornbeam is apically strong, so radical pruning may be necessary from time to time, along with conservative pruning on lower portions of the tree for balance. Defoliation may or may not work according to some writers. My experience has been good if done in early June.
• Propagation: From seed, cutting, and airlayering.
• Pest & Diseases: Relatively free from disease. Fungi cause leaf spots, but are not serious. Aphids are a problem in the spring.
• Bonsai styles: Almost any style suits the hornbeam, mainly upright styles. Sometimes a tree collected at a stream bank will lend itself to a cascading style, but that's rare. Trees should show inner structure rather than being a dense head of foliage. Pruning cuts that seal over give the trunk the appearance of age and add to its character.

Bibliography:
Brockman, C. Frank, Trees of North America,
Golden Press, 1968
Owens, Gordon, The Bonsai Identifier,
Chartwell Books, 1990
Pottberg, Clifton, Hornbeam ,PBA Newsletter's
Tree of the Month 1972, PBA, 1980
Preston, Richard J. Jr., North American
Trees, MIT Press, 1978
Zane, Thomas L. Seasonal Trees,
Rappahannock Bonsai
Society Newsletter, Summer 2006