In 2001 we visited Singapore to view and study their bonsai. Lim Keow Wah, William Koh, Wai Hong Yam, and Kwei Foon Chai as well as other members of the Singapore Penjing and Stone Appreciation Society were gracious hosts and escorted us around their country. With their help we were able to tour some of Singapore's public gardens, many of which contain beautiful bonsai, as well as allowing us access to private bonsai collections.
The number of species used for bonsai in Singapore is impressive, and the quality of the trees is superb. Many plants from different parts of the world, as well as species native to Singapore and the surrounding countries, are being used for bonsai. We observed several species that have rarely been documented in the bonsai literature. One that we feel is particularly worthy of mention is Caesalpinia ferrea also called the Leopard tree or Brazilian Ironwood. It originates from eastern Brazil. Its hard wood and mottled bark undoubtedly give rise to the common name of Brazilian Ironwood.
Caesalpinia is in the legume family of plants, and there are 70 or more species of Caesalpinia in the tropics and subtropics. The leaves are alternate, with leaflets in 4-8 pairs and flowers in racemes or panicles. Caesalpinia ferrea grows to 50 feet in nature. A fairly large number of Caesalpinia species also exist as native plants in the Southeast USA and Mexico. Some of these other Caesalpinias are used as landscape trees, and find occassional use as bonsai. In their natural environment Caesalpinias are well adapted to heat, dryness and low fertility soils .
The bark of the Caesalpinia ferrea is the single most attractive feature of the plant. In the landscape the trunk flows smoothly and gracefully, and the bark is a patchwork of chocolate brown, off-white, and green patches in a mottled pattern which likely gives rise to the common name of "Leopard Tree". The old outer bark gradually darkens to a chocolate brown but in active growth the bark is shed and lighter colored white, brown, and green patches result. Trees that grow slowly or are weak will not have multi-colored bark and are uniformly dark in color.
The tree has a compound leaf. In container culture, the leaves can be kept quite small, and individual leaflets will be smaller yet.
The seed is a brown or black waxy seed contained in a typical legume seed pod, see photo.
The plant is also delicately twiggy which gives it good bonsai character. Another outstanding feature is its thin, layered foliage allowing a penetrating view into the branch structure thus giving the tree an air of delicacy.
Due its fast growth, removal of wire from branches at the appropriate time is mandatory to avoid scarring. Wire scars will heal well if the tree is allowed rampant growth .
Caesalpinia can also withstand severe root trimming without harm. If this is done I recommend that the tree be placed into a plastic bag to keep humidity high until the tree recovers. Keep it out of direct sun during this time. As an older bonsai some specimens may develop unique knobby lumps on the exposed basal roots. This can add to the charm of the composition. Rootage on many specimens is rather one sided, creating unbalanced roots systems. Great care must be used to overcome this growth habit for more formal bonsai styles.
Caesalpinia is tolerant of heat, dryness and is a survivor in pot culture. With severe reduction the tree springs back with new life even from older wood.
The Leopard tree's negative features are the compound leaf, long internodes, and the habit of folding its leaves up at night or when the tree is roughly handled. The total leaf size is 4.75 inches in length and the individual leaflet is up to one inch, but in a potted specimen this reduces to a full leaf 1/2 inch in length, and a leaflet 1/8 inch. At maximum growth internodes are three inches in length and less than 1/8 inch in pot restricted specimens. When the plant needs to achieve a finished appearance, leaf size is easily controlled .
Once the desired trunk size is reached, internodes are kept short by diligent pruning, and restraining the plant in a smaller container. The compound leaf is likewise reduced by keeping the plant in a small pot and by shortening each leaf by cutting it back to the first leaflet section. Since the individual leaflets are small this works very well keeping the plant in scale even with small trees.
The blooms of the Caesalpinia ferrea are dark yellow and displayed in a panicle or raceme. Caesalpinia have not bloomed for us in pots, but perhaps with older trees this may be possible.
The plant is easily propagated from seed. The seed may be quickly germinated by nipping the hard outer coat with a nail clipper and placing them to soak overnight in water. Plant the seed in bonsai soil and in a day or two the sprouts will be up and growing. Seed is available via the internet from a number of seed suppliers.
Cuttings have been successful. Use older wood, with mature bark, rather than green shoots and dip in a rooting hormone. Place the cuttings into bonsai soil, keep the soil moist and in a humid place. Success will vary from 20 to 90 percent depending on the plant's vigor. Strongly growing trees will root the best; avoid trees in weak condition or going into dormancy.
Air layers can be done but may take months to become properly rooted. The tree will try to heal over the wound so make the layer trough large and deep. Repeated re-wounding may be needed until the layer succeeds in producing roots.
The plant is fool-proof and very rugged in pot culture. It is happy in any moisture retaining but well draining soil. Use a 25/75% mixture of inorganic material to organic in the soil mix. Trees obtained from landscape nursery stock can be severely reduced to produce bonsai.
Do not ever let the tree dry out. It will die or suffer severe twig die-back.
A four foot tall landscape tree was reduced to 24 inches, and then regrown . The picture below shows it growing after its initial reduction.
The tree above had the top airlayered and removed. The bottom sprouted out from the trunk. See pictures below.
Caesalpinias are fertilized as any other bonsai.
Insects have not been a problem.
For best growth full sun is advisable. In Singapore the bonsai may be kept in full sun with adequate watering, but the plant also grows very well under artificial conditions with grow lights.
Dry air or high humidity are well tolerated.
Caesalpinia ferrea is a marvelous material for bonsai. We have become convinced that it is a very worthwhile addition to the list of plants useful for tropical and indoor bonsai, and wish to encourage its more widespread use. We hope this will stimulate others to give the species a try, and to further develop its full bonsai potential. Special thanks to our Singapore friends for bringing this tree to the attention of the bonsai world.