Chinese Elm Bonsai Care Guide
Ulmus parvifolia is a climate-tolerant native of Taiwan, China, and Korea. In nature these trees can reach a height of 60-70 feet and may live 100 years or more. Sometimes confused with Zelkova – Japanese Elm – the two can be differentiated by their fruits and leaves.
The Chinese Elm has winged fruit, whereas the Japanese Elm has unwinged, and Chinese Elm has double-toothed leaves compared to the single-toothed leaves of Japanese.
Ulmus is an excellent bonsai tree and is sometimes referred to as being almost impossible to kill, making it a good choice for beginners. There are several varieties, all appropriate for the art-form. These trees may be evergreen or deciduous, depending upon their environment.
The leaves of this Elm are small, a desirable trait for shaping purposes. The trunk is typically slim, with bark that varies significantly among the different types.
'Hokkaido' is a favorite among enthusiasts for its corky bark, fast growth, and tiny leaves. It is one of the more delicate cultivars so be very cautious when wiring.
'Dynasty' is also a great choice, with small leaves and smooth, gray bark. If allowed to be deciduous, the leaves on 'Dynasty' will turn red in autumn.
This tree prefers full sun, or partial shade at the most. Varieties with smaller leaves must have full sun, and bonsai with full ramification may experience shoot dieback if in shade too long. Chinese Elm is hardy, tolerating temperatures to 20 degrees F. If concerned about severe cold, insulate the pot or mulch it into the ground to protect the sensitive root system.
If kept indoors this species may remain evergreen, but when outdoors in areas that have a winter it will likely drop leaves like a typical deciduous. Whether indoors or out, adequate sunlight is essential. In excessively hot climates, the pot itself may be shaded while allowing the tree to be in sunlight.
Ulmus does like water but still, the roots should not be allowed to remain continually soaked. Too much or too little water may be tolerated occasionally but generally the roots should just be kept moist. As for most bonsai, rainwater is optimal as it is free of chemicals.
Chinese Elm is a fast-growing species, and proper feeding will encourage vigorous foliage growth. After budding occurs in spring, fertilize with a mix high in nitrogen for about a month, then switch to a balanced bonsai fertilizer, administered monthly throughout the growing season. In autumn and winter feed a low N blend.
Clip and grow is a reliable method of training this tree. One of the beauties of the use of the species for bonsai is that it is readily manipulated and foliage growth lends itself well to shaping via trimming. Fine ramification is fairly easy to achieve and the leaves take well to reduction.
Hard pruning will stimulate copious new growth, although larger branches should be cut in late summer to fall in order to minimized scarring. The bark is fragile and combined with the tree's growth rate, wires can cut in very quickly. The shoots do hold their adjusted shape, making wiring an attractive training option, just be sure to check the wires frequently.
May be done by seed, outside in fall or spring, or cuttings – softwood in summer and hard cuttings in winter. Air-layering is quite easily accomplished with these Elms and should be done after hardening of spring growth. The dwarf cultivars can only be propagated through layering or cuttings. Take cuttings from new growth, early in summer.
Spring is the best time for repotting and should be done before the buds open, allowing for more aggressive root trimming. The roots of Ulmus grow quickly and the plant does not like to be root-bound, so you may have to repot every one to two years. While repotting, wash the root pad in order to have a clear view of the root ball. This species has pulpier roots than most bonsai and they can be crushed easily, so take care and approach root pruning with an organized plan.
The key to avoiding root rot in this tree's sensitive root system is to pot it in well-draining soil. As long as there is good drainage and the roots have plenty of growing room, most mediums will do.
Insects/Pests & Diseases:
Chinese Elm is a hardy species as far as pests go. The tree may come under attack from aphids but if caught early, rinsing them off with water will usually suffice. If the tree retains too much moisture through either extended wet weather or over-watering, it may experience black spot fungus. A general fungicide is effective for this problem, just use judiciously as the leaves may burn.