Chinese sweet plum

Identification and origin

Sageretia thea belongs to the Rhamnaceae, the buckthorn family. Its native range is very wide: from Eritrea and northern Somalia to the Arabian Peninsula, from Iran and Central Asia to the Himalaya, and from central and southern China to the Malay Peninsula, Korea, Japan and Taiwan. It has become naturalized in Texas. In China it grows in mountain forests, thickets and on hills, up to about two thousand one hundred meters. The genus, with some thirty-five species, honors the French botanist Auguste Sageret; the epithet thea recalls that its leaves were used as a tea substitute. It is still often sold under its synonym Sageretia theezans.

It is an upright or somewhat scrambling shrub that reaches 6.5–10 ft tall. Its slender brown twigs, finely hairy when young, often end in a spine. The leaves, opposite at the base of the twigs and alternate higher up, are elliptic to ovate, finely toothed, 1–2 in long in the wild, light green and glossy; new growth is reddish. They stay on the plant in mild climates but drop where winters are cool. The bark, smooth and dark brown, peels away in irregular patches to reveal light brown wood, a little like sycamore bark.

Small, fragrant, yellowish flowers in loose spikes appear in summer and into early fall. They are followed by small drupes about 0 in across, black to purplish black when ripe, with sour flesh, which ripen the following spring.

Light

It likes bright light but not scorching sun. Outdoors, morning sun with afternoon shade is ideal: it tolerates full sun, but then it drinks far more and can scorch if it has not been moved into the sun gradually. Indoors, keep it by a very bright window, shielded from direct afternoon sun through the glass. The warmer the room, the more light it needs; a grow light can make up the difference.

Watering

This is the tricky part. The root ball should stay moist but not soggy and must never dry out completely: a shrub that wilts struggles to recover, and a single missed watering can be fatal in a small pot. Check the moisture every day by pushing a wooden chopstick into the soil, and water as soon as it comes out nearly dry, rather than on a fixed schedule.

Use water low in lime, such as rainwater: hard water eventually causes chlorosis. It enjoys high humidity. Indoors, stand the pot on a tray of damp gravel and mist the foliage often with lime-free water.

Potting mix

In a container, use a mix that holds enough water while still draining well, such as a basic bonsai mix. Some growers get better results with a mix that includes some peat. A pot slightly larger than usual dries out more slowly.

Temperature

Chinese sweet plum does not tolerate prolonged frost. It can only be grown in the ground from USDA zone 8 upward: below 25 °F the fine twigs die back, and harder cold kills whole branches, although the shrub often regrows from old wood or the roots. In a pot, move it outside once nights stay above 41–43 °F and bring it in before the first cold spells. In winter, keep it between 54 °F and 72 °F, in a cool, bright room or a heated sunroom; keep it above 50 °F so it keeps growing. It readily drops its leaves below about 55 °F, and it also suffers from constant dry heat: a cooler spell at night does it good.

Repotting

Repot about every two years, in spring, into fresh mix. It tolerates root pruning well: remove at most about a third of the roots. A very vigorous plant whose roots fill the pot quickly can need repotting more often.

Pruning

It is very easy to prune: shoots can be cut back to two leaves in any season, and it buds freely from old wood after heavier pruning. Frequent trimming builds dense branching. Still, let a young plant grow 4–6 in before cutting it back so the trunk can thicken; the trunk fattens slowly. Avoid pruning in late summer if you want flowers and fruit. In the garden it also makes a clipped or informal hedge.

Propagation

• Cuttings: both softwood and hardwood cuttings root easily during the growing season. They can even root in a glass of water in two to four weeks, with no rooting hormone.
• Seed: seeds need no cold period and can germinate in any season.

The thick-trunked plants sold as bonsai are usually grown in the ground in China for many years.

Common problems

A single symptom can have several causes: leaf drop can come from cold, poor light, a dry spell or a pest. Look at the plant and where it stands before treating.

• Aphids and whiteflies: common under glass; higher humidity helps keep them down.
• Mealybugs: they hide under the flaking bark.
• Spider mites: indoors, in dry, stuffy air.
• Fungus gnats: they thrive in soil that is always moist.
• Powdery mildew: rare; improve air circulation rather than lowering humidity.
• Pale green leaves with darker veins: iron deficiency, often caused by hard water.
• Wilting: the root ball has dried out; a weakened plant might never recover.

Toxicity

No toxicity has been reported for dogs or cats: Chinese sweet plum does not appear among the plants listed as toxic to these animals. Even so, keep children and pets from chewing on it, especially since the twigs are spiny.