Serissa

Identification and origin

Serissa japonica belongs to the Rubiaceae, the coffee family. It is native to south-central and southeastern China and to Taiwan, where it grows in woodlands, along streambanks and in wet meadows. It has been introduced and has naturalized in many parts of Asia, as far as Japan and Korea, as well as in Madagascar. Its epithet japonica recalls Japan, but current classification considers it introduced there. It is still often sold under its old name, Serissa foetida.

It is a dense shrub that forms a dome 2–4 ft tall and 3–5 ft wide. Its fine, rather wiry green stems carry opposite, simple, oval leaves that are leathery and glossy and only 0–1 in long. Depending on the climate, it stays evergreen or drops its leaves. The light gray trunk becomes rough with age.

The flowers, about 0 in across, are white and star-shaped, with a tubular base and four to six spreading petals. They open from pink buds, singly or in small clusters, in the leaf axils or at the tips of the branches, and follow one another abundantly from spring to fall. They attract bees and other pollinators.

A notable quirk: crushed or cut leaves and roots give off an unpleasant smell, which explains the old name foetida.

Several cultivars exist:

• ‘Variegata’ and other variegated forms: deep green leaves edged in yellow;
• ‘Kowloon’;
• ‘Apple Blossom’;
• ‘White Swan’.

Light

Serissa likes bright but softened light: two to six hours of direct sun a day, preferably in the morning, with protection from the scorching afternoon sun. In summer it benefits from a sunny spot outdoors, sheltered from wind. Indoors, place it near a bright window. The warmer the room, the more light it needs; in winter a grow light can make up for short days.

It does not take well to being moved: choose a stable spot and do not move it without a reason. A sudden change in light or temperature is often enough to trigger leaf drop.

Watering

Serissa needs steady moisture without excess. The root ball should never dry out completely, but it should not stay soggy either, or the roots will rot. Water as soon as the surface of the mix starts to dry, thoroughly, then empty the saucer. Needs vary a lot with heat, light and pot size: feel the mix rather than following a calendar.

It prefers water with a neutral pH, so avoid very hard water. Outside the flowering periods, misting with lime-free water raises the humidity, which it enjoys. If the shrub drops its leaves after a change in conditions, keep watering, but a little less, while it recovers.

Potting mix

It needs fertile soil, rich in organic matter, moist but well drained, with a neutral pH. In the ground, in mild climates, it suits borders, foundation plantings, low hedges and the edges of walkways. In a container, a good-quality potting mix lightened with draining material works; for a bonsai, a standard bonsai mix is fine. The pot must always have drainage holes.

Temperature

Serissa is grown in the ground in USDA zones 7a to 11b, that is, down to about -0 °F. In the colder zones it does not stay evergreen: it drops its foliage when the temperature falls below about 39 °F.

In a container, and above all as a bonsai, it dislikes frost and sudden swings. It can spend the warm season outdoors as long as nights stay above 50 °F. From fall to spring, keep it indoors or in a heated sunroom between 50 °F and 68 °F. It prefers stable temperatures: keep it away from radiators, open doors and cold air currents.

Repotting

Repot a young plant about every two years, in spring, in a fresh, well-drained mix. Prune the roots only moderately: they give off an unpleasant smell when cut, which is normal. After repotting, keep the shrub out of direct sun and wind for a few weeks and wait for it to recover before feeding.

Pruning

Serissa tolerates hard pruning, best done in early spring if needed. To keep a compact habit, let a shoot form four or five leaves, then cut it back to two. A plant in bloom is pruned lightly; it is cut back more firmly after flowering. Every two or three years, shorten the branches back to old wood to keep a dense outline.

In the ground it naturally forms a neat dome and lends itself to shaping as a low hedge or edging.

Propagation

• Cuttings: semi-hardwood cuttings, taken from current-season shoots as they begin to firm up, root easily.
• Root cuttings: also a recommended method for this shrub.

Young plants need the same stability as mature ones: soft light, steady moisture and constant warmth.

Common problems

The same symptom can have several causes: leaf drop can come from a move, a cold snap, irregular watering or a pest. Look at the plant and its location before treating anything.

• Leaf drop: a typical reaction to a change of place, light or temperature. Restore stable conditions and be patient.
• Spider mites: favored by dry air; raise the humidity around the plant.
• Aphids, root aphids and woolly aphids: watch young shoots and the root ball.
• Scale: small shields stuck to the stems.
• Powdery mildew: a white coating on the leaves.
• Root rot: caused by overwatering or a poorly draining mix. Unpot, cut away damaged roots and replant in fresh, free-draining mix.

Toxicity

No toxicity is reported for dogs or cats: serissa does not appear among the plants listed as toxic to these animals. Still, keep children and pets from chewing on it.