Star jasmine

Identification and origin

Trachelospermum jasminoides belongs to the dogbane family, Apocynaceae, not to the family of true jasmines (Jasminum, Oleaceae). Its natural range stretches from Tibet to Japan: central, southern, and southeastern China, Hainan, Taiwan, Korea, and Vietnam. The genus name comes from the Greek trachelos, neck, and sperma, seed; the epithet jasminoides means “resembling jasmine.”

It is an evergreen woody vine that twines around its supports. Its opposite, oval, leathery, glossy leaves reach 4–4 in long: bronze-purple when young, then lustrous dark green, they often take on bronze-red tones in winter. A broken stem or leaf stalk oozes a sticky white latex.

The flowers, about 1 in across, open in clusters at the leaf axils and the tips of the shoots: creamy white and shaped like a small pinwheel with five twisted lobes, they give off a sweet, jasmine-like scent and attract bees. The main bloom comes in late spring or summer depending on the climate, with a few flowers later on. The fruits, long pods borne in pairs, rarely form where summers are short.

Trained on a support, the plant reaches 13–19.5 ft, sometimes much more over the years. Without support it becomes a groundcover or sprawling shrub 18 in – 2 ft tall and 4–5 ft wide. The cultivar ‘Madison’ is known for better cold hardiness; there are also selections with variegated foliage, such as ‘Variegatum’, and others with pale yellow flowers.

Light

Outdoors, plant it in sun or partial shade, ideally against a south- or west-facing wall or fence. It tolerates more shade, but then grows thinner and blooms less.

In a sunroom or indoors, give it bright light filtered by a sheer curtain, and protect it from hot summer sun through glass, which can scorch the leaves. In winter, on the other hand, it needs at least four hours of direct sun a day.

Watering

After planting, water regularly for at least the first year while the roots establish, then only during dry spells: once established, it is fairly drought-tolerant. The soil should stay evenly moist without becoming soggy.

In containers the root ball dries out quickly, so check the moisture of the mix often in summer and do not let it dry out completely. In winter, watering is rarely needed outdoors, but keep an eye on plants in pots and in sunrooms.

Potting mix

It wants fertile, well-drained soil, preferably neutral to alkaline, though it copes with slightly acidic soil. Adding leaf mold at planting time helps. Avoid heavy, clay, or waterlogged ground, where it is prone to root rot.

In containers, use a rich, free-draining, peat-free, soil-based mix. Mulch around the base in spring or fall with a thick layer of well-rotted compost spread on moist soil, leaving 4 in clear around the stem. In fertile soil, fertilizer is rarely needed; one feeding in spring is enough if the leaves turn yellowish or the soil is poor. Container plants, however, benefit from regular feeding during the growing season.

Temperature

Star jasmine is grown in the ground in USDA zones 8a to 10b. It withstands moderate frost, down to 14–23 °F, if it is planted in a spot sheltered from cold, drying winds. In a pot its roots are more exposed, so do not let it go below 23 °F. During cold snaps the leaves can redden, develop spots, or drop; the plant then recovers, except in the harshest winters.

In cold regions, grow it in a container so it can come indoors for winter, or keep it in a sunroom or greenhouse year-round. Outdoors in winter, mulch the base thickly, wrap the pot with insulation, and cover the plant with frost cloth during hard freezes.

Indoors it does well with days around 68–72 °F and cool nights between 50 °F and 55 °F.

Repotting

Plant or repot preferably in spring, ahead of the growing season. For containers, choose a large pot with drainage, fill it with a soil-based mix, and set up a sturdy support from the start, such as a trellis or taut wires, to tie the stems to: the plant is long-lived and needs a robust support. Container growing has another advantage: it lets you move the plant to shelter for the winter.

Pruning

Star jasmine needs little pruning. Guide and tie young stems to their support until they twine on their own; it will not cling to masonry. Pinch the shoot tips to encourage branching. If needed, prune right after flowering to keep it in bounds, or in spring to remove tangled, weak, or damaged stems.

An overgrown plant can be renovated in spring by cutting stems back by two-thirds, just above a side shoot. When it is grown as a groundcover, trim off the stems that try to climb. Clean your tools after pruning, because the milky sap sticks to the blades.

Propagation

• Layering: in spring, bend a flexible stem down to the ground, bury a section of it held in place with a pin, and let it root before cutting it from the mother plant.
• Semi-ripe cuttings: in summer or early fall, take pieces of the current year’s stems whose base is starting to firm up. They root best in a heated propagator with bottom heat of 59–68 °F.

Growing from seed is rarely possible, because seeds seldom form where summers are cool.

Common problems

• Yellowing leaves: poor soil or lack of fertilizer.
• Leaves turning red, spotted, or dropping in winter: a cold snap.
• Decline: root rot (phytophthora) in heavy, clay, or poorly drained soil.
• Few flowers, sparse growth: shade that is too dense.
• Pests: scale insects, including cushion scale, as well as mealybugs, spider mites, and whiteflies, especially under glass or in very hot spots. Japanese beetles can feed on the foliage where they occur, and rabbits browse it; deer, on the other hand, leave it alone.
• Honey fungus: this root disease can attack the plant.

The same symptom can have several causes: look at exposure, soil moisture, recent temperatures, and the condition of the roots together before drawing conclusions.

Toxicity

Star jasmine is listed as non-toxic to dogs, cats, and horses. It is, however, classed among plants considered poisonous to people if eaten, without the substance involved being specified. As a precaution, keep children from chewing the leaves or stems, and if any is swallowed, contact a poison control center.