Natal plum bonsai

Placement

Carissa macrocarpa comes from the coastal thickets and dunes of eastern and southern Africa. It loves warmth and light: place it where it gets at least four to six hours of direct sun a day. Outdoors, it easily handles full sun, wind and even salt spray. Indoors, choose a south-facing window or supplement the light with a grow light: insufficient light shows up as soft growth and poor flowering.

It is sensitive to frost. In a mild climate it can live outdoors year-round; elsewhere, put it outside during the growing season and bring it in before the first frosts, to a bright room or a greenhouse, until mild weather returns. In the ground, a well-established plant can take brief, light frosts, but young plants suffer as soon as the temperature nears 28 °F; in a pot, with a reduced root ball, take no chances.

Its forked thorns, sturdy and sharp, call for gloves and a bit of care every time you work on it. Any cut beads up with a white latex, considered harmless.

Soil mix

Use a free-draining bonsai mix that still holds a little moisture. In the wild, the species grows in sandy soils, and its roots rot in poorly drained soil: avoid an overly organic substrate that stays wet. The pot must have adequate drainage holes. It tolerates a slightly alkaline substrate well, but a very alkaline soil can cause micronutrient deficiencies, visible as yellowing leaves.

Watering

Water regularly, but only after checking the moisture of the substrate: it should dry slightly between waterings. When it has, water deeply until water runs out of the drainage holes, then let it drain. The species likes moderate moisture but cannot tolerate waterlogging, the main cause of root rot. In hot weather, watering becomes more frequent; in winter, when growth slows, space it out. It withstands short dry spells well, which makes it forgiving of the occasional missed watering.

Fertilizer: from spring to early fall, a balanced fertilizer, solid or water-soluble, every four to six weeks depending on the product chosen. A small dose before growth begins stimulates new shoots. Do not fertilize during the winter rest. Too much fertilizer produces weak growth and excess foliage at the expense of flowers.

Pruning

Pruning maintains the shape and makes the branching denser. Prune preferably after the main flowering: remove dead or damaged wood, crossing branches and those growing toward the inside of the canopy. Regularly shorten new shoots and pinch the tips of the twigs to multiply the ramification and get a compact, bushy canopy. Maintenance pruning is possible year-round, but avoid severe pruning right before and during flowering so you do not jeopardize the flowers.

Dwarf cultivars, such as ‘Nana’ or ‘Boxwood Beauty’, are well suited to container growing and bonsai. On these, watch for vigorous shoots that suddenly shoot up and distort the silhouette: cut them off without delay. Thanks to its dense foliage and toughness, the Natal plum lends itself to a variety of styles.

Wiring

Like most species, it can be wired at any time of year. Preferably use anodized aluminum wire, easier for a beginner to handle, about one third the thickness of the branch, wound at roughly 45°. First wire everything you want to shape, then bend while pressing on the inside of the curve to avoid splits, without going back over the same branch several times. Branches thicken quickly in summer: check often and remove the wire as soon as it starts to mark the bark. Keep your gloves on throughout: the thorns are numerous.

Repotting

Repot every two to three years, preferably in early spring, before new growth starts. Gently remove some of the old substrate, cut away dead roots and lightly prune the others to keep a compact root system. Set the tree in a fresh, free-draining mix, water generously, then place it in the shade for a few days while it recovers.

It is propagated from seed, cuttings or air layering. Semi-ripe cuttings, taken from late spring to early summer, dipped in rooting hormone and kept in a closed, humid environment, root in four to six weeks. Seeds, sown in a free-draining mix kept warm and moist, take several weeks to germinate.

The tree is quite resistant to pests, but aphids, mealybugs, spider mites and scale insects can settle in: treat with insecticidal soap or neem oil. In humid conditions, powdery mildew can appear; good air circulation and removing dead leaves prevent it. The small red fruits, edible but tart, are best enjoyed as jam.