Water jasmine (Wrightia religiosa) bonsai

Placement

Water jasmine loves heat and full sun. Temperatures should not fall below 64 °F, so in a temperate climate it is an indoor bonsai for the cold season that benefits from a stay outdoors in summer. If the tree has been grown indoors, get it used to the sun gradually: give it two weeks in partial shade before full exposure. Sudden changes in light or temperature often cause leaf drop, so avoid moving it back and forth.

In fall, bring it into the house before the first cool nights and set it in front of the brightest window you have, ideally facing south in the Northern Hemisphere. Light falls off very quickly as you move away from the glass: a few steps are enough to deprive the tree of most of it. A grow light can be necessary to make up for the short days. In cooler conditions the tree can turn semi-deciduous and lose some of its foliage over winter. The dry air of heated homes does not suit it, so stand the pot on a tray of moist gravel. Misting, on the other hand, evaporates too quickly to make a real difference to humidity.

Soil mix

Choose a free-draining bonsai mix, because water must pass easily through the whole root ball. A blend of 50% akadama, 25% pumice and 25% lava rock is a good base; sift the akadama to remove the dust. In a humid climate, add lava rock to improve drainage; if you cannot check the tree often, a little more akadama will hold extra water. Akadama breaks down after about two years and the mix becomes less airy, one more reason not to put off repotting.

Watering

Water jasmine needs plenty of water. Water thoroughly as soon as the surface of the mix starts to dry: the mix must never dry out completely, but too much water is just as harmful. Do not water on a routine. Check with a finger about 0 in deep, then soak the whole root ball until water runs from the drainage holes, and repeat a few minutes later. Indoors, watering in the kitchen sink is convenient. Rainwater is ideal; otherwise tap water is fine.

Fertilizer: this is a hungry species that likes a high-nitrogen fertilizer. During the growing season, apply a solid organic fertilizer every four weeks or a liquid fertilizer every week. In winter, cut back to one feeding a month. A fertilizer higher in phosphorus helps promote flowering.

Pruning

Water jasmine buds readily along its branches after hard pruning. Prune heavy branches in spring, before strong new growth begins. To build fine ramification, let new shoots grow several leaf pairs, then cut them back to a single pair, and repeat with each new flush of growth. Flowers can appear once the third leaf pair has formed, so letting a few shoots grow longer encourages blooming.

In a tropical climate, the tree can be defoliated several times a year: this multiplies the twigs and reduces leaf size. Cut the leaves off leaving the leaf stalks in place, and defoliate only a tree in full health. Defoliating after root pruning also helps the tree cope with the stress. Never remove more than about one third of the foliage in routine maintenance pruning, and seal large cuts with cut paste; a concave cutter leaves a wound that heals better.

Wiring

Wire only young branches and fine twigs. Use wire about one third as thick as the branch, wound at 45° from base to tip; aluminum, which is softer, suits broadleaf trees. Growth is vigorous, so check the wire closely and take it off promptly, before it marks the smooth bark, which can happen within one to four months. Cut the wire at each turn instead of unwinding it. To position thicker branches, guy wires or strings are a good alternative: a thin wire or a cord anchored to the pot, a strong root or another branch, with padding under the tie.

Repotting

Check the roots every year and repot at least every two years, with substantial root pruning. Repot when the nights are warmest. Do not let the root ball become congested: once water no longer soaks in easily, the tree weakens very quickly. Tease out the old soil with a chopstick, cover the drainage holes with mesh, secure the tree with tie-down wires and work the mix in with the chopstick to fill any gaps. Water thoroughly, then keep the tree out of scorching sun and wind while it recovers, without feeding it right away. Its surface roots, naturally prominent, are one of its great assets.

Water jasmine is propagated from seed, from branch or root cuttings, and by air layering. Yellowing leaves are a common problem: they usually point to overwatering or underfeeding, although a single symptom can have several causes. Also watch for scale, mealybugs and aphids, and treat with a suitable product if they appear.