Bougainvillea bonsai

Placement

Bougainvillea needs full sun and heat to produce its bracts. During the growing season, keep it outdoors in the sunniest spot in the yard or on the balcony. When you move it out in spring, give it two weeks in part shade before full sun: this gradual transition avoids the stress of a sudden change. Under glass, in a greenhouse or sunroom, shield it from direct sun in midsummer.

It cannot tolerate any frost: it must spend the winter indoors or in a heated greenhouse. In fall, bring it in before nights drop below 50 °F. The ideal is a cool, bright room, never below 50 °F and preferably no warmer than 59 °F, which is hard to achieve in many homes. Light remains essential: place the tree right against the brightest window or add a grow light. It will survive a colder but frost-free winter if the mix is kept dry, at the cost of losing its leaves.

Soil mix

A standard, free-draining bonsai mix suits it. The mix must hold enough water between waterings, drain the excess immediately and stay airy. Bougainvillea prefers a slightly acidic pH, around 6 to 6.5. Sift the mix to remove the dust so it stays airy and drains well.

Watering

Water thoroughly as soon as the mix has dried, never leaving water standing. Constantly soggy mix leads to root rot, fungal problems, greater susceptibility to pests and, eventually, the death of the tree. Bougainvillea also blooms better when kept a little dry than when watered generously. Do not water on a fixed schedule: feel the mix. After flowering, water less often; in a cool winter spot, water rarely but deeply. Avoid very hard, lime-rich water.

Fertilizer: during the growing season, a solid organic fertilizer once a month or a liquid fertilizer every week; in winter, a liquid fertilizer every two weeks. Avoid excess nitrogen, which pushes leaves at the expense of bracts; once the bracts start to color, a high-potassium fertilizer supports them.

Pruning

Bougainvillea grows fast, takes pruning very well and suits most bonsai styles. It flowers on the current season’s growth, so the balance between shape and bloom comes down to when you cut.

• After flowering: shorten shoots, leaving just two leaves on each.
• Twigs and branches: prune them in fall or winter.
• Hard pruning: the tree buds back from old wood after a heavy cut.
• In summer: if you want flowers, do not pinch or trim too much in this season.
• Wounds: seal large cuts with cut paste; they heal slowly.

Cut off faded bracts and flowers so they do not rot on the tree. Wear gloves: the twigs are armed with sharp thorns.

Wiring

Young shoots and twigs wire easily. Older branches, however, become very stiff and snap easily: do not try to bend them hard. For those, a guy wire anchored to a strong root, another branch or the pot, with padding under the wire, lowers the branch without coiled wire. Watch out for thorns while applying wire.

Choose aluminum wire, which is easier to handle, about one third the thickness of the twig, and wrap it at about 45°. Check often: in active growth, the twig can thicken and be marked within one to four months. Remove the wire before it cuts into the bark, cutting it at every turn. Avoid wiring a weak or freshly repotted tree.

Repotting

Repot small bougainvilleas every two or three years and large specimens every three to five years, in early spring, into a standard free-draining mix. The roots are yellow, thin and fragile: ease the root ball out of the pot carefully so you do not tear them, untangle them gently and do not use the root rake with force. Root pruning is well tolerated; remove no more than about 30% of the roots. After repotting, keep the tree in stable conditions, with no fertilizer or hard pruning until it starts growing again.

Bougainvillea is propagated from semi-hardwood cuttings or root cuttings in spring and summer, and by air layering. Semi-ripe cuttings taken with a heel in summer usually root in four to six weeks, faster with bottom heat of about 59 °F; layering in late winter and early spring is often the most reliable method. A healthy tree, kept from soggy soil and given good light, resists pests well. When weakened, it can suffer from powdery mildew, aphids, scale, mealybugs, whiteflies, spider mites or caterpillars: treat with a suitable product and correct its growing conditions.