Bougainvillea

Identification and origin

Bougainvillea glabra belongs to the Nyctaginaceae, the four-o’clock family. It is native to northeastern, southeastern and southern Brazil and has naturalized in many warm regions of the world, including Hawaii, Texas and Florida. The genus honors the French navigator Louis-Antoine de Bougainville; the species name glabra comes from the Latin for “bald.”

It is a fast-growing evergreen climbing shrub that reaches 10–19.5 ft tall and 6–10 ft wide. It does not cling on its own: its long stems, armed with curved thorns, sprawl over their support and must be tied to a trellis, fence, wall or pergola.

• Leaves: alternate, oval to lance-shaped, glossy green, sometimes variegated, usually smooth but occasionally slightly hairy.
• Bracts: what look like flowers are modified leaves, pink, purple or red in the species; cultivars also come in white, orange, yellow or double forms.
• Flowers: small, tubular and usually white, in the center of the bracts, from summer into fall when the plant gets enough light and heat.
• Stems and bark: thorny; the gray-beige bark becomes furrowed and gnarled with age.

It differs from great bougainvillea, Bougainvillea spectabilis, by its distinctly five-angled floral tube and shorter bracts; the latter has a rounded tube and longer bracts. B. glabra and the hybrid B. × buttiana are the best choices for containers, because they bloom while young.

Light

Sun is the key to flowering: the more direct sun the plant gets, the more bracts it produces; without direct sun, it will not bloom. Outdoors, give it full sun; it tolerates light shade at the cost of fewer blooms. Under glass, in a greenhouse or sunroom, shield it from direct sun in midsummer.

Watering

Native to dry climates, bougainvillea blooms best in soil kept on the dry side: water deeply, then wait until the mix has dried before watering again. Once established in the ground, it is quite drought tolerant. Overly generous watering holds back flowering and encourages root rot.

In a container, match watering to the season rather than a schedule. Increase it in late winter, when light and warmth restart growth, then water freely during active growth, always letting the surface dry. In bright weather, humid air helps the buds break. After flowering, water less often; in winter, water rarely but thoroughly, keeping the mix fairly dry.

Potting mix

In the ground, it accepts clay, loam, sand or soils rich in organic matter, as long as they drain well. It prefers acidic to neutral soil: in alkaline soil the foliage yellows from chlorosis. In a container, use a peat-free, loam-based mix and a pot with good drainage holes. When planting in a sunroom bed, enrich the soil with compost and a balanced fertilizer.

Fertilizer: during active growth, feed weekly with a high-nitrogen liquid fertilizer; as soon as the bracts show color, switch to a high-potassium feed. Once they have dropped, another round of nitrogen encourages a second flush. Avoid excess nitrogen, which produces leaves at the expense of bracts, and stop feeding when flowering ends.

Temperature

Bougainvillea is hardy in USDA zones 9a to 11b and does not tolerate frost. In a container it can summer outdoors, ideally with nights of 64–70 °F and slightly warmer days. Bring it in before the first frost and keep winter nights at 50 °F or above, with days a few degrees warmer. It will survive a colder but frost-free winter if the mix stays dry, at the cost of losing its leaves.

When the bracts show color, a cooler spot, around 50 °F if possible, with good ventilation and no direct sun, makes them last longer. The leaves can droop for a few days: water a little less while the plant adjusts.

Repotting

Repot if needed in early spring, into a peat-free, loam-based mix. On bonsai, the yellow, thin, fragile roots tear easily: untangle them gently.

Pruning

Bougainvillea blooms on the current season’s growth. Prune in late winter or early spring, just before growth resumes. Avoid pruning too much or too late in the season: every cut removes future bracts.

• Training: early in the season, bend and tie in vigorous young side shoots; this checks their vigor and stimulates bract formation.
• Second flush: after the bracts fall, cut long growth back by half for a second round of color in late summer.
• Forms: it can be trained on a pillar or trellis, as a standard, or spur-pruned to restrict its size; it is also styled as bonsai.
• Hard pruning: it resprouts even from old wood, but a very old, worn-out plant is usually better replaced.

Wear heavy gloves: most cultivars have sharp thorns.

Propagation

• Semi-ripe cuttings: in summer, taken with a heel; they root in four to six weeks, faster with bottom heat of about 59 °F.
• Hardwood cuttings: in winter, in deep pots, with bottom heat slightly above the air temperature; they can take three months to root.
• Layering: in late winter and early spring it is often the most effective method; new plants bloom after two or three years.
• Seed: also possible.

Common problems

One symptom can have several causes: leaf drop can come from cold, but also from soggy mix that damages the roots. Look at the plant and its conditions before treating.

• No flowers: too little direct sun, too much water, pruning too often or too much nitrogen. On an established plant, pruning in late spring followed by a cooler spell can restart flowering.
• Winter leaf drop: night temperatures below 50 °F.
• Yellowing foliage: chlorosis in alkaline soil; also avoid very hard irrigation water.
• Pests: whiteflies, mealybugs, aphids and spider mites. The plant is generally free of disease.

Toxicity

No toxicity has been reported: bougainvillea does not appear among the plants listed as toxic to dogs and cats by veterinary references. Its sharp thorns, however, can injure the skin.