Chapter 78 Bougainvillea glabra, B. spectabilis

78.1 Lesser bougainvillea, greater bougainvillea

An enormous Bougainvillea in the collection of the Brooklyn Botanical Garden. This tree falls squarely in the Imperial size class for bonsai. Link to original image

78.2 Soil: Rich/Tropical Mix

Ratio: 4 parts bark, 1 part coir, 1 part grit

Add-ins: dolomitic limestone (~3 lbs/yd), Tree-Tone (15 lbs/yd)

pH: Optimum is 6.0 (well below neutral; limestone adjusted)

Moisture: moisture retaining

78.3 Light

Needs bright light indoors, and does best in mostly to full sun.

78.4 Cultivation Notes

78.4.1 Potting

Bougainvillea is very fussy about having its roots disturbed. This is aggravated by their habit of not forming a cohesive root mass. They do not like frequent repotting, and actually do better when the roots are crowded, though they are harder to keep well watered in this state. Repot gently and remove as few roots as possible.

Bougainvillea need well-drained yet moisture retentive soil. This is why I use coconut coir in the soil mix, because it meets both the drainaage and moisture requirements. In the ground they are drought-resistant, but in pots I find they are less tolerant of inadequate water.

In practice, I do not make a separate batch of soil for my bougainvilleas. Instead I start with my regular soil mix of 3 parts bark/1 part grit plus lime. This will be around pH 6.5. I combine 2 parts of the soil mix with 1 part bark, and 1 part coir, but no additional limestone. This, raises the organic fraction, increases water retention without sacrificing drainage, and lowers the pH.

78.4.2 Pruning

Watch for dead wood year round, and remove it as it appears. Hard pruning should be done shortly after the bougainvillea has flowered, or during dormancy. Finger pinch the soft, growing tips of young plant stems to encourage branching and thicker growth. Cut longer shoots off at the woodier main branches. Shoots tend to come off at odd angles; once they start extending, they are difficult to re-direct in another direction. Instead of trying to bend the green shoots, clip them back and train a side shoot in the right direction.

Bougainvillea tolerate very aggressive pruning, which makes it easier to develop tight masses of foliage and flowers like those shown here. Link to original image

78.4.3 Feeding

Fertilize bougainvillea every month in spring and early summer with a balanced, all-purpose liquid fertilizer at half the normal dosage.

78.4.4 Pests & Problems

Indoors, mine get aphids and mealybugs sometimes, but these can be controlled with insecticidal soap. Moving the trees back outdoors almost always kills the pests.

78.4.5 Winter Storage

Bougainvilleas cannot withstand frost and freezing weather. Bring them indoors once night-time temperatures drop below 40^oF.

78.5 Propagation Notes

Green tip cuttings root easily. Dip them in rooting hormone, sink the cut ends in rooting mix, and keep them humid. Many of the cuttings will root within 6-8 weeks.

78.6 Artistic & Styling Notes

They do well in slanting or semi-cascade styles with taller, deeper containers that do not need repotting as frequently.

Bougainvillea does best with benign neglect, not babying. They prefer full sun and definitely like to be outside all summer. They love our summer humidity.

They need full sun to set flower buds and will not set buds without it. Mine stay out all summer, and usually bloom within a couple weeks of coming indoors in early November.

Failure to bloom (and leggy growth) usually means it is not getting enough direct light. Excess water also can short circuit flower formation. They bloom on newer growth, so pruning too close to blooming tine can limit flowering. Finally, too much nitrogen encourages them to produce leaves instead of blooms.

78.7 Additional Information

78.7.1 Natural History

This entire genus is made up of thorny tropical ornamental vines, bushes, or trees. It is native to South America from Brazil west to Peru and south to southern Argentina. What we think of as flowers are actually bracts (modified leaves) similar to the poinsettias. The actual flowers are the 3 simple waxy-colored tubes in the center of the bracts.

They have been introduced or naturalized in tropical areas worldwide, including Florida, California, Texas, and Asia.

78.7.1.1 Cultivation

There are 4- 18 species as well as cultivated hybrids. Bougainvillea glabra is the most common species used for bonsai. B. spectabilis is less common, and has hairy or velvety undersides to the leaves.

More than 200 cultivars have been selected, almost all of which are hybrids of three species. Mutations often occur in growing tips, producing new colors and morphs that can be propagated clonally by tip cuttings.