Originally from South America, bougainvillea is now widely grown wherever the climate permits. While famous for its abundant, showy flowers, the colorful parts of the plant are, in fact, bracts or modified leaves. The bougainvillea flower itself is small, white and tubular. Spontaneous hybridization between the three species in cultivation has given rise to a large variety of cultivars, with red, yellow, white, purple and orange bracts and even variegated leaves.
Bougainvilleas are suitable for outdoor cultivation in USDA zones 9 and above but will be killed off down to the ground by even light frost. Large and established plants will recover from frost damage and send up new shoots in the spring. Choose Bougainvillea glabra if you live in areas prone to frost as it is the hardiest species. Bougainvillea is not a fussy plant and will grow well in almost any soil type provided it is well-drained. The root system is very fine and sensitive to water logging. Plant your bougainvillea in full sunshine after the last frost.
Water your plant freely in the summer months but allow the surface of the soil around the plant to dry out completely between waterings. Allowing the leaves of a bougainvillea to wilt slightly before watering will encourage flowering. During the short dormant period in the winter, the plant only requires watering when the soil surface is dry. Do not over water a bougainvillea during the winter months as the roots are vulnerable to rotting.
Fertilize your plant every two weeks with a liquid fertilizer at half the recommended strength during the growing season. Choose a fertilizer that is low in nitrogen, to encourage flowering over leaf production, and is enriched with trace elements such as iron. If you see any yellowing of your plants leaves, spray with a foliar spray containing chelated iron. Bougainvilleas thrive with a constant supply of nutrients and over fertilizing can damage the root system and suppress growth.
Training and Pruning
Left to grow naturally bougainvillea can send out stems up to 30 feet long and will suffocate surrounding plants that are less vigorous. It can be trained up a pergola or along wires on a wall or simply left to drape over a high wall. Many cultivars have sharp thorns on the older stems and should be trained or pruned away from paths and doorways. Bougainvillea plants can also be pruned into a free standing shrub up to 6 feet high and make excellent hedges. Pruning back a bougainvillea plant encourages flowering as the flowers come on new growth.
Bougainvillea is generally hardy and resistant to most garden pests. Check your plant regularly for signs of aphids, scale insect and mealy bugs. Treat these with an organic pyrethrin based insecticide as soon as they appear. Leaf roller caterpillars are sometimes a threat but can be picked off at night or treated with an insecticide. If your bougainvillea has fine white webbing and mottled yellow markings on the leaves, it probably has spider mites. Increase the humidity around the plant by misting or spraying it twice a day. If the problem does not clear up use a miticide spray.
Cultivated bougainvilleas very rarely set seed and are propagated by cuttings taken during the summer. Soft tips cuttings about 6 inches long will root in damp sand or soil free compost provided they are kept warm and humid. Woody cuttings about a foot long will root in soil free compost if planted with one third of the cutting under ground.