Bougainvilleas are the most popular and spectacular of all the tropical flowering climbers. This South American native was named after Louis Antoine de Bouganville, the great French explorer, navigator, scientist, and author.
In tropical latitudes they flower year-round with peak flowering occurring during the drier, sunnier times of the year. In New Zealand, most bougainvilleas begin to flower during late spring and continue right through the warm weather with peak flowering around December through February.
This peak can vary being dependent on seasonal variations and where and how the plant is grown and situated to the sun. Bougainvilleas are sun lovers and can never get enough sunlight and warmth. The most important secret to their success is to plant them in the hottest exposure possible.
The ideal is to place them where the entire vine will be exposed to the sun all day including the rootrun. They are also highly drought resistant and often flower well when established in a dry spot even when it is partly shaded. But for the most spectacular blooms plant against a very sunny wall in a rich soil that drains perfectly.
Planting on the north or sunny side of a fence, shed, old tree trunk, or trellis often gets good results provided the site is not too exposed to cold winds, frosts and freezing which can set them back. Failure of flowering usually is associated with too much shade or soils that remain too wet.
Over feeding with fertilisers high in nitrogen will lead to rampant growth at the expense of flowering. The other factor is low soil temperature. Being tropical climbers they demand a very warm soil for good plant health and superior flowering. This is especially true of the lovely tropical hybrids.
To raise the soil temperature, it is often wise to grow bougainvilleas within a square of black plastic or weed mat. The black coloured plastic is an excellent method of raising the soil temperature to a sufficient level. Bougainvillea flowers are actually quite small, creamy white trumpets partially hidden within the brilliantly colourful bracts (modified leaves) that often smother the evergreen vines.
These bracts occur at the ends of newly grown canes and from new growth side shoots sprouting from older, mature wood. For this reason it is best to prune bougainvilleas directly after flowering. This pruning can be quite severe without damaging the vines. They are often pruned as topiaries and as ornamentals in containers. Shrubby variety Temple Fire is often pruned into an ornamental street tree in Brazil.
They also espalier easily on walls and fences. Some like variegated Tropic Rainbow and Sandersonii Variegata make interesting specimens in hanging baskets. Magnifica trailii (purple, lavender, mauve shades) is the hardiest and most rampant. Scarlet O'Hara is flaming crimson, vigorous and a brilliant bloomer for dry sites.
Carmencita is an excellent carmine red double. Hawaiian Orange, White and Yellow are great exotic tropical colours for really hot spots.