First let’s understand the plant. Bougainvilleas are native to tropical and subtropical South America. They love full sun, moderate to regular water, and are frost-tender. They also like good drainage and rich soil.
“Barbara Karst”, “San Diego Red”, “Scarlet Ohara“, “James Walker”, “Purple Queen” and B. brasiliensis can be very successful here in the Bay Area. In areas where there are regular frosts, they will need winter protection.
Tall growing bougainvilleas grow fast and can reach 15 to 30, depending on the variety. They need to be planted near a protected wall or the warmest spot in the garden. They need to be tied to some kind of support, so remove the grower’s stakes after planting and tie the stems to a trellis or fence. Since they are frost-tender, watch the weather in the winter and water them the day before the temperature drops. Bush-type bougainvilleas grown in pots can be moved to a protected spot, but don’t let them dry out completely in the winter. bougainvilleas can’t tolerate wet feet so please don’t use a saucer under their pots. Prepare the planting hole by digging a space the same depth as the can and twice as wide. Fill the hole with water and let it drain. Then, ever so gently, ease the root ball out of the pot and place in the hole. Another technique is to place the can in the planting hole, and cut it away from the root ball. (bougainvilleas roots are notoriously sensitive and don’t respond well to the usual loosening practice). Backfill with amended soil mixed with SureStart, firm in so the root ball makes good contact with the existing soil and water in deeply.
Bougainvilleas can be drought-resistant after they have become established, but until then give them regular deep watering in spring, and then cut back to less frequent ,but still deep water during the bloom period.
In early spring apply fertilizers that are high in Phosphorus, iron and other micronutrients. bougainvilleas are not heavy feeders, so an organic or slow-release fertilizer is best. Tip-pruning will encourage fullness but remember bougainvilleas bloom on new wood. Vigorous pruning in the spring, after frost danger is over, may slow down your bloom season. If this was the case for your bougainvilleas this year you may wish to prune after the bloom season is finished. Keep in mind the finished bloom and inevitable cleanup. Do you want to sweep/rake up old blossoms from the patio or front steps, or can you leave the blossoms to decompose on the soil if planted further back in the garden?