BOUGAINVILLEA blooms when day length is short from early winter into late spring. After blooming stops the plants should be pruned back to improve form and encourage new growth, which will re-flower in the shorter days of autumn. When it is in active growth this plant must have frequent and through watering. If it dries out it will drop leaves and may flower prematurely (and poorly).
Mays Greenhouse ©2010
If you wish it to bloom during summer subjecting the plant to periodic water stress can trigger bud formation. Over-doing this can cause defoliation. Careful pinching back during the growing season will keep the plant small enough to be manageable as a pot plant or hanging basket. Left untrimmed it can become rather large and vine-like in even one summer. If this is desirable be sure to provide some sort of trellis and train the new growth to it while it is still tender and flexible.
A general purpose soluble fertilize is suitable for feeding. If pale foliage with darker green veins develops it can usually be corrected with an application of Epsom Salts, (Magnesium sulphate) at the rate of 1 Tbsp. per gallon of water. This is a plant that does well at usual house temperatures, 70-80 degree days, 60 to 65 degree nights. Many people summer these plants outdoors, returning them to the house when night temperatures drop to 60 degrees. Indoors provide strong natural light.
Flower formation is linked to day length. To encourage autumn blooming provide nights of 14 hours length, and 10 hour days. This may require placing the plant in an unused room where artificial lighting will not be used, or, if no such place is available, place the plant in a closet or cover it at the proper time each day until buds begin to form. During the autumn bud initiation period, feed with a high nitrogen fertilizer. When transplanting or re-potting take care not to disturb existing roots.