Water a newly planted bougainvillea frequently to keep the soil moist. Once the plant is established, it blooms best if the soil is a little on the dry side. Water the plant until liquid drips through the drainage hole, then don’t water again until the potting mixture feels slightly dry. However, don’t allow the soil to become completely dry because a water-stressed plant won’t bloom. Water the plant immediately if it looks wilted. Bougainvillea is a heavy feeder and requires regular fertilization to produce blooms throughout the growing season. You can use a water-soluble fertilizer mixed at half strength every seven to 14 days, or apply a slow-release fertilizer in spring and midsummer. Bougainvillea blooms on new growth. This means you can prune the plant as needed to maintain the desired size. The ideal time to trim the plant is immediately following a flush of blooms.