Question: I have a beautiful bougainvillea that has bloomed all summer. I was told that I could keep it indoors in the winter, but how?
Answer: The bougainvillea (Bougainvillea spp.) is a spiny climbing subtropical shrub that can bloom on and on for months, even all year long under very good conditions. There are more than 300 cultivars with different colors of bracts, most of which are complex hybrids between different species. You’ll see giant specimens covering entire walls in Mediterranean and tropical climates, but also potted bougainvilleas of a much smaller size (thanks to judicious pruning) sold in pots and baskets as a summer annual in colder areas.
The bougainvillea was named in honor of Count Louis-Antoine de Bougainville, an 18th century French aristocrat, navigator and explorer.
What a bougainvillea likes is full tropical sun, moderate watering (unlike most plants, it does better if you keep it on the dry side than evenly moist) and regular fertilization during its growing period. In regions with mild winters (zones 9 to 11), where it can be planted outdoors, that can sometimes be all year, but in more Mediterranean climates it will go semi-dormant and stop blooming over the winter. In temperate climates, you either have to grow it as an annual and let it die in the fall, or shelter it indoors over the winter … and keeping it alive it indoors during the dark days of winter is the subject of this article.
The true “flowers” of the bougainvillea are small, fairly ephemeral white or pale yellow trumpets surrounded by three papery bracts (double bougainvilleas have more bracts). It’s these bracts in red, purple, yellow, orange and white—and that last for months!— that give the plant its festive appearance.
Keeping It Alive
Make sure you bring your bougainvillea indoors before frost hits. True enough, you’ll read that it’s able to tolerate some frost, but that’s when it’s growing in the ground … and even then, the damage can be severe. In pots, where frost can penetrate right through the root ball in no time, a serious cold snap can kill it outright.
There are two ways to keep a bougainvillea alive indoors over the winter: keeping it growing as a houseplant or forcing it into dormancy.
1. As a Houseplant
Place the plant in the sunniest spot possible, preferably in front of a large south-facing window or, better yet, in a moderately heated greenhouse or veranda with light coming from several sides. Even under these conditions, the plant will probably lose many of its leaves when you bring it in, as lighting indoors is always less than outdoors.
Things will only get worse as autumn gives way to winter and days become shorter and darker. In temperate regions, winter light is rarely sufficient for its taste. Good atmospheric moisture may help the plant to retain a few more leaves though.
Ideally, you’d lower the temperature as well to 45 °F or 50 °F (8 °C or 10 °C), but that’s not always possible in many homes. Fortunately, it will put up with room temperatures if it has too.
Your goal during the fall and winter is just to keep your bougainvillea alive, not to stimulate growth, so water very modestly, letting the soil dry out considerably before watering again. Nor should you fertilize in fall or winter: that will only stimulate weak growth you’ll have to prune off later.
2. Force It Into Dormancy
Dormancy is not a normal state for bougainvilleas. In the wild, they do best where they can grow at least a bit at all times. Still, they’ll adapt to it if necessary.
To initiate dormancy, place the plant in a cool basement, a heated garage or any other cold but frost-free spot. No light is needed: the plant will be dormant, after all. Water only enough so that the root ball doesn’t dry out completely, perhaps once or twice a month. The plant will lose all its leaves, but that doesn’t mean it’s dead.
Back to Life in Spring
With the return of longer days in March, it’s time to wake your bougainvillea up. If possible, place the plant in a sunny room and start giving it better care, especially more frequent waterings. Start fertilizing it too (any fertilizer will do), lightly at first, at about one eighth of the recommend rate, then more as it puts on more growth. The idea at this point is to give it a head start on summer.
This is also the time for a bit of pruning. Since bougainvilleas bloom on new wood, you can cut them back quite severely and that should stimulate the growth of more branches and therefore more bloom in the months to come. Besides, who has the space to allow a potted plant to produce branches 10 feet (3 m) long? However, the downside to pruning is that it will also delay blooming. A good compromise is to cut the branches back by about a third. (Note too that, during the summer months, you should also prune back any stems that are getting too long.)
If you want to repot, spring is also the right season. Note that bougainvilleas bloom best when they’re a bit underpotted … but they’re fast-growing plants: after 2 or 3 years, you’ll have no choice but to repot it.
A Summer Outdoors
As soon as the risk of frost is gone, gradually acclimatize the plant to outdoor conditions. A site in full sun is ideal. And remember to water and fertilize regularly.
Remember that bougainvilleas really aren’t good houseplants, that you only bring them indoors to keep them alive until the following summer. It’s outdoors under the intense summer sun that bougainvilleas truly strut their stuff! So be prepared to accept a rather discouraging winter appearance as the price to pay for beautiful summer blooms!