Overwintering Bougainvillea: Cold, Leaf Drop and Watering

What it can and cannot take

Bougainvillea comes from a warm, frost-free climate and it shows. Below about 41F (5C) growth stops completely. At around freezing the soft growth is damaged. A hard frost of 27F (minus 3C) or lower kills stems outright, and a prolonged freeze kills the plant to the roots and usually beyond.

In practice this means that outside genuinely frost-free areas the plant has to come under cover for the cool months. This is a large part of why it is grown in containers even in places where it would technically survive outdoors, since a pot can be moved and a plant in the ground cannot.

The good news is that it does not need much. It is not trying to grow, and a bright, frost-free space at 45 to 55F (7 to 13C) suits it perfectly. An unheated conservatory, a porch, a cool spare room or a frost-free greenhouse are all fine. It does not need a warm living room, and in fact a warm room with poor light is one of the worse options because it encourages weak growth the plant cannot support.

Cold roots are more dangerous than cold air. A pot on a stone floor in an unheated space can be several degrees colder than the room, and cold wet compost is the combination that kills. Raise the pot onto a wooden board or a slab of insulation.

Leaf drop is not an emergency

When you move a bougainvillea indoors it will drop leaves, often most of them, within a couple of weeks. Every year people assume the plant is dying and start watering and feeding to revive it, which is the one thing guaranteed to finish it off.

The shed is a response to the drop in light and temperature and it is exactly what the plant does at the end of the dry season in the wild. A leafless bougainvillea in winter with firm, green-barked stems is a healthy plant that is resting. Scratch a stem lightly with a thumbnail; green underneath means it is alive, and that is all you need to know.

The corresponding fact is that a leafless plant uses almost no water. Its transpiration is close to zero and compost stays wet for weeks. Watering to a summer routine at this point drowns the roots at precisely the time they are least able to cope.

Expect the display to go with the leaves too. Any bracts still on the plant when it comes inside will fade and drop quickly, because they are modified leaves and they leave with the rest.

Do not prune a plant that has just shed its leaves. Wait until late winter when you can see which stems have survived. Cutting in early winter removes wood the plant may still need and opens fresh wounds when nothing is growing to heal them.

Winter routine

The whole point of the winter routine is that there barely is one. Your job is to keep the plant cool, bright and dry and otherwise to leave it alone until conditions turn.

1. Move it before the first cold nights Bring the pot in when night temperatures start dropping towards 45F (7C), rather than waiting for a frost warning. A gradual move is less of a shock than a rescue during a cold snap, and it gives you time to check for pests first.
2. Inspect and clean it on the way in Check leaf undersides and stem joints for mealybug and spider mite, and deal with anything you find before it goes into a warm, still space where the population will multiply all winter. Wear thick gloves.
3. Give it the brightest cool spot you have A south-facing window in an unheated room is ideal. Light matters more than warmth. Keep it away from radiators and away from drafts from an outside door, both of which cause more damage than steady cool.
4. Cut watering right back Water only when the compost is dry two inches (5 cm) down, which through the cool months may mean once every three or four weeks. Give a small amount when you do, enough to moisten rather than to soak, and empty any saucer immediately.
5. Stop feeding completely No fertilizer at all until growth restarts in spring. Feeding a dormant plant does nothing useful and salts build up in compost that is not being flushed through by regular watering.
6. Prune in late winter, then wake it Once the worst cold has passed, cut out dead and weak stems and shorten the main framework. Then increase water slightly and move it somewhere warmer to bring it into growth.

Bringing it out again

Growth restarts when temperatures are reliably above 59F (15C) and light lengthens. New leaves appear from bare wood, often lower down the stems than you expect, and that is the signal to increase watering and begin feeding again.

Harden it off before it goes back outside. Leaves that formed in low winter light scorch badly in direct sun, and a plant taken straight from a windowsill to a sunny patio can lose the lot in an afternoon. Give it a week or two in dappled or morning-only sun, increasing gradually.

Do not put it out until nights are safely above 50F (10C). It is worth being late; a plant that goes out too early and gets checked by a cold night will lose weeks of growth and the first flush of color with it.

The first flush of bracts usually follows six to ten weeks after growth restarts, so the timing of when you wake the plant sets the timing of the display. Once it is out, in sun, and growing, start the dry cycle again and stop worrying about it.

What winter notes are worth keeping

Overwintering is where most bougainvillea are lost, and the mistakes repeat annually because nobody remembers the detail from last time.

Record every winter watering with its date. Reading back a list of four dates across a whole cool season is reassuring; reading back twelve tells you immediately why the plant struggled. Note the coldest temperature the plant actually experienced where it stood, rather than the outdoor forecast, since a minimum thermometer next to the pot often reveals a much colder spot than you assumed.

Write down the date you moved it in and the date you moved it out, and how much leaf it dropped. Over two or three years that gives you a reliable window for your own conditions. Note the date growth restarted, too, because it lets you count forward to when color should appear and judge whether the plant is behaving normally.