Overwintering Hibiscus Indoors: Bringing It In and Keeping It Alive

Know which hibiscus you have before you leave it out

The word hibiscus covers two very different garden plants, and confusing them is how people lose one. The tropical hibiscus, the glossy-leaved evergreen usually grown in a pot with large flowers over a long season, is not frost hardy and will be killed outright by a hard freeze. It has to come indoors in any climate with real winter.

The hardy kinds, which drop their leaves in autumn and are planted in the ground, are a separate group and stay outside. If your plant is evergreen, glossy-leaved and living in a container, treat everything here as applying to it.

The tropical plant stops growing well below about 50F (10C) and starts suffering below about 45F (7C). Brief exposure to the low forties Fahrenheit (around 5C) yellows leaves and sheds buds without killing the plant; an actual frost kills the top growth and usually the whole plant in a pot, since the roots freeze too.

Plan the move for well before the first cold night rather than in reaction to a forecast. A plant brought in calmly in mild weather adjusts far better than one rushed indoors after a chill.

Bringing it in without shedding everything

The move indoors is a large change in light, temperature and air movement all at once, and the plant answers it by dropping leaves and buds. You cannot avoid this entirely but you can reduce it a great deal by making the change gradual and by getting the pests off first.

Give it a week in a sheltered, shadier spot outdoors before it comes in, which begins the light adjustment while the temperature is still comfortable. Then bring it into the brightest available position rather than wherever there happens to be space, because a plant that lands in a dim corner after full sun will strip itself bare.

Wash it down thoroughly before it crosses the threshold. Take it to a hose or shower and spray the undersides of every leaf, then look carefully at leaf joints and shoot tips for aphids, whitefly and mealybugs. Anything that survives the move will breed all winter in warm still air with nothing to check it.

Once it is in place, leave it there. Turning it, moving it out of the way for a week, or shifting it to a different window all cause further leaf and bud loss. A hibiscus rewards being ignored in winter more than almost any other flowering plant.

1. Prune lightly, if at all Take off only what is dead, damaged or in the way of getting the plant through a doorway. Real pruning belongs in spring, and cutting hard now produces soft growth that cannot cope with low light.
2. Wash and inspect for pests Spray the undersides of the leaves with plain water, then check tips and leaf joints. Treat anything you find before the plant goes in, and check again a week after it is indoors.
3. Move it in stages A week in a shadier sheltered spot outdoors, then indoors. This halves the light shock and noticeably reduces how many leaves the plant drops in the following fortnight.
4. Choose the brightest cool position A window with good direct light in a room that stays around 55 to 65F (13 to 18C) is ideal. Keep it well clear of radiators, heating vents and the draft of an outside door.
5. Cut the watering right back Switch immediately to watering only when the top inch (2.5 cm) of compost is dry. The plant is barely growing and its water use has fallen to a fraction of what it was outdoors.

Winter watering is where plants are lost

Far more overwintered hibiscus die from being watered on a summer schedule in a cool room than from anything else. Growth has almost stopped, the days are short, evaporation is slow, and compost that dried out in a day in midsummer can stay damp for a fortnight in the depths of winter. Watering into that leaves roots sitting in cold wet compost, and they rot.

Check with a finger rather than a routine. Push it an inch (2.5 cm) into the compost; if there is any moisture, leave it. When it is dry at that depth, water moderately and let all the surplus drain away. Never leave the pot standing in water in winter.

The confusing part is that overwatering and underwatering look similar. Both give you yellowing leaves that drop. The difference is in the compost and the stem: a plant that is too wet has permanently damp compost, a sour smell to the pot and often soft dark tissue at the base, while a plant that is too dry has compost shrunk from the sides of the pot and leaves that crisp at the edges before they fall.

Some leaf loss through winter is normal even when you get the watering right. A plant that ends the winter thinner than it started, with firm stems and live buds, has come through fine and will refurnish itself quickly in spring.

If a plant does lose all its leaves, do not throw it away and do not water it more. Scratch the bark with a thumbnail: green underneath means the stem is alive. Keep it barely moist and cool, and it will very often shoot again once the light returns in spring.

Coming back out, and what to record

In spring, wait for nights to be reliably above about 50F (10C) before the plant goes back out, and harden it off properly. Winter leaves scorch in full sun within a couple of days, so give it a week in shade, then a week in morning sun only, then its full position. This is the same process as autumn in reverse and matters just as much.

Do the pruning and any repotting before it goes out, as the plant starts into growth. That way the disturbance happens indoors in controlled conditions and the regrowth begins right as the outdoor season starts.

Keep four dates and the plant becomes far easier to manage year on year: when it came in, when it went back out, roughly how much leaf it lost over winter, and where in the house it stood. After two winters you will know which window works and how early you can safely move it, which is worth more than any general advice.

Note the pests too. Whitefly indoors is almost always traceable to the week the plant came in, and a note of that date tells you exactly when to start weekly inspections next year.