How to Overwinter Mandevilla and Coleus in Ontario

Every year at the fall changeover I get the same question, usually while I am standing in someone’s driveway with an armful of their summer planting. What do I do with all of this? It looks fine. Do I really just throw it out?

Some of it, yes. But not the mandevilla, and not the coleus. Those two are the ones worth carrying through the winter, and neither one is difficult. The mandevilla I put away in the dark and forget about until March. The coleus I take cuttings from and keep on a windowsill. Both cost me about fifteen minutes in October and save me buying the same plants again in May.

Here is exactly how I do it, and how to tell which of your plants are worth the trouble.

The short version

• Act on temperature, not on frost. Both plants are done once nights sit near 10°C. In the GTA that is usually late September, well before the first frost.
• Mandevilla: cut it back hard to about 12 inches, put it somewhere cool and dark, water it barely, bring it out in March.
• Coleus: take cuttings rather than dragging the whole plant inside. They root in a glass of water on a windowsill.
• Do not bother with petunias, calibrachoa or anything else that was exhausted by August. Saving a tired plant gets you a tired plant.

When to lift them, if you are in southern Ontario

Most people wait for frost. That is too late, and it is the single most common reason this fails.

Mandevilla and coleus are both tropicals, hardy only in the warmest parts of the continent. They do not need ice to be damaged. Nights in the low single digits are enough to set them back, and by the time you see actual frost damage the plant has already spent a week or two being quietly injured.

For Toronto, the record puts a real risk of frost from around 10 October, with a 50% chance of a light freeze by 28 October and near certainty by early November. Useful to know, but treat it as your outside limit, not your plan. The night-time temperature is the trigger. Once the forecast shows a run of nights near 10°C, it is time.

In practice that means late September through the first week of October for most of the GTA, which lines up neatly with the fall changeover anyway. If I am already at a house swapping the summer planting out for fall planters, the mandevilla comes out the same afternoon.

Mandevilla: two ways, and only one of them is easy

Mandevilla goes dormant from roughly October through to March or April whether you cooperate or not. That is worth sitting with for a second, because it decides everything else. You are not choosing whether the plant slows down. You are only choosing whether you fight it.

Option one: put it to sleep, which is what I do

Cut it back hard. Not a tidy trim, a real cut, down to about 12 inches. I know how that feels the first time, particularly on a plant that is still flowering. Do it anyway. Every leaf and every bloom on that plant is about to drop regardless, and all of them are drawing on energy that should be going into the roots.

Then move the pot somewhere cool and dark and leave it alone. Mine goes into the crawl space. A basement corner, an unheated but frost-free garage, a cold cellar, all fine. Around 10°C is the target and the only hard rule is that it must not freeze.

Water almost not at all. The soil should be slightly damp and no more. A dormant plant with no leaves is barely drinking, and the fastest way to lose one over winter is to keep watering it as though it were still growing. Check it once a month. If it has gone bone dry, give it a little. Otherwise close the door.

This is the whole method in the video below.

Option two: keep it growing indoors

You can keep a mandevilla in active growth through the winter. Cut it back by about half, put it in the brightest window you have, keep it somewhere that stays in the high teens to low twenties, and water when the top of the soil dries. Hold off on fertiliser until February, then prune again and feed monthly to push it toward spring.

I want to be straight about what this actually looks like. It will not flower the way it did in July. It will drop leaves. It will get leggy reaching for light that a Canadian window simply does not provide in January. You are keeping a plant alive, not keeping a display.

There is also the practical question nobody mentions in the articles. A mature mandevilla off a front entrance is enormous. Finding a bright, warm, draught-free spot for something that size, for five months, in a house you also live in, is a genuine ask.

Which one to choose

Pick dormant storage if the plant is large, if you do not have a south-facing window going spare, or if you want to think about it exactly once between now and spring. That is most people, and it is why it is the method I use and teach.

Pick the houseplant route if it is a small plant, you genuinely like having something green indoors through the winter, and you have the light to give it. Both work. One is far less work.

Coleus: take cuttings, not the plant

Coleus is the other one I always save, because the good varieties are the ones that vanish from the garden centre first and the colour combinations I build planters around are not always there again next year.

You can bring the whole plant in. If it was in the ground rather than a pot, repot it in fresh potting soil first so you are not importing whatever has been living in the garden bed. But by late September a coleus that has been performing since May is usually woody at the base and thin on top, and what you are rescuing is a plant past its best.

Cuttings are easier and give you a better plant. Take 4 to 6 inches off healthy stems, strip the lower leaves, and stand them in a glass of water on a bright sill. Roots appear within a couple of weeks. Once the roots are past an inch, pot them up. By May you have several young vigorous plants instead of one tired old one, from a variety you already know you like.

Keep them out of hot and cold draughts, which means not over a radiator and not beside the front door.

What else is worth the effort

The rule I use is simple. Save it if it was expensive, if it is large enough that replacing it costs real money, or if it is a variety you will struggle to find again. The dormant storage method above works for most of the big tender tropicals that anchor a planter, the red banana included.

Do not save the annuals that were always going to be annuals. Petunias, calibrachoa, anything that had already gone leggy and stopped flowering by mid August. They were bred to give you one spectacular season and they gave it. Composting them is not a failure.

The five mistakes I see every year

1. Waiting for frost. By then the damage is done. Watch for nights near 10°C instead.
2. Not cutting back hard enough. A half-hearted trim leaves the plant carrying foliage it cannot support in the dark.
3. Watering it like a houseplant. Dormant plants rot far more often than they dry out.
4. Storing somewhere that freezes. An attached garage usually holds. A detached one in February usually does not.
5. Forgetting it entirely. One check a month is all it needs, but it does need that one.

Waking it up in spring

Around March, bring the mandevilla up out of the dark and put it in front of the sunniest window you have. South facing is ideal, but any window will do the job. Start watering normally again and it will push new growth within a few weeks.

Once the nights are reliably warm, which in the GTA means late May rather than the first nice weekend in April, it goes back outside. And you are starting the season with a mature, established plant instead of a small one in a nursery pot, which is exactly the difference between a planter that looks full in June and one that is still filling in come August.

If you would rather someone else made these calls, timing included, that is what the four season plan is for. And if you are working out what goes in the planter once the summer comes out, the complete fall planter guide covers the rest of the changeover.