Winter heat protection sounds like a contradiction. Winter is cold, so why would plants need protection from heat? The honest answer is that winter heat protection is not about summer-style heat at all. It is about three different problems that all involve warmth in the wrong place or at the wrong time: freeze-thaw cycles, where a plant warms up in winter sun and then freezes again at night; drying winter sun and wind, which pull moisture out of leaves when frozen roots cannot replace it; and dry indoor heat, where central heating dries the air around houseplants until their leaves crisp and drop. This guide explains each problem honestly, and what to do about it.
If you came here expecting advice about shading plants from hot summer sun, that is a different job, and the summer guides cover it. In winter, the sun is low and weak, and the risk is not that plants will overheat — it is that they will warm up, start growing or lose water, and then be caught by frost. Understanding that difference is the key to everything in this guide.
Freeze-thaw: warmth that hurts
The most damaging winter pattern for many plants is not steady cold but repeated freezing and thawing. A plant that stays frozen is dormant and safe. A plant that thaws in winter sun, starts to move water and swell its buds, and then freezes again at night can be badly damaged, because ice forms in tissues that had started to become active. This is why a south-facing wall can be a dangerous place for a tender plant in winter: it warms up in the sun during the day, the plant starts to grow, and then the temperature drops at night and the new growth is killed. It is also why mulch matters: mulch steadies soil temperature, so the ground freezes once and stays frozen, or thaws gradually, rather than swinging between frozen and thawed every day. Our winter mulching guide covers mulch materials and depths, and the winter frost protection guide covers the other half of cold protection.
Evergreens are especially vulnerable to freeze-thaw, because they keep their leaves all winter. A broadleaf evergreen such as a rhododendron or a camellia that is warmed by winter sun loses water through its leaves, but its roots cannot replace that water because the soil is frozen — so the leaves dry out, brown and drop. This is winter burn, and it is caused by sun and wind, not by cold alone. The protection is shade and shelter: a screen of hessian or fleece on the sunny and windy side, a sheltered position out of the winter sun, and a mulch to keep the roots steady. Do not prune winter-burned evergreens in midwinter: wait until spring, when you can see what is alive, and prune back to healthy wood. Our growing roses guide covers a plant that can suffer the same drying in winter wind, and the zone 5 winter gardening guide shows how freeze-thaw works in a cold zone.
Drying winter sun and wind
Winter sun and wind dry plants out, and the damage is worst on evergreens, newly planted shrubs, and plants in exposed positions. The leaves lose water to sun and wind, the roots cannot replace it because the soil is cold or frozen, and the plant slowly desiccates. The signs are brown, crisp leaf edges, leaves that curl and drop, and, in severe cases, whole branches that die back. The protection is to reduce the drying: plant evergreens in a sheltered spot, out of the prevailing winter wind, and out of the strongest winter sun if the plant is vulnerable. A windbreak — a hedge, a fence, or a temporary screen of hessian — makes a real difference. Water evergreens before a cold, sunny spell if the soil is dry and not frozen, because a well-watered plant copes better than a dry one. Mulch around the base to hold moisture in the soil. And do not feed a plant that is suffering from winter drying: it needs water and shelter, not fertiliser, and feeding encourages soft growth that frost will damage.
Containers are especially vulnerable to drying wind, because a pot holds little soil and dries out fast, and a pot in a windy spot can dry out even in winter. Group pots together in a sheltered spot, check them on mild days, and water sparingly if the compost is dry. The watering calculator gives a starting point for how much water plants need in winter.
Dry indoor heat and houseplants
The third problem is indoors, and it is the one most gardeners actually meet. Central heating dries indoor air, and many houseplants suffer badly: leaf edges turn brown and crisp, leaves drop, new growth is small and distorted, and the plant looks unhappy even though it is warm and watered. The heating is not too hot for the plant — most houseplants like ordinary room temperatures. The problem is that hot, dry air pulls moisture out of the leaves faster than the roots can replace it, especially when the plant is growing slowly in short winter days and cannot take up water fast.
The fixes are practical. Keep plants away from radiators, hot air vents and fireplaces. Group plants together, so they create a more humid microclimate around each other. Stand pots on a tray of pebbles with water in the bottom, keeping the pot bases above the water so the roots do not sit in it. Mist occasionally, but do not rely on misting alone — it is a short-lived fix, and wet leaves in a cool room can encourage disease. A small humidifier in the room is the most reliable solution if you have many tropical plants. Water carefully: a plant in dry air needs water, but a plant in a cold room with wet soil will rot its roots, so check the soil before watering and let it drain. Our winter houseplant care guide covers the full winter routine for houseplants, and the humidity temperature checker — listed on the tools hub — will tell you whether your room suits your plants. If you are unsure about your indoor conditions, check your local extension service for advice.
Greenhouses: too hot and too cold
A greenhouse in winter can be both too cold at night and too hot during the day. On a sunny winter day, a closed greenhouse can heat up quickly, the plants inside start to grow, and then the temperature drops at night and the new growth is damaged — the same freeze-thaw problem, under glass. Ventilate a greenhouse on sunny days, even in winter, by opening the vents or the door a little, and close it up before night. Do not heat a greenhouse with an open flame or an unsuitable heater, and do not leave a heater running unattended without checking that it is safe. A cold frame has the same issue on a smaller scale: open the lid on mild, sunny days, and close it before night. Our greenhouse gardening guide covers greenhouse care through the year, and the winter frost protection guide covers the cold side of greenhouse care.
What not to do
Do not wrap plants in black plastic to keep them warm: black plastic absorbs sun, heats up during the day, and can cook the plant inside, then freezes at night. Use breathable fleece or hessian instead, which protects without overheating. Do not put a tender plant against a south-facing wall and assume it is safe — it may be warmer in the day and colder at night than a sheltered spot, and the freeze-thaw can do more damage than steady cold. Do not feed plants that are suffering from winter drying or freeze-thaw damage, and do not prune them in midwinter. Do not move a houseplant next to a radiator because it looks cold — the dry heat will do more harm than the cool room. And do not assume that because a plant is warm, it is happy: warmth without light and humidity is one of the worst combinations for a houseplant in winter.
Common mistakes
The most common mistake is thinking winter heat protection means shading plants from hot sun, and missing the real problems: freeze-thaw, drying wind, and dry indoor air. The second is wrapping plants in plastic, which overheats them by day and freezes them by night. The third is putting houseplants next to radiators. The fourth is watering a plant in dry indoor air without raising the humidity, so the leaves keep crisping even though the soil is wet. The fifth is feeding a plant that is stressed by winter drying. The sixth is leaving a greenhouse closed on a sunny winter day, so it overheats and then freezes at night. And the seventh is pruning freeze-damaged plants in midwinter, which exposes fresh cuts to the next frost. If you are unsure about protecting a particular plant in your area, check your local extension service for advice.
Frequently asked questions
What is winter heat protection?
In winter, it is not about summer heat. It is about protecting plants from freeze-thaw cycles, from drying winter sun and wind that pull moisture out of leaves when frozen roots cannot replace it, and from dry indoor heating that crisps houseplant leaves. Each problem has a different fix.
Why do evergreen leaves turn brown in winter?
Usually winter burn: sun and wind dry the leaves out while the roots cannot take up water from frozen or cold soil. Shelter the plant from wind and strong winter sun, water it before a cold sunny spell if the soil is not frozen, and mulch around the base.
Is my radiator harming my houseplants?
It can be. Central heating dries the air, and hot, dry air pulls moisture from leaves faster than the roots can replace it. Keep plants away from radiators and vents, group them together, use a pebble tray, and consider a humidifier.
Should I wrap plants in plastic for winter?
No. Plastic does not breathe, it heats up in winter sun and can cook the plant, and it can freeze to leaves. Use breathable horticultural fleece or hessian instead, and remove covers during the day so plants get light and air.
Why does my greenhouse get too hot in winter?
On a sunny winter day, a closed greenhouse heats up quickly, plants start to grow, and then the temperature drops at night and the new growth is damaged. Ventilate on sunny days, even in winter, and close the greenhouse up before night.