Houseplant Cold Damage: The Kind You Cannot See
Houseplant cold damage starts well above freezing, and the most common injury leaves no mark at all. What the chilling experiments actually found.
Houseplant Cold Damage: The Kind You Cannot See
Houseplant cold damage does not require frost, or even anything a person would call cold. A Chinese evergreen held at 55°F for a single night came out with damage on a third of its leaves, and a peace lily held at 52°F came out looking perfectly fine and was measurably smaller six weeks later.
The second result is the one worth carrying around. Most cold injury indoors is invisible at the time, shows up as a plant that simply stops doing well, and gets treated as a feeding problem.
What temperature is too cold for houseplants?
Lower than the comfortable range, and much higher than most people assume.
University of Maryland Extension gives the target: foliage indoor plants grow best between 70° and 80°F during the day and from 60° to 68°F at night. Missouri Extension marks the point where real trouble starts, noting that Some tropical foliage plants can be injured by temperatures below 40 degrees F.
Between those two figures sits a wide band that feels fine to a person and is not fine to a tropical plant, and it has a name. Clemson defines the category: Chilling injury can occur to many tropical plants although temperatures do not drop below 32 °F.
Freezing is a separate and more obvious event. Chilling is what happens in the 40s and 50s, and it is the one that actually occurs in a heated apartment.
What a single cold night does
University of Florida's foliage plant program ran the experiment directly rather than reasoning from theory, which is rare in this literature.
Twelve Chinese evergreen cultivars, grown to marketable size, were put in walk-in coolers at 35°F, 45°F and 55°F for 24 hours, then watched daily for ten days. Dark and greasy patches appeared between midvein and leaf margin on the upper surface of leaves two days after chilling at 35°F, 45°F, or 55°F.
The cultivar numbers are the part that should change where you put a plant. Silver Queen, which UF calls one of the most popular cultivars in the foliage plant industry, was extremely sensitive to chilling, with 30%, 38%, and 68% of leaves injured at 55°F, 45°F, and 35°F for 24 hours.
Thirty percent of the leaves, from one night at 55°F. That is around 13°C. It is a mild autumn evening, and it is well within what an apartment windowsill reaches once the heating goes off overnight.
Which leaves take it is also useful, because it inverts what people expect. UF found that Mature and old leaves appeared to be much more sensitive to chilling than young leaves, with the split coming out stark: mature leaf injury ranged from 45% to 100% and old leaves from 14% to 53%, but young leaf injury was only 0% to 6% depending on cultivar.
So a cold-damaged plant loses its established leaves and keeps its new ones, which reads from across the room like a plant that is fine and growing.
The houseplant cold damage that leaves no mark
The companion study on peace lilies is the one that changes how you read a plant in March.
UF chilled eight Spathiphyllum cultivars at 52°F for five or ten days, then compared them against controls grown at normal greenhouse temperatures. On inspection there was nothing to find: No visual injury occurred in plants exposed to 52°F.
Then they measured. Growth index, defined on the page as the average of two canopy widths multiplied by plant height, was recorded 45 days later, and they were found to be smaller than those of the controls.
Running their published table: all eight cultivars came out smaller than their controls, after both the five-day and the ten-day exposure. The shortfall after five days ranges from about 10 percent to about 49 percent depending on cultivar, and after ten days from about 19 percent to about 48 percent. Longer exposure was worse for seven of the eight.
UF states the conclusion in a form that belongs on the wall of anyone who keeps plants in a cold apartment. Chilling injury can be either visible or invisible, and the invisible kind may be wrongly diagnosed as insufficient fertilization or other culture practices.
Wrongly diagnosed as insufficient fertilization. A plant that sat in a cold window all winter, then sits there in April not growing, gets fed. The feeding does nothing, because the problem happened months ago and is not a shortage of anything. UF even anticipates the timing: it could explain why some cultivars recover slowly in spring even when temperature becomes optimal and nutrient supply is adequate.
Clemson arrives at the same warning from an entirely different direction, writing about outdoor cold damage: The signs of cold damage can be confusing, since some damage may not be evident until months later.
Two independent extension sources, one indoor and one outdoor, both saying the injury and the symptom are separated by a long gap. If a plant is being fed for slow spring growth, and it spent the winter near glass, the winter is the better suspect. Slow growth with no other explanation is also covered from the light side in houseplant winter care, and the two causes stack rather than compete.
Peace lilies are worth singling out here, since they are one of the plants most often kept in a dim, cool corner. UF puts reduced growth at or below 50°F for the species and lists its cold injury as both visible and invisible, which is covered alongside its other failure modes in peace lily drooping.
What houseplant cold damage looks like when it does show
Three different appearances, depending on the plant and the severity.
Dark, greasy-looking patches, between the midvein and the leaf edge, on the upper surface. This is the Chinese evergreen signature above, appearing about two days after the cold event rather than during it.
Blackening that starts at tips and edges. UF describes the peace lily pattern at damaging temperatures: Chilling injury initiated from leaf tips and edges and progressed inwardly, with injured leaf areas becoming necrotic, then turning black. If you have looked up cold draft plant leaves turning black, this is the mechanism, and the tip-inward direction is the identifying feature.
Water-soaked and wilted tissue that turns dark within hours or days, which Clemson describes for freezing and chilling damage alike. This is the severe end, and usually means an actual cold event rather than a chilly sill.
Two things separate all of these from the problems they get confused with. Cold damage appears on the side facing the cold and on the older leaves, so it has a geography. And it arrives after an event, not gradually, which is the opposite of how a nutrient problem develops. If the pattern is even, spreading, and slow, read yellow leaves instead.
How cold is your windowsill, actually?
Colder than the room, and nobody knows by how much without checking.
Missouri Extension makes it an instruction rather than an observation: In winter, the temperature near windows may be cooler than elsewhere in the house, and so On cold nights, check temperatures close to windows.
That is a five dollar problem to solve. A cheap indoor thermometer left on the sill overnight, read in the morning, converts every guess in this article into a number for your specific apartment, and a min-max model is the right variety since the number you want happened while you were asleep. Which instruments are worth owning, and which one usually is not, is in moisture meter for houseplants. In a rental with single glazing and no say over the windows, that number is the single most useful thing you can know about where a plant lives.
One detail from the same page is easy to get exactly backwards, since it looks like protection: If drapes are drawn around a plant placed near a window, the temperature may be too cool. Closing the curtain in front of a plant puts it outside the heated room, in a narrow cold pocket against the glass, for the whole night. The curtain has to go behind the plant or the plant has to come off the sill.
Sudden change matters as much as the level. Missouri notes that plants like African violet can suffer chill injury when their leaf temperature fluctuates suddenly, advising to Keep such plants away from cold drafts and use water that is room temperature when watering. Maryland gives the same instruction in general form: Protect them from sudden, brief changes in temperature.
Which quietly rules out a common winter habit. Opening a window for two minutes to air out a room, in January, with a plant on that sill, is a sudden brief change in temperature applied directly to the most sensitive leaves on the plant.
The radiator under the window problem
Rented apartments put the heat source directly below the coldest surface, and the plant ends up in both.
Missouri is unambiguous about one half of it: Do not put plants at windows that have hot air registers or radiators directly below them, because Hot air blowing on a plant often causes leaves to brown on the edges and, occasionally, to drop or die. Maryland agrees that indoor plants are sensitive to drafts or heat from registers.
The advice assumes you can choose a different window. In a lot of apartments the radiator sits under every window, because that is where heating systems have been put for a century, and the answer has to be positional rather than a matter of picking a better room. The plant that suffers most from getting this wrong, because three extension services name drafts for it and one says it prefers to stay in one place, is the rubber plant: rubber plant care mistakes maps where the drafts cross a room.
The summer counterpart is an air conditioning vent, which Clemson names directly in one species' care sheet alongside chilling as a cause of leaf drop: schefflera dropping leaves.
What works, in rough order of effort:
Get the plant off the sill and onto a stand a foot or two into the room. This is the whole fix most of the time. It leaves the cold pocket and the hot updraft at once, and costs a little light, which is the trade covered in east vs west facing windows.
Put something solid between the radiator and the plant. A shelf, a board, a tray. The problem is the rising column of dry hot air, and it is easy to deflect.
Move it for the season, not permanently. The conflict only exists while the heating runs. Nothing stops a plant going back to the sill in April, and a plant that moves twice a year is a normal plant.
Browning edges from that hot updraft look like a humidity problem and are usually treated as one, which is worked through in brown tips on houseplant leaves.
The temperature bands, collected
| Range | What it is | What happens |
|---|---|---|
| 70 to 80°F day, 60 to 68°F night | UMD's target for foliage plants | Normal growth |
| Around 55°F | Ordinary sill temperature on a cold night | Visible injury in sensitive cultivars after 24 hours |
| Around 52°F | Cool sill, cold snap | No visible injury, measurably smaller plant 45 days on |
| Below 40°F | Missouri's injury threshold for tropical foliage | Real damage, likely visible |
| Below 32°F | Freezing | Water-soaked tissue, blackening, often death |
Read the middle two rows together. They are only three degrees apart, and one produces marks you can see while the other produces a plant that never quite gets going.
Common questions
What temperature is too cold for houseplants? Below about 60°F at night is outside the range Maryland Extension gives for foliage plants, and Missouri notes that some tropical foliage plants can be injured below 40°F. Damage does not need freezing: UF found visible injury in Chinese evergreen after 24 hours at 55°F.
Are houseplants near cold windows a problem? They can be, and the gap is invisible from across the room. Missouri Extension advises checking temperatures close to windows on cold nights, because the air there may be much cooler than the rest of the house. Leaving a thermometer on the sill overnight settles it for your apartment.
Why are my plant's leaves turning black after a cold draft? That is the chilling injury pattern. UF describes it in peace lilies as starting at leaf tips and edges and moving inward, with the damaged areas going necrotic and then black. Symptoms often show up a day or two after the cold event rather than during it.
Can a plant recover from cold damage? Partly. Damaged leaf tissue does not repair, so what is black stays black, but the plant can carry on and grow out of it. UF found in Chinese evergreen that leaves with under half their area injured could stay alive for months, while leaves past that point yellowed and dropped. Recovery may be slower than expected: UF suggests invisible chilling explains plants that recover slowly in spring even when conditions are good.
Is a radiator under a window bad for plants? The combination is, since the plant gets dry hot air from below and cold glass in front. Missouri advises against placing plants at windows with radiators or hot air registers directly beneath, warning that hot air blowing on a plant browns leaf edges. Moving the plant a foot or two into the room solves both halves.
One thing to do before winter
Put a thermometer where your most sensitive plant sleeps, and read it in the morning.
Not the room temperature, the sill temperature, behind the curtain if the curtain closes. If it reads in the 50s, you have located a source of houseplant cold damage that will not show up as damage, and you have found it in August instead of working backwards from a plant that refuses to grow next April.