Leaves curling inwards or under
A curled leaf is a leaf reducing its surface. Heat, thirst, cold and pests all cause it, and the direction of the curl narrows it down.
What it usually is
1 Heat or strong sun
| How to tell | Leaves curl upwards or fold along the midrib during the hottest part of the day and relax again by evening. The plant sits in direct sun or near a heat source. |
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| The fix | Move it out of the midday sun or a metre back from the radiator. A leaf folding is a leaf reducing the area it exposes, which is sensible behaviour rather than damage, but a plant doing it every day is in the wrong place. |
2 Thirst
| How to tell | Curling that comes with dull colour and compost that is dry to the second knuckle. The leaf feels papery rather than firm. |
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| The fix | Water thoroughly until it runs from the bottom and empty the saucer. A plant that curls from thirst usually opens again within hours, which is a useful confirmation that you were right. |
3 Cold
| How to tell | Curling with a darker, slightly translucent look, on a plant near a window in winter or one that spent a night in a cold room. Often only the exposed side is affected. |
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| The fix | Move it off the sill and away from the glass. Cold damaged tissue does not recover, so remove the worst leaves once the plant is warm again and let new growth replace them. |
4 Aphids or thrips on the new growth
| How to tell | The newest leaves curl tightly and stay curled, and unrolling one carefully shows small insects, sticky residue or fine silvery scarring. Older leaves below are flat and clean. |
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| The fix | Wash the growing tips under a tap, both sides, and repeat after five days and again five days later. Isolate the plant while you do it and check the plants either side of it. |
Through the year. Heat curling belongs to summer afternoons and to the first weeks the heating is on. Cold curling belongs to winter windowsills. Pest curling can be any time and is commonest on soft spring growth.
A leaf that curls is trying to lose less water. The pores are on the underside, so folding inwards shelters them from moving air and from the sun, and every plant does it as a short term measure. The question is whether it is a response to an afternoon or a permanent state.
Watch the plant at two times of day. A leaf that curls at two in the afternoon and lies flat again by nine in the evening is doing its job and telling you the spot is hot or bright rather than that the plant is ill. A leaf that is curled morning and night has a supply problem: either there is no water in the pot, or the roots cannot move it.
The direction of the curl is a useful clue. Curling upwards and inwards along the length of the leaf is usually heat or light. Curling downwards, with the leaf drooping as well as rolling, is more often watering, at either extreme. Tightly curled new growth that never opens is a pest, and the pest will be inside the curl.
Cold does something different again. It gives a curl with a darker, greasy or slightly transparent look to the tissue, often only on the side of the plant nearest the glass, and it appears overnight rather than through the day. A plant behind a closed curtain on a January night can be several degrees colder than the room it is nominally in, which is why the same plant is fine in the day and damaged by morning.
The practical order is: feel the compost, look at the time of day, look at the underside and the inside of the new growth, and then look at where the plant is standing. Three of the four causes are solved by moving the pot rather than by treating the plant, which is worth remembering before reaching for a bottle of anything.
Entries that name it
What the journal says about this symptom on each plant.
| Aloe vera | Long drought, or roots damaged by rot and unable to take up water. Check the compost first. Dry means water it; damp means unpot and look at the roots. |
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| Calathea | The compost has dried out, or the air is too dry. Water more evenly and move it somewhere more humid. Leaves that curl from thirst open again within a day of watering. |
| Chinese evergreen | Cold, a draught, or very dry air. Keep it above 16 degrees and away from doors and vents. It is more sensitive to cold than most houseplants. |
| Chinese money plant | Too much light if they cup downwards, or too little if they dome upwards. Move it out of direct sun, or nearer a window, depending on which way the leaves curl. New growth comes in flat once the light is right. |
| Fishbone prayer plant | Dry compost, or a cold draught from a door. Water it and move it somewhere steadier. Folding up at night is normal and is what the whole family does. |
| Green beans | Aphids on the growing tips. Wash them off under a tap or with soapy water, and check again in five days. |
| Prayer plant | The compost dried out, or the air is too dry. Water more evenly and improve the humidity. Leaves curled by thirst open again within a day of a drink. |
| Rattlesnake plant | Dry compost, or a cold draught. Water it and move it away from the door. Some curling at night is normal, because the whole family folds its leaves up in the dark. |
| Stromanthe | Dry compost or a cold draught. Water it and move it away from the door. Some folding at night is normal and is what the family is named for. |
| Tomato | Heat, wind, or over enthusiastic pinching out. Leaves that curl upward in hot weather usually recover overnight. Persistent curling with distorted growth suggests weedkiller drift on the compost. |
Questions from the margin
- Why are my plant's leaves curling?
- A curling leaf is reducing the surface it exposes. Watch it at two times of day: a leaf that curls in the afternoon and lies flat by evening is responding to heat or bright sun, and one that is curled morning and night has a water supply problem.
- What does it mean if only the new leaves curl?
- Look inside the curl. Tightly curled new growth that never opens usually has aphids or thrips inside it, and the older leaves below will be flat and clean.
Checked against RHS, Houseplants: leaf problems; Utah State University Extension, Environmental leaf damage.