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An alocasia grows under a broken canopy, so it wants a lot of light without the sun itself falling on the leaf. The practical test is that the spot should be bright enough to read comfortably without a lamp, and a hand held above the plant should cast a shadow with a soft but clearly defined edge. If the shadow is hard and sharp, that is direct sun and the leaf will scorch.
Too little light does not kill the plant outright. It produces a slow decline: the new leaves come smaller than the ones they replace, the stalks stretch and lean, and the plant stops replacing leaves as fast as it loses them. Because it takes months, most people blame watering when the real problem is that the plant is eight feet from a window.
| Position | Light level | How the plant responds |
|---|---|---|
| East window, no curtain | Ideal | Soft morning sun, steady new leaves |
| South or west window behind a sheer curtain | Ideal | Strong diffused light without scorch |
| Three feet back into the room | Slightly short | Holds, but new leaves come smaller |
| Eight feet or more from a window | Too dark | Stalks stretch, leaf count drops each month |
| Unshaded south window sill in summer | Too strong | Pale bleached patches within a day or two |
Light falls away much faster than it looks to the eye, because your eyes adjust as you walk into a room. A spot that feels bright to you can be a small fraction of the light at the glass.
Warmth matters more than most people expect
This is a warm growing plant with no real cold tolerance. It grows properly above about 68F (20C), slows noticeably below 64F (18C), and stops altogether around 59F (15C). Below 50F (10C) the leaves collapse and the corm is at risk, and a night at freezing point will kill it outright.
The temperature that matters is the night temperature at the plant, not the daytime figure on the thermostat across the room. A window sill in an unheated room can be fifteen degrees colder at three in the morning than the room was at bedtime, and cold plus wet compost is the exact combination that rots a corm.
- Move it off the sill at night in winter Glass loses heat fast, and a leaf touching cold glass blackens where it touches. Move the plant a couple of feet into the room in the evening and back to the window in the morning, or fit an insulating blind.
- Keep it away from heater drafts A stream of hot dry air from a radiator or a vent crisps the leaf margins within days and encourages spider mites. Two or three feet of clearance is enough.
- Watch doors and air conditioning A cold blast every time an outside door opens, or air conditioning blowing directly on the plant, causes leaves to yellow and drop with no obvious cause. Neither shows up when you check the pot.
Standing it outside for the summer
An alocasia does very well outdoors in summer shade and often puts out its biggest leaves of the year there. The move has to be gradual, though, because leaves grown indoors have no protection against outdoor light levels and will bleach in a single afternoon.
- Wait for the nights Move it out only once nights are reliably above 59F (15C), and bring it back in well before nights drop below that in autumn. Judge by the overnight low, not the daytime warmth.
- Start in full shade Begin under a porch or in the shade of a tree and increase the light over two weeks. Skipping this step scorches every leaf, without exception.
- Shelter it from wind and heavy rain The large thin leaves tear in wind and the long stalks snap. Prolonged rain keeps the pot saturated for days, which is the corm rot risk again. A sheltered spot under an overhang solves both.
- Clean it before it comes back in Wash the leaf undersides and scrub the outside and base of the pot before it returns indoors. Outdoor plants pick up mites, scale and slugs, and an infestation carried into a warm dry room in autumn spreads very quickly.
Turning and leaning
Alocasia stalks are strongly phototropic and the whole plant will lean towards a window within a couple of weeks. Give the pot a quarter turn every week or two and it stays upright and even.
A plant that leans hard despite regular turning is telling you the light is marginal. Turning corrects the shape, but if the lean returns strongly within days, move the plant closer to the window rather than turning it more often.
Keeping it away from children and pets
Every part of an alocasia contains calcium oxalate crystals. Chewing a leaf causes immediate burning and swelling of the mouth and throat, and the sap irritates skin and eyes. This is the main reason to think about position rather than just light.
Put it where a crawling child or a cat cannot reach the leaves: a high shelf, a plant stand out of a walkway, or a room they do not have unsupervised access to. Wear gloves whenever you cut, divide or repot it, and wash your hands afterwards even if you did.
The trailing drips from guttation carry the same sap. If the plant sits above a surface where a pet drinks or a child plays, move it or put a tray underneath.
A position checklist worth writing down
Because the effects of position show up over months rather than days, it is worth keeping a short written record of where the plant has lived and what it did there. Note the date of each move, the window aspect and the rough distance from the glass, and the date each new leaf opened. After one full year you can see plainly which spot produced leaves and which one merely kept the plant alive.
Add the overnight low in the room in the coldest week of winter, and whether the plant went dormant. Next winter that one figure tells you immediately whether to move it or leave it, instead of guessing again.