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Calatheas grow on a forest floor beneath a closed canopy, and the pattern on the leaf is worth more to them than raw brightness. An hour of direct summer sun bleaches the color out of a leaf permanently, and no amount of correct watering brings it back.
The usable test is a shadow test. Hold your hand a foot above the plant at midday. A soft shadow with a blurred edge is right. A hard shadow with a crisp edge means direct sun is reaching the leaves and you should move it or add a curtain. No shadow at all means the spot is too dark and new leaves will come out small with the markings washed out.
| Position | Verdict | What you will see |
|---|---|---|
| East window, no curtain | Ideal | Strong markings, leaves at full size |
| North window, at the glass | Very good | Reliable all year, slow but clean growth |
| South or west window behind a sheer curtain | Good | Watch for scorch in high summer, move it back |
| Three to six feet into a bright room | Workable | Slightly smaller leaves, color still holds |
| South window, no curtain | Harmful | Bleached patches within days, then dry brown |
| Interior room, no window | Not viable | Leaves shrink, markings fade, plant declines |
Faded, washed out markings are the classic sign of too much light. Small leaves on long stalks reaching towards the window are the sign of too little. The two errors look nothing alike once you know what to look for.
Temperature has a hard floor
This is a tropical plant with very little cold tolerance and no dormancy to fall back on. It is comfortable between 64 and 79F (18 and 26C) and it starts suffering below 61F (16C). Below 54F (12C) leaves blacken at the edges within a couple of days and the damage is permanent.
The danger is rarely the daytime room. It is the overnight temperature at a window in winter, which can be fifteen degrees colder than the middle of the same room. If a plant looks fine in the day and keeps producing damaged leaves, measure the temperature at its position at night before you change anything else.
| Temperature | Effect on the plant | Action |
|---|---|---|
| 79F (26C) and above | Grows fast, dries out fast | Water more often, raise the humidity |
| 64 to 79F (18 to 26C) | Ideal, steady growth | Normal care |
| 57 to 64F (14 to 18C) | Growth stops, water use falls | Stretch the watering interval, stop feeding |
| Below 54F (12C) | Leaf edges blacken, roots damaged | Move it at once, do not water until warmer |
Drafts do more damage than dry air
A calathea in dry but still air holds up far better than one in humid but moving air. Air blowing across a leaf strips moisture from the edge faster than the roots can replace it, and the edge crisps. Almost every plant with severe edge browning turns out to sit in a moving air stream that the owner had not registered as one.
- Find the drafts before you place it Hold a strip of tissue paper where you want the plant, at leaf height, and watch it for a minute with the heating running. Any visible movement is enough to damage the leaves over weeks.
- Keep it away from heating and cooling Never directly above a radiator, in front of a heating vent, or in the throw of an air conditioner. Three feet of clearance and something between the plant and the outlet.
- Watch entrance doors and stairwells A hall by an outside door gets a slug of cold dry air every time someone comes in. In winter that is enough on its own to mark every leaf.
- Leave a gap at a window in winter Keep leaves from touching cold glass, and pull the plant back into the room at night, or draw the curtain on the room side so the plant is not shut into the cold.
Rooms that suit it
The plant's requirements line up unusually well with a bathroom or a kitchen, provided the light is there, because both are naturally humid. That is worth more than any misting routine.
| Room | Humidity | Usual problem | Verdict |
|---|---|---|---|
| Bathroom with a window | High | Often too dark if the window is small or frosted | Excellent if it is bright enough |
| Kitchen away from the hob | Moderate to high | Heat and fat from cooking | Good, keep it off the worktop by the hob |
| Living room | Low in winter | Heating and drafts | Workable with a humidifier |
| Bedroom | Low | Usually the driest room in the house | Group it with other plants |
| Conservatory | Variable | Direct sun and wild temperature swings | Only with heavy shading and stable heat |
A frosted bathroom window gives less light than it looks like it does. If the markings on new leaves are fading, that is the reason, and the plant needs to be right against the glass.
Move it with the seasons
Two moves a year cover most of it: one in late spring as the sun gets high and strong, and one in autumn as the light weakens and the heating starts.
- Late spring Pull it back from any south or west aspect, or add a sheer curtain. The sun that was harmless in early spring will bleach leaves within a fortnight of the weather turning.
- Autumn Move it back towards the light as days shorten, and at the same time work out where the heating will blow once it comes on. Change the position before the heating starts, not after the first damaged leaf.
- Turn the pot a quarter every fortnight The leaves orient themselves to the light and the plant leans within a couple of months if you leave it. A regular quarter turn keeps it upright and even.
- Do not put it outside Unlike most houseplants, a calathea gains almost nothing from a summer outdoors and picks up wind damage, sun scorch and spider mites. Leave it where it is.
Keep a note of where it has stood
Record the position and the date whenever you move the plant, and note the temperature and humidity at that spot if you have a meter. Then note whether the next leaf to open was clean or marked.
Leaves take two to four weeks to open, so a change in position shows up in the leaf after next, not the one currently unfurling. Without a written date you will attribute the result to the wrong move, which is why so many people conclude that this plant is simply unpredictable.