Gadenin日本語Get the appThe corm is what you are protecting
An alocasia does not grow from a fibrous root mass like most houseplants. Under the compost there is a firm, upright corm, roughly the size and shape of a small potato or a short cigar, and every leaf and every root comes out of it. If the corm is sound the plant recovers from almost anything. If the corm goes soft, nothing you do to the leaves matters.
That single fact decides how you water. The roots want moisture, but the corm sits in the middle of the pot and rots if it is surrounded by wet compost for weeks at a stretch. The target is a pot that swings between damp and nearly dry, never one that is permanently wet and never one that is bone dry for days.
| Situation | What the compost is doing | What to change |
|---|---|---|
| Plastic pot, away from the window | Dry on top, wet in the middle for weeks | Lengthen the interval and check with a skewer |
| Terracotta in strong light in summer | Dries within two or three days | Water more often, but still until it runs through |
| Sitting in a cachepot with water in it | Base permanently wet | Lift it out to water and empty the outer pot |
| Room below 59F (15C) | Barely drying at all | Water perhaps once a fortnight, on a mild morning |
Push a finger into the compost beside the stem. You should feel a firm object an inch or two down. If it gives under gentle pressure, the corm is already rotting and no amount of care to the leaves will fix it.
Water when the top third has dried
Rather than counting days, water when the top third of the pot has dried out and the lower two thirds are still faintly damp. In a six inch (15 cm) pot that is roughly the top two inches (5 cm). At that point the corm has had a spell of air and the roots have not been left desiccated.
When you do water, water thoroughly. Half a cup poured on the surface only wets the top, which is the layer that was supposed to dry. Water until it runs freely from the drainage holes, then let the pot drain properly before it goes back on its saucer.
- Learn the weight of the pot Lift the pot immediately after a thorough watering and again three days later. The difference is obvious once you have felt it twice, and weight is a far better guide than the look of the surface.
- Use a wooden skewer Push a skewer down the side of the pot to about two thirds depth and pull it out. Dark and cool means wait. Dry and clean means water. This is the most reliable check in a pot over eight inches (21 cm).
- Water at room temperature Cold water straight from the tap chills the corm and checks growth for days. Let a jug stand overnight, or mix in enough warm water that it feels tepid on your wrist.
- Empty the saucer Tip away anything still standing after half an hour. Water left under the pot keeps the base of the compost permanently wet, and that is exactly where corm rot begins.
Intervals through the year
These are for a plant in a pot around eight inches (21 cm) across in a normal living room. Treat them as a starting point and adjust from what the compost is actually doing, not from the calendar.
| Season | Room temperature | Interval | Notes |
|---|---|---|---|
| Spring | 64 to 75F (18 to 24C) | Every four to six days | Restart feeding once a new leaf is visibly moving |
| Summer | Above 75F (24C) | Every two to four days | Highest water use of the year. Never let it wilt hard |
| Autumn | 59 to 68F (15 to 20C) | Every eight to twelve days | Stretch the interval as leaves stop being replaced |
| Winter | 50 to 59F (10 to 15C) | Every two to four weeks | A sip, on a mild morning. Do not soak it |
If the plant has gone dormant and has no leaves at all, it still wants a small amount of water about once a month. Completely dry compost for a whole winter shrivels the corm just as surely as wet compost rots it.
Humidity is not a substitute for watering
Alocasia leaves are thin and lose water fast, so dry indoor air shows up as crisp brown edges and margins even when the roots have plenty. That is an air problem, not a thirst problem, and adding more water to the pot to fix it is how people rot the corm while trying to help.
Raise the humidity around the plant instead. A tray of pebbles with water below the pot base, a group of plants standing together, or a humidifier in a heated room all work. Misting helps for the twenty minutes it lasts and is mostly useful as a chance to wet the leaf undersides, where spider mites live.
Water dripping from the leaf tips is normal
You will find beads of water hanging from the pointed tips of the leaves, usually in the morning, and sometimes a small damp patch on the floor below. This is guttation. When the roots are taking up more water than the leaf is transpiring, the plant pushes the excess out through pores at the leaf margin. It is a sign of an actively growing plant with a working root system, not a disease and not a pest.
It does mean the pot is well supplied, though. Persistent heavy dripping every morning through autumn, when growth is slowing, is a hint that you are watering on a summer interval into a season that no longer needs it. The drips leave faint white marks on furniture because of dissolved minerals, so put something under the pot rather than trying to stop the plant doing it.
Guttation drips are clear and watery. Sticky droplets that are still sticky when dry are honeydew from an insect, not guttation, and mean you should turn the leaves over and look.
Reading the symptoms
The same leaf symptom means opposite things depending on whether the compost is wet or dry, which is why the first move in every diagnosis is to put a finger in the pot.
| Symptom | If the compost is wet | If the compost is dry |
|---|---|---|
| Whole plant drooping | Corm or root rot. Stop watering and unpot it | Simple thirst. It stands up within hours of watering |
| Leaf yellowing from the outside in | Waterlogged roots. Repot into a coarser mix | Old leaf being retired. One at a time is normal |
| Dry brown leaf edges | Damaged roots cannot supply the leaf | Dry air. Raise the humidity, not the watering |
| A new leaf browns before it unfurls | Cold and wet together at the corm | Air too dry for the furled leaf to slide open |
When you genuinely cannot tell, slide the plant out of the pot and look. Pale, firm roots and a hard corm mean it is a watering interval problem you can correct. Brown mush and a smell mean you are into rot and need to act on the corm itself.