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Unlike most large-leaved plants kept indoors, colocasia has a real, hard-edged annual cycle. It does almost nothing until the ground and the air are warm, grows explosively for three or four months, and then shuts down completely, dying back to a corm that will sit through winter with no leaves at all. Understanding that shape removes nearly all the confusion, because the same action is correct in one month and fatal three months later.
There are only two decisions that really matter. The first is when to start the warm, wet, heavily fed regime in spring, and the answer is later than most people think: not until nights are reliably above 54F (12C). The second is when to stop it in autumn, and the answer is earlier than most people think: as soon as nights drop below about 59F (15C) and the plant stops replacing leaves. Everything else follows.
| Phase | Trigger | Water | Feed | Position |
|---|---|---|---|---|
| Waking | Room or soil warming, first bud moving | Sparingly, top inch damp | None | Warm and bright indoors |
| Establishing | Two or three leaves standing | Regularly, never dry | Weak liquid feed fortnightly | Sheltered outdoors by day |
| Full growth | Nights above 54F (12C), settled warmth | Standing water, topped up daily | Weak feed every second watering | Final sunny sheltered spot |
| Slowing | Nights below 59F (15C) | Tray removed, interval extended | Stop feeding | Same spot, or move under cover |
| Shutdown | Frost forecast | Almost none | None | Lift the corm or bring the pot in |
| Dormant | No leaves | A splash monthly at most | None | Frost free, 50 to 59F (10 to 15C), dark is fine |
Spring: waking it up
A stored corm or an overwintered pot starts moving on its own once it warms, usually showing a fat pointed bud at the crown. Bring it into warmth and light at that point, pot it up if it was stored bare, and water lightly. Resist the urge to soak it: until there are leaves to drink, extra water only sits in the compost, and this is the season when people rot corms that survived the whole winter perfectly well.
Once two or three leaves are standing and clearly growing, the plant changes character completely and you can begin feeding and watering in earnest. Harden it off over a week before it goes outside permanently, giving it a few hours outdoors each day and bringing it in at night, so the leaves that grew in indoor light do not scorch in the first burst of sun.
- Pot up as the bud moves Set the corm with its shoulder level with the surface in a pot two sizes larger than last year, in a heavy water-holding mix with slow-release feed. Water once, then leave it.
- Keep it warm to trigger growth Hold it at 70 to 77F (21 to 25C) if you can. Warmth is what starts this plant, and a corm kept cool in spring simply sits there and does nothing for weeks.
- Start feeding at two leaves Begin a weak liquid feed once there are two proper leaves. Feeding a leafless corm does nothing useful and pushes salts into compost that is not being flushed.
- Harden off over a week Increase outdoor time daily from two hours to all day, keeping it out of harsh midday sun at first, then leave it out overnight only once nights are above 54F (12C).
Summer: keeping up with it
This is the easy part, provided you do not underestimate the demand. A colocasia in full summer can push a new leaf every seven to ten days, and each one is bigger than the last. Keep the tray full, feed weakly and often, and cut off leaves as they tire so the plant is not maintaining tissue it has finished with. Expect to pot on mid-season if the plant starts wilting daily or the new leaves come smaller.
This is also when to watch the undersides of the leaves for spider mites and to check that the plant is not sitting somewhere windy. A midsummer move of a few feet into shelter saves the last two months of leaves from being shredded.
Keeping a running count of leaves is the simplest useful record there is. Note the date each new leaf opens. A plant that opened a leaf every eight days in early summer and has now slowed to one in three weeks is telling you it is pot bound, hungry, or that the season is ending.
Autumn: the controlled shutdown
The end of the season is where plants are actually lost, and it is lost by inaction. As nights cool below 59F (15C), take the pot out of standing water and let the compost start drying between waterings. Stop feeding. The plant will begin to yellow off its leaves one by one, which is correct and not a problem to be fixed.
Act before the first frost, not after it. Frost blackens the leaves in a single night and the corm then goes into storage wet and damaged rather than clean and firm. You have two options. Bring the whole pot indoors somewhere cool and frost free and simply stop watering it, or lift the corm and store it bare. Both work. Bare storage takes less space and lets you inspect the corm.
- Cut the foliage down Once the leaves have yellowed, or immediately if frost has blackened them, cut the stalks off about two inches (5 cm) above the corm with a clean blade. Wear gloves.
- Lift and clean the corm Tip the pot out, shake and brush the compost off, and trim the roots back to short stubs. Do not scrub or soak it. Any soft or damaged tissue gets cut away now, back to firm cream flesh.
- Cure it for a week Leave the corm somewhere dry, airy and out of the sun for about a week so the cut surfaces harden and any surface damp evaporates. A corm packed away damp will rot.
- Pack it dry and cool Put it in a paper bag or a box of dry sand, wood shavings or vermiculite, somewhere frost free at 50 to 59F (10 to 15C). Dark is fine. Never seal it in plastic.
- Check it monthly Look and squeeze once a month. Firm is fine. Soft means cut out the rot immediately and repack it dry. Shriveled and very light means the store is too warm and dry, so move it somewhere cooler.
Winter, and what to write down
Winter is almost entirely inaction. A stored corm needs nothing but a monthly look. A pot kept indoors needs perhaps a splash of water once a month, just enough that the compost is not dust dry, and no feed at all. Keep it above freezing and out of a heated dry room if you can, because warm dry air over winter either forces weak growth or dries the corm out.
Close the year by writing three things in your records: the date the plant went into standing water in spring, the date it came out in autumn, and the size and firmness of the corm when you lifted it compared with the year before. A corm that comes out bigger every year means your season is long enough and your feeding is right. One that comes out smaller each year means the plant is being started too late, stopped too early, underfed, or kept too cold in summer, and you have a whole winter to think about which.
Also record where each corm came from and how old it is. Once you have divided a plant a couple of times you will have several corms of different ages in storage, and by spring they are indistinguishable. Labeled bags save a lot of guessing at potting time.