Gadenin日本語Get the appThis one is not like your other plants
Almost every rule you have learned about not letting a pot sit in water is wrong for colocasia. It comes from the muddy margins of streams and flooded ground, and it will grow happily with the base of the pot standing in an inch or two (3 to 5 cm) of water for the whole of the growing season. Given that, it puts out leaves faster and larger than it ever will in a pot you let dry between waterings.
The mirror image of that tolerance is that it has no reserve at all. The leaves are enormous, thin and full of water, and they lose it fast. A pot that goes dry on a hot afternoon produces a total collapse in two or three hours, with every leaf hanging straight down the stalk. It usually stands back up overnight after a soak, but each hard wilt scorches the leaf margins permanently, and two or three of them in a summer will cost you the leaf altogether.
Standing water is for the growing season only, and only while the plant is in leaf and warm. The same tray of water in a cold room in winter rots the corm within weeks. The rule flips completely at the end of the season.
How often, and how much
In an ordinary pot with no water tray, a colocasia in full summer growth wants water every day, and a large plant in a small pot in wind and sun may want it twice. That is not an exaggeration or a worst case. The plant is transpiring several times its own pot volume of water a week through those leaves, and the interval that suits your other container plants will not keep up.
The practical fix is to stop trying to keep pace by hand. Put the pot in a deep saucer, a shallow bowl or a cachepot with no drainage, and keep an inch or two of water in it. Refill it when it runs dry rather than watering the surface. Water taken up from below reaches the roots evenly and you no longer have to be at home at four in the afternoon.
| Setting | Water level in the tray | Top-up interval | Watch for |
|---|---|---|---|
| Full sun, hot summer, outdoors | One to two inches (3 to 5 cm), kept topped up | Daily to every other day | Tray empty by afternoon means go to a bigger tray |
| Part shade outdoors | Half an inch to one inch (1 to 3 cm) | Every two or three days | Slower growth but far fewer wilts |
| Bright room indoors, warm | Half an inch (1 cm), allowed to run dry between | Every three or four days | Stagnant water and fungus gnats |
| Cool spell below 59F (15C) | No standing water at all | When the top inch (3 cm) has dried | Compost staying wet for a week and souring |
| Dormant, leafless, over winter | None | A splash once a month at most | Any softness at the top of the corm |
Reading a wilt correctly
A wilted colocasia is not automatically a thirsty one, and the wrong diagnosis here is expensive. Put a finger two inches (5 cm) into the compost before you do anything. Dry compost with a wilt is thirst, and the plant will be upright again a few hours after a thorough soak. Wet compost with a wilt is something else, and adding water makes it worse.
| What you see | Compost | Cause | What to do |
|---|---|---|---|
| Every leaf hanging by mid-afternoon | Dry | Simple thirst | Soak the pot until it runs through, then set up a tray |
| Wilted and stays wilted after watering | Wet | Rotting corm or roots | Unpot, cut away soft tissue, repot dry and hold back water |
| Wilts on hot days only, recovers each evening | Damp | Leaf area outrunning the root system | Move to afternoon shade and pot on this season |
| Wilted after a cold night | Damp | Chill, not water | Leave it alone. Do not water into cold compost |
| One old leaf droops, the rest fine | Any | That leaf being retired | Normal. Cut it off at the base |
The stalks are the early warning. They stiffen and stand almost vertical on a well supplied plant, and they soften and lean outward before the leaf blade itself starts to fold. If the stalks have begun to lean by lunchtime, water before the collapse happens.
Water quality, feeding and the mineral marks
A plant drinking this hard also draws through a great deal of whatever is dissolved in your water. In a hard water area you will see chalky white rings on the leaf edges and a crust on the compost surface within a season. Neither harms the plant, but if it bothers you, collect rainwater for it. Rain is also warmer than the tap in summer, which the plant prefers.
Because water passes through so quickly, feed dissolves and washes out just as fast. A colocasia in growth is a heavy feeder, and a weak liquid feed at every second watering suits it better than a strong feed once a month. If you are using a tray, put the feed in the tray rather than on the surface so it is taken up rather than sitting on top of the compost.
Water standing in a tray for weeks in heat goes stagnant and breeds mosquito larvae and fungus gnats. Tip the tray out and refill it fresh once a week rather than only ever topping it up.
The autumn change, and what to record
The single most useful thing you will do all year is to stop the wet regime at the right moment. Once night temperatures fall below about 59F (15C) and the plant stops replacing leaves, take the pot out of its tray, let the compost drain and start extending the interval. From there you are heading toward the dormant regime, where the compost is barely damp and the corm is kept cool and dry rather than wet.
Write down two dates each year and this plant becomes easy. The first is the day you set up the water tray in spring, and the second is the day you took the pot out of it in autumn. Add the number of leaves standing when you did it. After two seasons you will know your own climate's window far better than any general advice, and you will stop losing corms to a tray that stayed full three weeks too long.
- Note the day the tray goes in Record the date you first stood the pot in water and what the night temperatures were doing. This is the date you will reuse every spring, and it is far more reliable than watching the calendar.
- Note the day the tray comes out Record the date the plant left standing water, together with how many leaves it still had. A plant that still had five healthy leaves came out too early. One with a single tattered leaf came out slightly late.
- Note every hard wilt A one-line note each time the plant collapsed, with the weather that day, tells you next year whether the pot is too small, the position too sunny, or you simply need a deeper tray.