Gadenin日本語Get the appCuttings do not work, and here is why
People try a leaf in water, or a length of stalk, and nothing ever happens beyond slow rotting. That is not bad technique. An alocasia leaf stalk carries no node and no growth point, so there is nothing in it that can produce a shoot. Every new plant has to come from the corm.
The good news is that the plant multiplies underground on its own, steadily, and all you have to do is separate what it has already made. Tip a mature plant out of its pot in late spring and you will usually find two or three offsets and a scattering of loose corms the size of a pea or a hazelnut.
| Method | What you separate | Time to a leaf | Difficulty |
|---|---|---|---|
| Separating an offset | A small plant with its own roots and leaves | Immediate, it already has leaves | Easy |
| Potting a rooted corm | A firm corm with roots but no leaves | Three to six weeks | Easy |
| Sprouting a loose corm | A pea sized corm with no roots | Six to twelve weeks | Needs patience and warmth |
| Seed | Ripe seed from a spathe | Months, and rarely worth it | Slow and unreliable indoors |
Do all of this in late spring or early summer, when the room is above 68F (20C). Corms separated in autumn go into the cold half of the year with no roots and usually rot instead of sprouting.
Separating an offset
An offset is a small plant that has come up beside the parent, connected at the base and often with its own roots already. This is the easiest and most reliable increase there is, and it costs the parent almost nothing.
- Unpot the whole plant Do this as part of the annual repot in late spring. Lay it on newspaper and wash or brush enough compost away that you can see clearly where the offset joins the parent corm.
- Look for its own roots An offset with three or more roots of its own can be separated straight away. One with none is better left attached for another season, or treated as a corm and sprouted in the next section.
- Cut, do not tear Separate it with a clean sharp blade at the point where the two corms join. Pulling tears the corm tissue and leaves a ragged wound that rots. Dust both cut faces with cinnamon or a fungicide.
- Let the cuts dry, then pot small Leave the cut surfaces to dry in the air for two to three hours. Pot the offset into a pot barely wider than its roots in the same open mix as the parent. A large pot of wet compost around a small corm is fatal.
- Water lightly and keep it warm Water just enough to settle the mix, then keep it barely damp, warm, and out of direct sun. A new leaf within three or four weeks means it has taken.
Sprouting the loose corms
The small round corms you find loose in the compost, from the size of a pea up to a hazelnut, are the plant's real method of increase. Most people tip them out with the old compost without ever realizing what they are throwing away.
A viable corm is firm when you squeeze it and its outer papery skin peels off to reveal something pale and solid underneath. One that gives under your fingers, or that is hollow and light, is spent. Peel the brown papery layer off before you plant it, because that skin slows water reaching the growth point and adds weeks.
- The damp moss method Put a shallow layer of damp sphagnum moss in a lidded clear box, sit the peeled corms on top with the pointed end upwards, and close the lid. Do not bury them. Keep the box somewhere bright but out of direct sun.
- Keep it warm and check weekly Above 75F (24C) they sprout in three to five weeks. Below 68F (20C) it takes twice as long or does not happen at all. Open the box for a minute once a week to change the air, and squeeze out any corm that has gone soft.
- Pot up once roots and a shoot appear When there are roots half an inch (1 cm) long and a visible green shoot, move each one into a two or three inch (5 to 8 cm) pot of the standard open mix, with the top of the corm just level with the surface.
- Wean it off the humidity A corm sprouted in a closed box has grown its first leaf in saturated air and will crisp if you put it straight on an open shelf. Cover the pot loosely for a week and open the cover a little more each day.
Expect around half to sprout, and expect nothing at all for the first three weeks. Corms are not slow to fail, they are simply slow to start, and most are thrown away a fortnight before they would have moved.
How many plants you can reasonably expect
It helps to have a realistic figure in mind before you start pulling a healthy plant apart, because dividing a parent hard sets it back for a season.
| Parent plant | Offsets to expect | Loose corms | What to do |
|---|---|---|---|
| Young, one or two years old | None or one | A few, often unripe | Leave it alone and repot as one plant |
| Mature in a full pot | Two or three | Five to fifteen | Take the rooted offsets, sprout the corms |
| Long unrepotted, crowded | Three or more | Twenty or more | Divide fully, but expect a slow year afterwards |
| Just coming out of dormancy | Hard to judge | Firm and ready | Best moment of all to separate corms |
Why attempts fail
There are only four real reasons an alocasia division fails. It was attempted in the cold half of the year. The piece had no growth point, which is to say it was a leaf or a stalk rather than a corm. It was potted into far too large a pot and the compost stayed wet around it. Or it was given up on after two weeks.
Rule those four out and the success rate is high. A firm corm, warmth above 68F (20C), a small pot of open mix kept barely damp, and six weeks of patience will produce a plant.
Write down the date you separated each piece and where it came from, along with the date the first leaf opened. After one season you will know exactly how long your conditions take, and you will stop discarding corms that simply needed another fortnight.