Gadenin日本語Get the appIt propagates whether you want it to or not
Every rhizome fragment with a node, down to about half an inch (1 cm), will produce a plant given damp soil. Stems that touch damp ground root at the node in a fortnight. Cuttings root in plain water in a week or two. This is not a plant you need technique to increase, and that is exactly the problem: most unintended fish mint in gardens arrives on a spade, in a bag of soil, or in a load of compost that had a fragment in it.
So treat propagation as a two-sided job. One side is producing the one or two plants you actually want, in containers you have prepared. The other side, which takes more care, is making sure that nothing else you handle that season ends up growing somewhere you did not choose.
Never give fish mint away without telling the recipient exactly how it spreads, and never plant it in someone else's garden on their behalf.
Division: the method to use
Division is the standard way to increase it and the way to renew a pot that has become solid rhizome. Do it in early spring before growth starts, or in early autumn once the weather cools. Avoid midsummer, when a divided plant sulks and the cut surfaces rot in warm wet compost.
- Work on a hard surface Tip the pot out onto a tarpaulin, a bench or a paved area, never onto soil or a lawn. Fragments fall off constantly during division and every one that lands on soil roots.
- Break off a piece with three or more buds Look for plump white rhizome with visible growth points. A piece three to four inches (8 to 10 cm) long with several buds establishes fastest and makes a full pot in one season.
- Cut with a blade, do not tear Use clean pruners or a knife. Torn rhizome crushes and rots at the wound in wet compost, whereas a clean cut callouses within days.
- Pot it two inches deep Lay the piece horizontally two inches (5 cm) below the surface in ordinary moist compost, buds upwards. Water it in and keep it damp and shaded.
- Expect shoots in two to three weeks At soil temperatures above 55F (13C) shoots break the surface within about a fortnight. Nothing showing after a month usually means the compost dried out, not that the piece failed.
- Sweep the surface afterwards Collect every fragment from the bench or tarpaulin before you move anything. Rinse tools and boots away from beds, because pieces stick to both.
Stem cuttings
Cuttings are worth using when you want to move a plant without disturbing rhizomes, or when you want a small pot from a friend's plant without carrying soil home. They root very easily but give a smaller plant in the first year than a division does.
Take a shoot four to six inches (10 to 15 cm) long in late spring or early summer, cut just below a node, and strip the lower leaves. Stand it in a jar of water in a shaded place and roots appear in seven to fourteen days, or push it straight into damp compost and keep it shaded, which works nearly as well. Pot it up once roots are an inch (2 cm) long.
| Method | Best season | Time to establish | Notes |
|---|---|---|---|
| Rhizome division | Early spring or early autumn | 2 to 3 weeks to shoot | Fastest to a full plant, most fragments to manage |
| Stem cutting in water | Late spring to early summer | 1 to 2 weeks to root | Easy to watch, no soil to carry |
| Stem cutting in compost | Late spring to early summer | 2 to 3 weeks to root | Keep shaded and damp, do not let it dry |
| Layering a trailing stem | Any time in growth | 2 weeks at the node | Happens by accident; the usual escape route |
| Seed | Not worth attempting | Slow and variable | Variegated forms do not come true from seed |
The variegated form will not come true from seed and is only reliably increased by division or cuttings from a shoot that is still well colored.
Taking divisions from a variegated plant
If your plant is the cream and pink variegated form, choose the division material carefully or you will propagate the reversion. Plain green shoots grow from plain green sections of rhizome, and a division taken from that part of the clump gives you a plain green plant that runs harder than the colored one.
Follow a well-colored shoot down to the rhizome it comes from and take that section. Discard rhizome attached to plain green shoots rather than potting it up as a spare, because a spare pot of the green form is simply another source of escape. Even a careful division will throw some green shoots eventually, so plan to renew the pot from the best-colored material every two or three years.
Destroying what you do not want
Every division produces far more material than you need, and this is the point at which most gardens acquire their fish mint problem. Surplus rhizome does not die if you throw it on a heap, tuck it behind a shed or bury it at the bottom of a hole.
- Dry it to a crisp on a hard surface Spread the rhizomes in a single layer on paving or a metal tray in full sun for a week or more until they snap dry. Rhizome dried right through will not regrow.
- Or seal it in a bag until it breaks down Put the material in a heavy black bag, tie it shut and leave it in the sun for two or three months. Open it only when the contents are a brown liquid mass.
- Then put it in household waste Once fully dried or rotted it is safe for household waste. Do not use a green waste collection with live material, because it may spread through the compost produced.
- Never use a cool garden compost pile An ordinary heap does not get hot enough or stay hot for long enough. Rhizomes survive in it and you spread them across the whole garden with the finished compost.
- Check the ground where you worked Go back to the bench, path or tarpaulin two weeks later and look for shoots in cracks and joints. Fragments lodge in the smallest gaps and start there.
Write down the date of every division and how many pieces you kept. If a stray plant appears the following year, that record usually points straight at where the fragments were dropped.