Gadenin日本語Get the appDivision serves two purposes at once
A clump of ayame iris expands outward from its original rhizome, leaving the oldest sections in the middle to go woody and stop producing. After three or four years the center is dead weight and the flowering ring has moved to the edge. Dividing solves that and gives you new plants at the same time, which is why it is the standard method of increase for this iris rather than a last resort.
Do not wait for the clump to look bad. A clump divided on schedule barely misses a season, while one left until the center has collapsed and the outer rhizomes are congested and half rotten will take two or three years to come back. Three to four years is the interval; mark it in your notes the day you plant.
Each viable division needs one healthy rhizome section three to four inches (8 to 10 cm) long with at least one leaf fan and a good spread of live roots. A section with no fan will not grow, and a fan with no firm rhizome behind it has nothing to live on.
When to do it
There are two good windows and one bad one. The best is the few weeks just after flowering finishes, when the plant is actively rooting and the weather is warm. The second is early autumn, at least six weeks before the ground freezes, which gives roots time to anchor before winter. Dividing in the middle of a hot dry summer or into cold wet ground in late autumn loses plants.
| Window | How it goes | Notes |
|---|---|---|
| Just after flowering | Best. Fast rooting, minimal check | Water through dry weather until new growth is clear |
| Early autumn | Good. Roots settle before frost | Allow 6 weeks of workable ground before the freeze |
| Midsummer heat | Poor. Divisions stall and dehydrate | Wait for cooler weather |
| Spring, as growth breaks | Possible but costs the flowers | Only if the clump is failing and cannot wait |
| Late autumn or winter | Bad. Rhizomes rot before rooting | Do not attempt |
Dividing a clump, step by step
Work on a dry day with clean tools. A rhizome cut with a dirty blade is an open invitation to soft rot, and the pathogen travels from plant to plant on the knife. Wipe the blade between clumps.
- Cut the foliage back first Trim the leaf fans to six inches (15 cm) in a shallow inverted V. This is the one time cutting foliage is correct: it reduces water loss while the roots are damaged, and it lets you see what you are doing. Discard the trimmings rather than leaving them on the bed.
- Lift the whole clump Push a fork in well outside the leaf spread, all the way around, and lever the clump up whole. The rhizomes are shallow and brittle, so lift rather than pull. Shake and hose off enough soil to see the structure clearly.
- Break it into young sections Snap or cut the clump so each piece has one to two fans and a firm rhizome section three to four inches (8 to 10 cm) long with live roots. Healthy rhizome is firm and pale inside. Anything soft, hollow, foul-smelling or discolored goes in the trash, not the compost pile.
- Throw away the old center The woody leafless middle section will never flower again. Keeping it out of sentiment simply reintroduces the crowding you just fixed. Discard it and replant only the vigorous outer pieces.
- Let the cuts dry, then replant shallow Leave the divisions in a shaded airy spot for a few hours until the cut surfaces have dried and sealed. Then replant with the rhizome top at or barely below the surface, fans pointing outward, twelve inches (30 cm) apart. Water once to settle, then let the surface dry between waterings.
Never compost rhizome sections that are soft or smell sour. Bacterial soft rot survives in the heap and comes straight back on the next load of compost. Bag them and put them out with household waste.
Growing ayame iris from seed
Seed works but it is slow and the results vary, because seedlings do not come true to their parent. It is worth doing when you want a large number of plants for a drift and do not mind variation in flower shade, or simply want to see what turns up.
Let a few pods form on strong stems and collect them when they turn brown and begin to split. Seed of this iris needs a cold period to break dormancy: sow into pots of gritty free-draining mix in autumn and leave them outdoors over winter, or give the seed eight to ten weeks in damp sand in a refrigerator and sow in spring. Germination is uneven and can straggle over two seasons, so do not throw the pot out after one blank spring.
Grow seedlings on in pots for their first full year, then plant them out at the same shallow depth as divisions. Expect the first flowers in the second or third year from sowing. Along the way, remove seedlings that appear in the border by themselves unless you want them, because self-sown plants crowd the parent clump and shift the flowering ring.
Keep a division record
Write down the date you divided, how many usable divisions each clump gave, where each one went, and how many looked rotten and were discarded. The count of discards is the useful number, because a rising proportion of soft rhizome from the same bed means that bed drains worse than you thought.
Note the year of division against each planting position too. Three or four years later, that single figure tells you which clumps are due without having to dig anything up to check.