How to Propagate Japanese Anemone: Root Cuttings, Division and Offsets

Root cuttings, not division, are the reliable method

Japanese anemone spreads naturally by sending horizontal roots out through the soil and pushing up new shoots along them. That means the roots themselves are capable of making whole new plants, which is exactly what a root cutting exploits. It is the reason a plant is so hard to eradicate, and it is also the reason it is one of the easiest perennials in the garden to increase.

Division works too, but less well than you would expect. The crown is woody and the plant resents having its roots disturbed, so divided pieces often sulk for a whole season before they get going, in the same way a newly bought plant does. Root cuttings, taken while the plant is dormant and therefore not disturbed at all in its growing season, are quicker and more certain.

Whichever method you use, do the work in the dormant season. This is not a plant to lift and split while it is in growth.

Taking root cuttings

Do this in the dormant season, any time from after the stems die down until growth restarts in late winter. You need very little material. A handful of root pieces from one plant will give you a dozen new plants, which is far more than most gardens need, so take from one side of the clump only and leave the rest undisturbed.

1. Expose roots on one side of the clump Scrape the soil away from one side of an established plant with a hand fork until you can see the roots running out horizontally. You do not need to lift the whole plant. The horizontal running roots, roughly the thickness of a pencil, are the ones you want.
2. Cut lengths of two to three inches (5 to 8 cm) Take several. Cut the end nearest the parent plant square across and the far end at a slant. That way you can tell at a glance which end was uppermost when you come to plant them, which matters because a cutting planted upside down will not grow.
3. Insert them the right way up Fill pots or a deep tray with gritty, free-draining compost. Push each cutting in vertically, square end uppermost, until the top is level with the surface. Cover with a quarter inch (5 mm) of grit or compost. Thin roots can instead be laid flat on the surface and covered.
4. Keep them cool, barely moist and unheated Stand them in a cold frame, unheated greenhouse or sheltered spot outdoors. They do not need warmth and they rot in wet compost. Do not water again until you see shoots. This is where most root cuttings are lost.
5. Wait for shoots, then wait longer Shoots appear in spring, usually within eight to twelve weeks. A shoot means nothing until roots follow, so resist potting up the moment you see green. Wait until roots show at the drainage holes, then pot each cutting individually.
6. Grow on for a full season before planting out Keep the young plants in pots through their first summer, watering regularly, and plant them out in autumn or the following spring. Planted straight into a border as tiny plants they are easily lost to slugs and drought.

Because every root fragment can grow, be careful where you tip the leftovers. Trimmings emptied onto a compost pile or a spare corner will produce plants there. Bag anything you are not deliberately propagating.

Dividing an established clump

Divide in early spring, just as the new shoots break the surface, so you can see what you are cutting and the plant has the whole season ahead of it to recover. Autumn division works in mild gardens with free-draining soil but risks losses where winters are wet.

Lift the clump with a fork, taking as wide a rootball as you can manage, and shake or wash off enough soil to see the structure. The crown is tough and woody, so pulling it apart by hand rarely works. Cut it into pieces with a spade or an old knife, making sure each piece has at least one visible growing shoot and a decent length of root attached. Pieces roughly the size of a fist establish fastest; very small fragments will grow but take an extra year.

Replant immediately at the same depth the plant was growing before, water in thoroughly, and keep the divisions watered right through their first summer. Expect them to look unimpressive that year and to flower properly in their second. A division that produces leaves and no flowers in year one has not failed.

There is rarely a horticultural need to divide this plant for its own sake. It does not decline in the way many perennials do, and a colony can sit happily for a decade. Divide when you want more plants, or when you are reducing the size of a colony anyway.

Lifting rooted offsets, the method that costs nothing

The easiest propagation of all is simply to use the plants the colony is already making for you. Every spring, new leaf rosettes appear a foot (30 cm) or more out from the parent clump, each one sitting on a horizontal root and each one already rooted into the soil where it stands.

These are complete young plants. In early spring, push a hand fork under one, lift it with a few inches of the connecting root still attached, and sever the root on the parent side. Pot it or replant it straight away and keep it watered. It will usually flower in its second season.

This is the same operation as the annual edge cut that keeps a colony in bounds, so you get the plants for free from work you were doing anyway. It also means there is almost never a reason to buy a second plant of this species: within three years the first one supplies all you need.

Seed, and what to write down

Seed is possible but is the least useful route. Many garden forms set poor seed, the fluffy heads make it awkward to collect, germination is slow and uneven, and the seedlings vary. Plants from seed take three years or more to reach flowering size, against two from a root cutting.

If you want to try it, collect the heads just as the white fluff begins to loosen, rub the seed free of the down, and sow it fresh in autumn in pots stood outside. Cold winter temperatures break dormancy and germination follows in spring. Do not sow into a heated propagator; warmth without a cold period gives nothing.

Keep a short record of anything you propagate: the date, the method, and where the parent plant was. Root cuttings sitting in a tray in a cold frame are indistinguishable from bare compost for two months, and a labeled note of when you took them is what stops you throwing them out or watering them to death. Note the date shoots first appeared as well, because on a second attempt it tells you immediately whether a batch is late or dead.