Japanese Anemone After Flowering: Deadheading, Seed Heads and Cutting Back

Flowering ends when the weather ends it

Most perennials finish flowering and then have a long, visible tail end to the season. Japanese anemone does not really do that. It opens its first flowers in late summer and keeps opening more, from buds that form successively along each branched stem, until a hard frost stops it. In a mild autumn it can still be producing fresh flowers weeks after everything else in the border has gone over.

So there is no single moment at which the plant is finished and you tidy it. What you get instead is a long overlap, several weeks in which the same stem carries open flowers, tight round felted buds and spent flowers turning into seed heads all at once. Cutting a stem back because part of it is over throws away the buds further along it.

The practical rule that follows from this is: work on individual flowers while the plant is still going, and leave stem removal until the plant has actually stopped.

Deadheading while it is still in flower

Deadheading Japanese anemone does not make it flower for longer. The stems carry a set number of buds, and removing spent flowers does not persuade them to make more. It is a cosmetic job, done because the browning flowers sit right beside the fresh ones and dull the whole display.

Because of that, keep it light and keep it precise. Take off the individual spent flower, not the stem it is on.

1. Follow the spent flower back to its own junction Each flower sits on a short side branch that joins the main stem at a fork. Trace it back to that fork and cut just above it. The rest of the stem, and all the unopened buds on it, carry on as normal.
2. Do not cut the main stem back Shortening a main stem removes every bud above the cut. On a plant whose whole value is a long succession of flowers, that is an expensive mistake, and it is the usual reason someone reports that their anemone stopped flowering early.
3. Do it in one pass a week Ten minutes once a week through the flowering season keeps the clump looking fresh. Chasing individual flowers daily is not worth the time, and the plant does not care either way.
4. Stop deadheading in mid autumn Once the display is clearly winding down, leave the last flowers to form seed heads. The cottony heads catch low autumn light and hold their shape for weeks, and they are one of the better things this plant does.

Seed heads: leave them or lose them

After the petal-like sepals drop, each flower leaves a green button that swells, dries and then bursts into a ball of white cottony fluff carrying the seed. On a mature colony there will be hundreds of these, and they are genuinely ornamental through late autumn and into winter.

Self-seeding is worth knowing about but is not what makes this plant spread. Many garden forms set little viable seed, and the seedlings that do appear are slow and easily hoed off. The colony expands underground, through horizontal roots, and leaving the seed heads on does not measurably speed that up. If you like the look of them, keep them.

The reasons to remove them are practical rather than horticultural. The fluff blows about and sticks to everything nearby, and in a small paved garden it becomes a nuisance. And if you have any interest in raising plants from seed, you need to collect the heads just as they start to open rather than after the wind has taken them.

Cutting back, and how late is too late

Cut the flower stems down after frost has blackened them, not before. Cut them to about two inches (5 cm) above the ground with pruners or shears. The basal leaves are a separate matter: leave them as long as they are green, because they are still feeding the crown for the following spring, and remove them only once they have gone yellow and limp.

There is a real choice about timing. Cutting everything down in autumn gives you a clean bed and removes shelter for slugs, which will be feeding on the new shoots come spring. Leaving the stems and seed heads standing until late winter gives you winter structure, some shelter for the crown in cold gardens, and seed for birds. Both are defensible. In a cold garden with wet winters, leaning toward leaving them up and cutting in late winter is the safer option, because the dead growth protects the crown.

What is not a good idea is cutting the whole plant to the ground in late summer while it is still growing, in the hope of a second flush. It will not reflower, and you will have removed the display for that year.

Clear the cut material away rather than leaving it lying on the crown. A mat of wet stems sitting over a dormant crown all winter is one of the few things that actually kills this plant.

If any of the foliage showed dark wedge-shaped patches between the veins during the season, bag that material and dispose of it rather than composting it. That pattern indicates foliar nematodes, which survive in fallen leaf debris and re-infect the new growth in spring.

What to record before the stems go

Before you cut anything down, write down the date the last flower faded, and the height the stems actually reached. Both change with the season and with the age of the clump, and both are what you need when you are deciding next spring whether to put support in and how tall to set it.

Note as well whether the clump splayed outward or held itself upright, and if it splayed, in which direction. Almost always it goes away from the prevailing wind or toward the light, and once you know which way a particular clump falls you can put the support on that side and stop it happening.

Finally, mark where the outermost shoots came up this year, with a cane or a note measured from a fixed point. In early spring the bed will look empty and you will not remember, and the first job of the year is deciding where the colony is allowed to be.