Japanese anemones are genuinely beautiful plants. From August through to October, when much of the garden is beginning to wind down, they carry delicate pink or white flowers on tall, wiry stems above bold foliage, and they do this in shade and partial shade where few other plants perform as well at that time of year. I understand entirely why people buy them. They look lovely in the garden centre. They look lovely in the garden the first season, and the second. The problem comes in the third, fourth and fifth years, and every year after that, when you understand what you have actually introduced into your soil. Japanese anemones, specifically the autumn-flowering forms Anemone hupehensis and Anemone x hybrida, are among the most aggressively spreading perennials available in Irish garden centres, and I do not recommend planting them.

The mechanism of their spread is underground. They travel through the soil on rhizomes, fine root-like structures that extend outward from the parent plant and produce new shoots wherever they find space. Those new plants produce their own rhizomes, and so on, year after year. In an Irish garden with its rich, moist soil and relatively mild winters, the conditions for this kind of spread are close to ideal. A single plant bought in a pot will, within a few years, have colonised a significant area. It will grow through the roots of neighbouring plants, push up between paving, travel under paths and emerge on the other side, and find its way into any corner of the garden where the soil is workable. The roots are shallow enough that it can establish almost anywhere. The difficulty of removal compounds the problem: any fragment of root left in the ground after digging will produce a new plant. And there will always be fragments.

The flowers are undeniably beautiful. This is precisely the problem. Japanese anemones look entirely innocent at the point of purchase and for the first season or two after planting.

I have direct experience of this. I had a large area of my own garden colonised by Japanese anemone, and I want to tell you what I did to deal with it because it is the approach I would recommend to anyone in the same situation. I did not use chemicals. I do not recommend chemical herbicides for this kind of problem, both because of the ecological impact on the soil biology and the wider garden environment, and because in my experience the results with deeply rhizomatous plants are inconsistent at best. What I used instead was smothering, and it worked.

The key details of that approach are worth being precise about. The fabric must be compostable, not plastic. A plastic weed membrane will do the smothering job initially, but over time it compacts the soil beneath it, destroys the biological activity in the soil, and creates more problems than it solves. Wet cardboard laid directly over the area is an excellent alternative to compostable fabric, or can be used in combination with it. Both will break down over time and integrate into the soil without causing harm. The depth of material on top matters: twelve inches gives the plants you are putting in a genuine growing medium above the suppression layer, and the weight of it sustains the smothering effect below. When planting into this layer, be careful not to cut or pierce the fabric beneath. Any gap gives the anemone rhizomes below an escape route, and they will find it. Three years on, the approach has held, and the garden in that area is performing exactly as intended.

If the infestation is less established, regular removal of new shoots as they appear through the growing season, combined with persistent digging to remove as much of the root system as possible in one thorough initial session, can be effective over two to three years. The critical discipline is not to dig repeatedly after the first clearance: disturbing the soil multiple times breaks the rhizomes into smaller pieces and spreads the problem rather than reducing it. One thorough dig, then hand-pulling of any regrowth, is the right sequence.

Anemones worth growing in Irish gardens

The autumn-flowering Japanese anemone is not representative of the genus as a whole, and I want to be clear about that because it would be a shame to avoid all anemones on the basis of one problematic group. The spring-flowering forms are an entirely different proposition: well-behaved, genuinely beautiful, and in the case of the wood anemone, native to Ireland.

The spring-flowering bulb anemones are a completely different plant in terms of habit. They naturalise gently and never become the management problem that Japanese anemones create.

Anemone nemorosa, the wood anemone, is a native Irish wildflower. It grows in deciduous woodland across most of Ireland, forming low carpets of delicate white flowers in March and April before the tree canopy closes over. In the garden it is well-suited to the base of deciduous trees and shrubs, naturalising slowly and gently without becoming a problem. It does spread through rhizomes but at a pace that is manageable and appropriate for a woodland setting, and unlike the Japanese forms it is supporting native ecology rather than competing with it. The blue-flowered forms, produced as garden selections of the species, are among the most beautiful small spring plants you can grow in an Irish garden.

The blue-flowered form of Anemone nemorosa, our native wood anemone. A beautiful, well-behaved spring plant that naturalises gently at the base of deciduous trees and shrubs.

Anemone blanda is the other spring-flowering anemone commonly available in Irish garden centres, sold as small corms in autumn alongside other spring bulbs. It is not native to Ireland or Britain, originating from southeastern Europe and Turkey, but it is a well-behaved garden plant that naturalises without becoming problematic. It produces a low carpet of daisy-like flowers in blue, pink and white from February to April, performing particularly well at the base of deciduous trees where it receives good light in early spring before the leaves emerge. It requires well-drained soil and dislikes sitting wet over winter, which means it suits lighter soils better than the heavier clay that much of Ireland has. In the right conditions it is charming and entirely manageable.

Anemone blanda flowering in early spring. Not native to Ireland, but a well-behaved garden plant that naturalises without spreading aggressively. Needs good drainage and a dry summer dormancy.

The variety I would single out for special mention is Anemone Wild Swan. This is a relatively recent introduction that represents something genuinely new in the genus. It flowers intermittently from May right through to November, producing large white flowers on stems around forty to fifty centimetres tall, with a distinctive blue-grey streak on the reverse of each petal that gives the buds an unusual, almost luminous quality. It is not invasive. It does not spread aggressively. It is a clump-forming perennial that behaves itself in a mixed border, and the flowering season it provides, bridging spring, summer and autumn, makes it one of the most useful perennials available to Irish gardeners. The reverse of the petals is as beautiful as the front, which is rare in any plant.

Anemone Wild Swan in flower. The long season, from May to November, and the non-invasive habit make this one of the most useful perennials for Irish gardens. A beautiful plant that behaves itself.

The reverse of the Anemone Wild Swan petals. The blue-grey streak that marks each petal on the underside gives the buds a quality that is unusual in any flowering plant.

The underlying principle across all of this is the same one that governs every planting decision worth making: the right plant in the right place, understood properly before it goes in the ground. Japanese anemones are not bad plants in any absolute sense. In a large, wild, unmanaged area where spreading is not a problem, they can be extraordinary in flower. In a managed garden, planted among other things you value and want to keep, they will eventually become a management problem that costs you more effort to deal with than any amount of autumn colour is worth. The spring-flowering anemones and Anemone Wild Swan give you beauty from this genus without that cost. That is the straightforward advice: avoid the Japanese forms in a managed garden, and grow the spring ones and Wild Swan instead. The soil these plants go into matters too. A well-structured, biologically active soil gives any perennial the foundation it needs to establish well and perform consistently year after year.