I am very aware that veg have taken a back seat on here lately and I will remedy that next week but for now another ornamental. Persicaria campanulata (formerly Polygonum campanulatum) is a plant I have known for a long time. I first made its acquaintance when I was at school and had a Sunday morning gardening job. In that garden it grew in deep shade under trees and, although a bit spindly, survived in the dry shade and provided pleasant late summer colour in the same palette as Japanese anemones. Being a knotweed it can look after itself in most gardens and is a vigorous plant. It has the characteristic, zigzag stems and lance-shaped leaves and small flowers.

The clump here was planted last spring and is now at least 1m high and getting on for 2m across. It is more or less evergreen but in winter is a low clump of foliage. You should cut down the stems to the base in autumn to best appreciate the winter effect. It then rises, like a lump of dough, throughout spring until it flows over the edge of the bowl and forms an ever-increasing mass of leaves and, from July till the frosts, a cloud of flowers. The individual flowers are small and open pink and fade to white or vice versa (I haven’t checked which to be totally honest – another job for later today).

The leaves are greyish and beautiful in themselves, being heavily veined. It is a native to the Himalaya but is obviously naturalised in Ireland (and the UK) and is referred to as ‘lesser knotweed’ here. That seems an odd name since it is one of the bigger knotweeds and while ‘lesser’ can also refer to flowers or medicinal use I don’t think there is anything lesser about this unless you compare it to Russian vine! It is also known as the bell-flowered knotweed which makes a bit more sense.

While the growth of the plant from these photos may intimidate you I don’t think this could ever be a problem but it is a large plant. I intend to divide it in spring and plant it in lots of shady places where it will usefully swamp out weeds. In theory it should prefer damp shade but I find it will put up with some drought when established. Here it is planted on the north side of a wall where it gets some sun in summer when the sun is high but none later in the year. The soil is clay and quite moist which will explain the vigour of the plant – well that and a good mulch of manure.

Despite the rich conditions it has not really flopped. The stems are good and stiff and although the clump is wide it has not collapsed in the centre.

In the past I have grown ‘Rosenrot’ which has deeper pink flowers and there is a white form (‘Alba’) which would be nice too. When it comes to companions I would like to try white Japanese anemones and maybe something purple or blue like Strobilanthes attenuata (which comes from a similar part of the world) or maybe a vigorous aster. Alternatively plant it with something that has good autumn colour. I am putting some under some Japanese acers for next year and I look forward to seeing the fallen scarlet acer leaves dropping on the greyish leaves and pink blooms – in fact I may collect some later to see how it looks!

Geoff’s rating 8/10

Garden rating 8/10

bellflowered knotweed, lesser knotweed, persicaria campanulata, persicaria rosenrot, polygonum campanulatum, polygonum rosenrot, strobilathes attenuata