Plant of the Month: September – Persicaria affinis (knot weed)

The Persicaria, patches of which can be found at Culpeper now, comes into its own flowering in late summer to autumn when it is especially appreciated by the bees. It is a plant with a carefree and cosmopolitan character and appears virtually world wide in various forms. Native to Afghanistan, Nepal and India, China and Tibet, it typically grows in the mountains up to 4,000 ft. . The celebrated Victorian botanist, Sir Joseph Hooker, came across it in the Himalayas where he described it as ‘hanging in rosy clumps from moist precipices’.

It was formerly known as Polygonum, from the Polygonaceae family, which translates from the Greek as ‘many knees’ relating to the numerous joints in the fleshy stems. It’s a hardy creeping mat-forming perennial, making good ground cover. It needs little care though it likes moisture with good drainage and can go dormant on dry ground. The flowers eventually turn into tiny three-angled nuts.

It is described as ‘semi-evergreen’ as, with the frost, the heavily-veined, narrow elliptic leaves take on autumn colour and mostly stay on the plant through winter . New, green growth will appear in spring and the dainty pink or red flower spikes, depending on variety,

Whereas the common knotweed can be invasive, many of the cultivars make lovely trouble-free garden plants. Both Persicaria affinis ‘Superba’, which has pale pink flowers that deepen into claret red, and ‘Donald Lowndes’ where the pale flowers darken into russet tones, are recommended by the RHS and have an Award of Garden Merit.

Caroline Foley