How to grow Knotweed in the UK
Persicaria amplexicaulis
Knotweed (Persicaria amplexicaulis) is a flower that grows well in UK gardens. Long flowering — months of colour. 'Firetail' is reliable red. Don't confuse with invasive cousin. This guide covers when and how to sow Knotweed, the soil and position it likes, watering and feeding, companion planting, and when to harvest.
Type
Flowers
Difficulty
Easy — good for beginners
Position
partial sun (3–6 hrs)
Sow
spring
Harvest
—
When to sow & grow Knotweed
Sowing and harvest window through the year (UK):
Jan | Feb | Mar | Apr Plant | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
Soil, position & care
- Soil
- Fertile, moisture-retentive but free-draining soil
- Soil pH
- 6.0–7.5
- Position
- Sun or part shade depending on species
- Sowing depth
- Plant at the same depth as the pot
- Spacing
- 30–60 cm apart
- Sowing
- Plant container-grown stock spring or autumn; divide established clumps in spring
- Growing
- Water well the first season until established; mulch in spring
- Harvest & upkeep
- Cut back faded foliage in late autumn or early spring; divide every 3–4 years
- Watch for
- Slugs and snails on new shoots; otherwise robust
Companion planting for Knotweed
No specific companion notes for this plant.
Grow Knotweed this year
Add Knotweed to your free 12-month plan and get watering & sowing reminders — no sign-up needed.
Knotweed FAQs
How much sun does Knotweed need?
Knotweed prefers partial sun (3–6 hrs).
Is Knotweed easy to grow?
Easy — good for beginners. Long flowering — months of colour. 'Firetail' is reliable red. Don't confuse with invasive cousin.