When to plant and prune Border phlox
Border phlox flowers from late June to late August and the dates below cover planting, flowering and the pruning window.
Planting, flowering and pruning by region
Border phlox is grown to the calendar rather than to the frost, so the same dates apply across the whole UK and every region below reads the same. Where a plant’s timings do follow the frost, Plot shifts them from the Midlands and Lowland Wales baseline using Met Office average frost dates.
| Where you are | Plant | In flower | Prune |
|---|---|---|---|
| South West Coast and Cornwall | late March to mid May | late June to late August | early February to early March |
| South Coast and Channel | late March to mid May | late June to late August | early February to early March |
| Greater London (Urban Heat Island) | late March to mid May | late June to late August | early February to early March |
| South East and Home Counties | late March to mid May | late June to late August | early February to early March |
| East Anglia | late March to mid May | late June to late August | early February to early March |
| Midlands and Lowland Wales | late March to mid May | late June to late August | early February to early March |
| Wales and West Coast | late March to mid May | late June to late August | early February to early March |
| Northern England | late March to mid May | late June to late August | early February to early March |
| Scotland Lowlands and Central Belt | late March to mid May | late June to late August | early February to early March |
| Scotland Highlands and Islands | late March to mid May | late June to late August | early February to early March |
| Northern Ireland | late March to mid May | late June to late August | early February to early March |
| Channel Islands and Isle of Man | late March to mid May | late June to late August | early February to early March |
Growing notes
It must not dry out — drought is what brings on the powdery mildew that phlox is blamed for. The Chelsea chop (cutting stems back by up to half in late May) gives shorter plants and delays flowering by three or four weeks.
At a glance
- Spacing
- 60 cm between plants
- Eventual height
- 110 cm
- Eventual spread
- 60 cm
- Hardiness
- H7
- Sun
- Full
- Frost tender
- No
- Grows in a container
- Yes, 20 litres or more
- Balcony rating
- 3 out of 5
Feeding
Spring mulch of organic matter, especially important on light, sandy soils.
Pruning group
Cut the old stems back to the base in late winter or early spring.
Bare-root season
Bare-root stock is lifted and sold while dormant, from early November to late February. Container-grown plants can go in at other times of year, but bare-root is cheaper and establishes well.
What usually goes wrong
- powdery mildew in dry soil
- phlox eelworm
- slugs and snails
Related guides
Timings cross-checked against RHS guidance for border phlox.