Perennial
How to grow penstemons
Penstemon hybrids
Plant penstemons in April or May in full sun and soil that drains freely in winter, 45 to 60 cm apart. They flower from June to October if you deadhead. Two things decide whether they come back: winter wet at the roots, which kills more plants than cold, and leaving the old stems on until April to protect the crown. Take a few cuttings each August, because even well-grown plants tire after three or four years.
- Hardiness
- Frost-hardy; leave stems on over winter
- Position
- Full sun
- Soil
- Fertile, free-draining
- Ideal pH
- 6.0 to 7.5
- Water
- Low to moderate
- Feeding
- Moderate feeder
Sowing and planting penstemons
WhenPlant Apr to May; flowers Jun to Oct; cut back Apr
Starting off
Plant pot-grown plants Apr to May so they establish before winter. Semi-ripe cuttings 8 to 10 cm long in Aug to Sep, rooted in gritty compost at 18 °C in 3 to 4 weeks and overwintered in a cold frame, are the insurance against loss; renew plants every 3 to 4 years. Seed sown Feb to Mar at 15 to 18 °C germinates in 14 to 21 days but varies.
Spacing and planting
Plant 45 to 60 cm apart in groups of three; plant at pot depth with grit on clay. Fine in a 30 cm pot of loam-based gritty compost, moved against a wall in winter.
Varieties worth growing
- 'Andenken an Friedrich Hahn' (sold as 'Garnet')
- Narrow-leaved, wine-red and the most reliably hardy border penstemon; the one to start with on cold or heavy ground.
- 'Hidcote Pink'
- Soft pink with a streaked throat, bushy and free-flowering, and nearly as tough as 'Garnet'.
- 'Sour Grapes'
- Large bells in a metallic mix of violet and blue; wider leaves, so give it a sheltered spot.
- 'Raven'
- Very dark purple with a white throat, about 1 m tall; strong upright spikes for the middle of a border.
- 'Alice Hindley'
- Tall, pale mauve and white, up to 1.2 m; elegant against a warm wall where the large flowers are protected.
Penstemons month by month
Timings are for central England. Allow two weeks later in the north and on cold, heavy soil.
- January
Nothing to do. Leave every stem standing.
- February
Sow seed in a heated propagator if you want to try it. Check pots are not sitting in water.
- March
Hold off pruning. Look for new shoots at the base and pot on overwintered cuttings.
- April
Cut back to 10 to 15 cm above the new basal shoots once hard frosts ease. Light feed. Start planting.
- May
Plant pot-grown plants and last year's cuttings. Watch for slugs on new growth.
- June
First spikes open. Deadhead to a side shoot as each one fades. Second and last light feed for pots early in the month.
- July
Keep deadheading. Water deeply once a week in drought.
- August
Take 8 to 10 cm cuttings from non-flowering side shoots.
- September
Last cuttings early in the month. Carry on deadheading while flowers come.
- October
Stop deadheading and leave the top growth on. Move rooted cuttings to a cold frame.
- November
Mulch round the crown with bark. Move pots against a house wall.
- December
Nothing to do. Do not tidy the stems.
Feeding penstemons
A light feeder. One modest feed after the April cut-back is enough in the ground; rich feeding gives soft, leafy growth that flops and suffers more in winter.
Moderate, a light potassium-leaning feed; sharp drainage matters more.
Feeding plan
April, after cutting back, beds
50 g/m², half the label rate of about 100 g/m². At 50 cm spacing each plant covers roughly 0.25 m², so that is about 12 g, a level tablespoon, scattered round each plant and watered in. Once only.
April, pots
2 g per litre of compost, the low end of the label top-dress: about 24 g for a 30 cm pot holding 12 litres, scratched into the surface and watered in.
Early June, pots only
The same 2 g per litre again: about 24 g for a 30 cm pot holding 12 litres, scratched into the surface and watered in, at least 5 to 6 weeks after the April dressing. Once. Nothing after June, so growth firms up before winter.
Signs to watch
Leaves yellow and the plant collapses in Feb
Winter wet rot, not nutrition
Gritty, raised soil
Lush, floppy growth with few spikes
Nitrogen excess
High-potash only
Small flowers and brown leaf edges in Aug
Dry roots and potash short
Water and a high-potash feed
Pests, diseases and problems
New basal shoots grazed off or shredded in April and May
Slugs and snails sheltering in the old stems and mulch
Check under the crown when you cut back, pull bark mulch a few centimetres away from the new shoots, go out with a torch on damp evenings, and use nematodes once the soil is above 5 °C.
Brown or black patches on the leaves, sharply bounded by the veins, moving up the plant from the base
Leaf and bud eelworm, spread in the film of water on wet foliage
Remove and bin affected plants rather than composting them, do not take cuttings from them, and replant with clean stock in a different spot.
White powdery coating on leaves in late summer
Powdery mildew on plants that are dry at the root
Soak the roots once a week in dry spells, thin congested stems for air, and pick off the worst leaves.
Shoot tips sticky and curled, clusters of green insects under the buds
Aphids
Rub them off with finger and thumb or knock them off with a jet of water; ladybirds and hoverflies usually catch up by June.
Plant woody and bare at the base with fewer, shorter spikes each year
Age: penstemons are short-lived and decline after three or four years
Replace with plants raised from cuttings taken in August or September; hard pruning an old plant rarely revives it.
Pruning
Pruning and care
Deadhead spent spikes to a side shoot through Jun to Oct. Leave all stems on over winter to shield the crown, then cut back to 10 to 15 cm just above new basal shoots in Apr, never in autumn. No staking. Mulch the crown 5 cm with bark in Nov; narrow-leaved varieties such as 'Garnet' are the hardiest, large-flowered ones need a sheltered wall.
Good to knowDon't cut back until spring (old growth protects the crown over winter); deadhead for a long show.
Growing penstemons in pots
Penstemons do well in a 30 cm pot, which holds about 12 litres, filled with loam-based compost and a quarter by volume of grit. The pot must drain freely: raise it on feet from October so winter rain runs straight through. Water when the top few centimetres are dry in summer, which may be every other day in July, and barely at all in winter. Move the pot against a house wall from November, where it is drier and a degree or two warmer. Repot into fresh compost every second April, or better, start again with a rooted cutting.
Penstemons: common questions
When should I cut back penstemons?
Cut penstemons back in April, not autumn. Wait until new shoots show at the base and the hardest frosts have passed, then cut the old stems to 10 to 15 cm, just above the new growth. The old top growth shields the crown through winter, and plants cut down in autumn are the ones most often lost.
Are penstemons hardy in the UK?
Most border penstemons are frost-hardy rather than fully hardy, surviving a normal winter in well-drained soil but not a cold, wet one. Narrow-leaved varieties such as 'Garnet' and 'Hidcote Pink' are the toughest; large-flowered, broad-leaved ones need a sheltered wall. Good drainage and a bark mulch over the crown matter more than fleece.
How do I take penstemon cuttings?
Take 8 to 10 cm cuttings from non-flowering side shoots in August or September. Trim below a leaf joint, strip the lower leaves, and push them round the edge of a pot of gritty compost. Kept shaded and just moist they root in three to four weeks; overwinter them in a cold frame and plant out in May.
Sources
Growing information on this page was checked against these references in November 2026. Feeding rates are Dr Forest label rates.