Annual bedding
How to grow lobelia
Lobelia erinus
Bedding lobelia is sown on the surface of the compost in February or March at 18 to 21 °C, or bought as plugs in spring, and planted out in late May once frost has passed. It flowers from June to September in sun or part shade. Water is what decides success: it must never dry out, so it does best in baskets and pots that are watered daily. Shear it back by half if it browns in July.
- Hardiness
- Half-hardy annual
- Position
- Sun to part shade
- Soil
- Moist, fertile
- Ideal pH
- 6.0 to 7.0
- Water
- High, flags quickly if dry
- Feeding
- Light feeder
Sowing and planting lobelia
WhenSow Feb to Mar with heat or buy plugs; plant out late May; flowers Jun to Sep
Starting off
Sow Feb to Mar on the surface of moist compost at 18 to 21 °C, uncovered, as the seed is dust-fine; germination takes 14 to 21 days. Prick out in small clumps of 4 to 6 seedlings rather than singly, grow on at 13 °C and plant out after the last frost in late May.
Spacing and planting
Plant 10 to 15 cm apart in bedding or as plugs in baskets, five to seven per 35 cm basket; plant at plug depth. Best in a 25 cm pot or basket kept moist.
Varieties worth growing
- 'Crystal Palace'
- Compact bush type with deep blue flowers over bronze foliage; the classic edging lobelia.
- 'Cambridge Blue'
- Sky-blue flowers on a neat 10 cm mound with green leaves; pairs with 'Crystal Palace' for a two-tone edge.
- 'Mrs Clibran'
- Dark blue with a clear white eye, compact; good in window boxes where you see it close up.
- Cascade Series
- Trailing type for baskets, sold as a mix or as single colours including blue, white, lilac and red-purple; stems hang 30 cm or more.
- 'Sapphire'
- Trailing, violet-blue with a white eye; the one to buy if you want a single trailing variety.
Lobelia month by month
Timings are for central England. Allow two weeks later in the north and on cold, heavy soil.
- January
Order seed or plugs.
- February
Sow on the surface in a heated propagator at 18 to 21 °C if you have good light.
- March
Main sowing. Prick out earlier sowings in clumps of 4 to 6 seedlings.
- April
Grow on at 13 °C. Pot up bought plugs. Plant baskets under cover.
- May
Harden off. Plant out in the last week once frost has passed.
- June
Flowering starts. Water daily. Begin liquid feed four to six weeks after planting.
- July
Water baskets twice a day in heat. Shear back by half if plants brown, then feed.
- August
Second flush. Keep watering and feeding.
- September
Flowering tails off. Last feed early in the month.
- October
Pull out and compost after the first frost.
- November
Nothing to do.
- December
Nothing to do.
Feeding lobelia
A light feeder. Fresh compost carries it for the first month or more; after that a weak liquid feed once a fortnight keeps a basket flowering. In a border it needs nothing but moisture.
Light, a weak high-K feed in baskets sustains flowering.
Feeding plan
Planting, late May
No feed
None. Fresh multipurpose compost holds enough for four to six weeks.
From late June to early September, baskets and pots, every 2 weeks
3 ml per litre of water, the bottom of the label range: 15 ml in a 5 litre can. Give a 35 cm basket about 1 litre in place of a plain watering.
July, straight after shearing back
1 g per litre of water as a drench, once, then go back to the fortnightly liquid feed.
Bedding in the ground
Garden compost
A 3 cm layer forked in before planting to hold moisture. No fertiliser.
Signs to watch
Pale leaves and thin flowering in a basket
Nitrogen washed out
A balanced liquid feed fortnightly
Browning and die-back in Jul
Heat and dry roots
Water twice daily and shear back
Lush green and little blue
Too much nitrogen
Switch to high-potash
Pests, diseases and problems
Seedlings collapse in patches at compost level, with a fluffy mould
Damping off, encouraged by thick sowing, overwatering and stale air
Use new compost and clean trays, sow thinly, water from below with tap water, and ventilate as soon as seedlings show. Prick out early in small clumps.
Seedlings pale, thin and stretched
Too little light for a February sowing on a windowsill
Sow in March instead if you have no grow light, turn the tray daily and grow on cooler, at about 13 °C, once pricked out.
Young plants sit still, turn purple-bronze and rot at the base after planting
Planted out too early into cold, wet compost
Harden off for 10 days and hold back until late May. Replace losses with plugs; they catch up fast in warmth.
Grey fluffy mould in the centre of a crowded basket in wet weather
Grey mould (botrytis) on dead flowers and stems
Shear off the affected growth, clear the debris out of the basket, and water the compost in the morning, not the foliage.
Pruning
Pruning and care
No deadheading needed. When plants tire and brown in Jul, shear back by half, water and feed, and a second flush follows in 3 weeks. No staking; it dies at the first frost, so compost it in Oct.
Good to knowTrailing and bush types; trim mid-season if it tires.
Growing lobelia in pots
This is first and last a container plant. Use trailing types for baskets, five to seven plugs round the edge of a 35 cm basket, and bush types for pots and window boxes at 10 to 15 cm apart. A peat-free multipurpose compost with good water-holding is right; lobelia has fine, shallow roots and a basket that dries out once in July may not recover. Water every day from June and twice on hot, windy days, until it runs from the base. A spot with afternoon shade keeps it flowering longer than full sun on a south wall.
Lobelia: common questions
Why has my lobelia gone brown and stopped flowering?
It has almost certainly dried out or overheated, usually in a basket in July. Shear the plant back by half, soak the compost thoroughly, give one feed, and move the container out of afternoon sun if you can. New growth and flowers follow in about three weeks.
Does lobelia come back every year?
No, not bedding lobelia. Lobelia erinus is a tender perennial grown as a half-hardy annual in the UK and is killed by the first frost, so it is sown or bought fresh each spring. The tall border lobelias, such as Lobelia cardinalis, are different plants and are perennial.
Will lobelia grow in shade?
Yes, it flowers well in part shade and is one of the better bedding plants for a north or east-facing basket. In deep shade it grows leggy with few flowers. In full sun it needs more water to keep going through July and August.
Sources
Growing information on this page was checked against these references in November 2026. Feeding rates are Dr Forest label rates.
- How to grow lobeliaBBC Gardeners' World Magazine