How to Grow Lobelia
Lobelia At a Glance
Difficulty
Easy
Category
Flower
Sun Exposure
Partial Shade
Frost Tolerance
Frost Tender
Cold Hardiness
Survives to 2°C
Plant Family
Campanulaceae
Growing Season
Cool Season
Plant Lifecycle
Annual
How to Start It
★ Recommended for beginners
Lobelia seed is as fine as dust and slow to grow, so most people start with small plants from a garden centre in spring. Plant them out about 1 week after your last frost, 15 cm apart, without pulling the little clumps apart.
Lobelia makes clouds of tiny flowers, often a deep true blue, that spill over the edges of pots and baskets all summer. It likes cool weather and can stop blooming in a heat wave, but a trim and a drink usually bring it back.
When To Start
Lobelia likes cool weather. Sow it in early spring, as soon as the ground can be worked.
We do not have exact sowing dates for this one yet.
When should you plant Lobelia?
Your planting dates depend on your local climate. Sign up and add your location to unlock personalized dates.
Your Lobelia Planting Window
Start planting
May 15, 2026
Last chance
Sep 10, 2026
Your Lobelia Calendar
Set your location to turn these into exact dates and reminders.
Plant lobelia out in pots, baskets or beds
1 week after your last frost· every year
Cut lobelia back by a third if it stops flowering
60 days after your last frost· every year· optional
Water your new lobelia plants well while they settle in. Deep and slow is best.
About 1 days after you plant it
How is your lobelia settling in? Keep the soil damp, it does not like to dry out.
About 30 days after you plant it
Lovely work! If your lobelia looks tired in the heat, trim it back lightly and it will bloom again.
About 90 days after you plant it
The Journey Ahead
Lobelia's Lifecycle
Seedling
Mature Plant
Seed Production
Step 2
Planting & Sprouting
Growing Tips
- 1Give lobelia full sun where summers are mild, and afternoon shade where they are hot.
- 2Use potting mix with some compost in pots and baskets, or mix compost into the bed.
- 3Never let it dry out, because it wilts and browns quickly, so water baskets every day in hot weather.
- 4Feed pots with compost tea every 2 weeks to keep the flowers coming.
- 5Pair trailing blue lobelia with white alyssum for a classic basket.
- 6Lobelia is toxic if eaten, so keep it away from pets and small children.
Seedling Phase
Step 3
Growth & Maturity
20 cm
Mature Height
25 cm
Mature Width
Pests to Watch For
Diseases to Watch For
Mature Plant
Step 4
Harvesting
When to Pick
Blooms early summer to autumn; trim if it flags in midsummer heat
How to Harvest
- 1Lobelia is grown for its flowers, so care is all about keeping them coming.
- 2If it stops flowering or looks tired in midsummer, cut the whole plant back by about a third.
- 3Water and feed it right after the trim, and it blooms again as cooler weather returns.
- 4Pull the plants after the first fall frost and add them to the compost.
Step 5
Saving Seeds
Seed Production
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