Gadenin日本語Get the appThe shape of the lobelia year
Lobelia takes about four months from sowing to a plant worth putting outside, which is considerably longer than most bedding, and that single fact sets the calendar. Sowing goes in during late winter, ten to twelve weeks before the last frost, and the plants are not planted out until soil and nights have genuinely warmed a week or two after that frost date. Everything else follows from those two anchor points.
The growing season itself divides into three parts. There is a first flush from early summer, running for perhaps six to eight weeks, which is when lobelia looks its best. There is a mid-season check, when heat and dryness brown the plant out and it stops flowering. And there is a second flush after you shear it back, which carries through to the first frost. Planning for all three, rather than treating the mid-season check as a disaster, is what makes the plant reliable.
In a cool summer with nights dropping into the fifties Fahrenheit (10 to 14C), the middle check may barely happen and the plant simply flowers continuously. Where nights stay above 68F (20C) for weeks, the check is longer and the shear back should be timed to land as the heat breaks rather than during it. Everything below assumes a temperate summer and shifts accordingly.
| Stage | Timing | Main job | Watch for |
|---|---|---|---|
| Sowing | 10 to 12 weeks before last frost | Surface sow on damp compost, uncovered | Slow germination, 14 to 21 days |
| Seedling growth | Weeks 3 to 7 after sowing | Bright and cool, water from below | Damping off, leggy growth |
| Transplanting seedlings | About 6 weeks after sowing | Lift clumps of five to eight into cells | Do not separate seedlings |
| First pinch | 3 to 4 weeks before planting | Shear the clump level, take half an inch (12 mm) | Pinching too late delays flowering |
| Hardening off | 2 weeks before planting | Increasing time outdoors | Cells drying out in wind |
| Planting out | 1 to 2 weeks after last frost | Plant close, water in, keep damp | Cold soil below 55F (13C) |
| First flush | Early to mid summer | Water daily in containers, feed lightly | Compost drying at the center |
| Mid-season shear | When browning and flowering stops | Cut half off, soak, feed at half strength | Shearing a dry plant |
| Second flush | Late summer to first frost | Keep watering, light feed | Mildew in cool damp nights |
| End of season | At the first hard frost | Clear and compost the plants | Do not try to overwinter bedding types |
Late winter and early spring: sowing and the slow phase
Sow indoors on the surface of pre-watered seed-starting mix, uncovered, at 65 to 70F (18 to 21C), and expect two to three weeks before a green haze appears. Take any cover off the moment it does. From then until about six weeks after sowing the seedlings sit at half an inch (12 mm) tall and appear to do nothing, which is normal and is the plant building roots. Keep them bright, cool at around 60F (15C), and evenly damp, watering from below.
Transplant at about six weeks, lifting clumps of five to eight seedlings on a plant label and dropping each clump whole into a cell. Do not separate them. Grow on cooler still, at 55 to 60F (13 to 16C), and start a quarter strength liquid feed once they are visibly growing away.
Give the first pinch three to four weeks before you intend to plant, shearing the little clumps level and taking half an inch (12 mm) off the top. That timing means the side shoots have broken and extended before the plant goes out, so it arrives in the basket as a dense cushion rather than a chopped stump.
Late spring and summer: planting, flowering and the shear
Harden off over two weeks, then plant a week or two after the last frost once the soil has reached about 55 to 60F (13 to 16C). Space clumps four to six inches (10 to 15 cm) apart in the ground and three to four inches (8 to 10 cm) apart around the rim of a basket, and keep everything consistently damp for the first fortnight without exception.
The first flush follows within three to four weeks of planting and runs through early summer. The job through this period is water, and in containers that means daily and sometimes twice daily in heat. If you mixed slow release fertilizer into the compost, no feeding is needed for about three months; otherwise a balanced liquid feed at half strength every two weeks.
When the plant browns in the center and stops flowering, shear it by half, soak the root ball right through and feed at half strength. Regrowth breaks in five days and the second flush arrives within ten days to a fortnight. Time this cut for the point where the worst of the heat is passing, and do not do it later than about six weeks before your first expected frost, or there is not enough season left to rebuild.
The two dates worth recording every year are the day the first flower opened and the day you sheared the plant back. Those two, set against your sowing date, tell you next year whether to sow earlier and whether your shear was too late, and they are far more useful than any general calendar.
Autumn: ending the season and planning the next
Bedding lobelia is treated as an annual and finishes at the first hard frost. There is no benefit in trying to overwinter the plants indoors; they go thin and woody, carry pests through the winter and never regain the density of a fresh spring-sown clump. Clear them out, empty the containers and compost the plants once they have blackened.
Some plants will have shed seed into the compost, and self-sown seedlings sometimes appear the following spring in beds and gravel. They are worth leaving where they turn up, but do not rely on them, because bedding lobelia is usually a hybrid and the seedlings vary widely in color and habit.
This is the point to review the season's notes and act on them. Which baskets needed water twice a day, which positions browned out first, whether the shear back came early enough. Lobelia responds so directly to water and heat that a couple of seasons of specific observations from your own garden will improve results more than any change of variety or feeding regime.