Although annual types are widely available at garden centers in the spring, you can also start your own plants from seed, sown indoors 8 to 10 weeks before the last spring frost date. Don't transplant seedlings outdoors until a few weeks after the last frost date.

When can lobelia be planted outside?

Sow seed in late winter or early spring, under glass, at 16-18°C. Prick out into pots and plant out in late May, once all danger of frosts has passed.

How cold can lobelia tolerate?

The Lobelia x speciosa varieties are perennials. These are hardy to 5 to 14 degrees Fahrenheit (-15 to -10 C.). Either variety needs well-draining soil in full sun for best blooming. The annual forms tend to get weedy when temperatures get hot in summer but can be rejuvenated by cutting the plants back by half.