Lobelia in winter will die back no matter which variety you have. However, the annual Lobelia may not come back at all even if it formed seed. ... The annual forms tend to get weedy when temperatures get hot in summer but can be rejuvenated by cutting the plants back by half.

How do I get my lobelia to bloom again?

This includes trimming to remove spent blossoms. For spiky types, wait until the entire spike has faded before clipping out the stems. Cut back the plant by half or more at the end of its bloom period. Trimming back lobelia plants keeps them from looking messy, and it may encourage another flush of blooms.

How do you winterize lobelia?

Spread a 2- to 3-inch-thick layer of mulch over the root zone. Too much moisture can kill lobelia during the winter months, so only water it when the soil feels dry beneath the surface. Stop fertilizing lobelia plants in late summer to give any new growth a chance to harden off before the first frost.