Great blue lobelia

Questions about great blue lobelia

Does great blue lobelia need sun or shade?

Great blue lobelia grows in full sun (6 or more hours of direct sun a day), part sun (4 to 6 hours of sun, including some afternoon sun) and part shade (2 to 4 hours of sun, mostly in the morning).

It wants soil that stays evenly moist, rich in organic matter, and plenty of water. It copes with soil that stays wet.

What zones does great blue lobelia grow in?

USDA zones 4 to 9. It is hardy to zone 4, which means it survives winter nights down to about −20 °F (−29 °C).

Gardening in Canada? Use the USDA zone for your town: Canada's own zone map uses different numbers.

When does great blue lobelia flower in my zone?

In zone 5 it flowers early August to mid September. As a summer flower it moves about half a week for every zone: earlier where it is warmer.

Worked out from Hopkins' bioclimatic law: spring arrives about four days later for each degree of latitude north, and one zone is roughly two degrees. A warm spring or a cold one moves any garden two weeks either way.

How far apart should great blue lobelia be planted?

14 in (35 cm) apart, from the middle of one plant to the middle of the next. That is a little closer than its full width of 16 in (40 cm), so a group knits into one patch.

It grows 2½ ft (80 cm) tall. Give it the full distance from anything taller, or it will lean out towards the light.

How many great blue lobelia plants do I need?

At 14 in apart, set out in staggered rows:

• 9 to fill 10 square feet (about 1 m²)
• 9 for a single row 10 ft (3 m) long
• 28 to fill a 4 × 8 ft bed on its own

In a mixed border, plant it as one at a time, repeated along the bed at intervals; a slender one reads better as a clump of three.

In the bed above, the planner used three in three groups.

Is great blue lobelia poisonous to dogs and cats?

Yes: mild toxicity to people, dogs, cats and horses. Contains the same toxins as cardinal flower. Eating it can cause vomiting and weakness.

Rated from NC State Extension. Where references disagree, the more cautious rating is used.

Is there a pet-safe plant like great blue lobelia?

These come closest to doing what great blue lobelia does, and no toxicity is recorded for them:

• Peach-leaved bellflower: the same job in a bed, the same size and the same colour; flowers mid June to mid July, fine leaves, not medium.
• Rose turtlehead: the same size and the same flowering time; a drift, not an accent, pink, not blue.
• Purple moor grass 'Moorhexe': the same job in a bed and the same size; flowers mid July to early September, purple, not blue.

Matched the way the planner's Swap button matches plants: the same job in a bed, then size, then flowering time.

Do deer eat great blue lobelia?

Mostly not. NC State lists it as resistant to deer. No plant is proof against a hungry deer in a hard winter, but this one is low on the menu.

Will great blue lobelia spread?

It seeds itself about; the risk of it taking over is moderate. Self-seeds freely. Remove the spent flowers to limit seedlings.

What flowers after great blue lobelia?

Great blue lobelia is over by mid September. These start as it finishes and carry the same spot on, so it never goes flat:

• Garden chrysanthemum: from mid September to late October, 24 in tall, to stand in front of it and cover its fading stems.
• Toad lily: from mid September to mid October, 2½ ft tall.
• Blue wood aster: from mid September to mid October, 3 ft tall.

What does great blue lobelia look like in winter?

Great blue lobelia dies down to the ground and there is nothing to see until spring. The old stems can be cut in autumn, or left until spring as shelter for overwintering insects.

Is great blue lobelia good for bees and butterflies?

Great blue lobelia is visited by pollinators, butterflies, hummingbirds and beneficial insects.

It is native to the United States and Canada.