Late-summer blues: Great blue lobelia and willow gentian

Judith Adam

Updated on:

Blue lobelia (Photo by Brendan Zwelling)

I haven’t been paying much attention to my shady air-conditioner garden, and was pleasantly surprised to pass by and notice two gorgeous blue perennials in bloom — great blue lobelia (Lobelia siphilitica, 24 x 12 inches /60 x 30 cm, Zone 5) and willow gentian (Gentiana asclepiadea, 18 x 15 inches / 45 x 38 cm, Zone 6). They look particularly vigorous this year, no doubt because of the copious amounts of rain we’ve had. These plants like moisture, and will put on a show in either full sun or part shade. But both of mine are looking good in this bright shade location with no direct sunlight.

The great blue lobelia started as one small plant and has been politely increasing its girth. I know it can self-sow, but so far I haven’t noticed any volunteers, although I’d be glad to have them. Seeing how well lobelia responds to adequate moisture, I should provide more frequent irrigation, and then I might have seedlings. Rising from a compact leaf rosette, the stiff flower spikes are covered with individual florets, opening from the bottom and moving up the flower spike over four to six weeks in late summer through early fall. (Lobelia is toxic, but safe to handle and grow if you know not to ingest it.)

Cardinal flower (Lobelia cardinalis, 36 x 18 inches / 90 x 45 cm, Zone 5) is a fiery red cousin to great blue lobelia, but definitely does better in a sunny location. Its named selection, ‘Fried Green Tomatoes’ (L. c. ‘Fried Green Tomatoes’, 30 x 18 inches / 75 x 45 cm, Zone 5), is an incendiary red, and reputedly a long-lasting perennial. Lobelias are often described as short-lived plants, and I suspect that has more to do with inadequate growing conditions, rather than any instability or lack of plant vigour. This summer’s abundance of rain has shown me that they thrive when given enough moisture, and perhaps a thick mulch of leaves in winter.

The graceful willow gentian is fortunately a little distance from the lobelia, so that it shines on its own and doesn’t have to compete with another shade of blue. (The distance between these plants doesn’t reflect any amount of thoughtful planning on my part — it just happened that way.) Willow gentian is another long-blooming, late-summer plant, and it’s still carrying lovely blue flowers along its horizontal stems. The plant has been in place for about a decade and produces six or seven long stems each year, with no increase beyond that. Possibly if I gave it more moisture and a bit of encouraging compost, it might increase its size in the shady bed. Or, a move to a sunny location might bring on a growth spurt. But I’m inclined to leave both the lobelia and the gentian in the shade. They both make the air-conditioner bed a special and interesting place, and that helps to distract me from noticing the mechanical monster they share quarters with.


Print Friendly, PDF & Email

Leave a Comment