Blue Cardinal Flower

Lobelia siphilitica

Blue Cardinal Flower partners perfectly with its red-flowered sibling, blooming at exactly the same time with the same upright habit and the same preference for moist soil. The rich blue-violet flower spikes are intensely saturated and hummingbirds visit them alongside the scarlet cardinal flower in a late-summer combination that's hard to beat. Plant both together along a stream edge or rain garden margin for a mid-border display that runs for weeks. It's longer-lived than Lobelia cardinalis in garden conditions and tends to form more substantial clumps over time. The white-striped blue flowers are more accessible to bumblebees than the hummingbird-tuned cardinal flower, so the blue species serves a broader pollinator audience. Self-seeds modestly in moist conditions. A garden classic for good reason.