This is a really nice plant. Blue cardinal flower, Lobelia siphilitica, is an easily grown, herbaceous perennial, native to eastern North America and hardy to USDA zone 4. It needs fairly moist soil and does better here in part shade, where the ground doesn’t dry out so much, or in full sun in pots where it gets regular watering. It blooms over a fairly long period, which is always appreciated. One thing I didn’t know about it is that the species name of siphilitica is from “a prior medicinal use of the plant in the treatment of venereal disease.”
It does well in our garden and we have it scattered around. This particular plant is growing in a container on the driveway with black-eyed Susans behind it. Blue and yellow is always a good combination in the garden and with yellow being so prominent in ours, adding that touch of blue is great.