Great Blue Lobelia (Lobelia siphilitica) is covered in deep blue flowers in late summer and early fall. It can form colonies of flowered spikes in medium to wet soils, especially with a little shade. Longer lived than the Cardinal Flower, it also attracts hummingbirds. Planted together, the two Lobelias make a stunning combination. Excellent for damp clay soil. Hardy to Zones 3 - 9.