Just a warning, this plant is not a true aquatic plant and only looks good in a tank while in its infancy. Cardinal Flower is traditionally a riparian plant, growing near the shores or streams and rivers. However, it is suited to grow in a woodland setting as well. At most, cardinal flower grows in a bog, but consistently water logged roots while eventually suffocate the plant.
I've purchased one of these plants couple years back,, I had it for about a year and it actually grew out of control. In an open aquarium it create stunning blood red flowers, but it is not a true aquatic plant, and unless optimal growing conditions can be provided it will fail to grow in an aquarium shortly. In my open aquarium i had about 3watts per gallon and 6700K bulbs...
I found one of these in a creek in Kentucky submerged. It was about 2 1/2 inches tall. I didn't know what it was until now. Now it is 12 inches tall. It grew this much in about a month. So far it looks great. No flowers yet though it is still under water.
I was sold this plant saying it was aquatic. So far, its easy to grow. Its grown alot over the past months. It grows at a moderate rate but the only problem Ive had is that green spot algae grow on the leaves. When you touch or hold the plant the roots are very hard and the leaves are rough and strong. Ive managed to make a medium height forest out of them, without any maintenance.
Very nice foreground plant. I have the small form of Lobelia cardinalis. Stays fairly compact in height, and tends to bush-out as it grows. Grown submersed, it loses the majority of it's purple color. Seems to do well with medium/high light, co2 supplementation, and water column fertilization. Not a very fast growing plant.
I have had it for more than 7 years, just trimming the top and replanting it. Discarding the bottom only when needed, otherwise the stem will have new brunches and leafs. Khuli loaches LOVE this plant, I have a school of 10 and they really really love them.