Do they need to be thinned? Are they in a pot or in the ground? Have you ever fertilized them?

Since they grow naturally in swampy areas, they like their feet wet. They also prefer an acid soil. If you have them outside the pond you could try some light feedings. They may need to be divided but rule of thumb is usually to divide when they start flowering less and since they've never flowered, I don't know what to tell you. If you do divide, only do it in the spring and early fall.

Jan

They are near the pond but their feet are not in the water so I will feed them with some acidic fertilizer and see what happens. This fall I may divide them and put some in the shallows. Thanks for your suggestions!

Two main reasons for flowers not to bloom are lack of sun and improper fertilization with too much nitrogen.