Are the roots submerged less than 1 inch deep? What are the nutrient levels in the pond, especially nitrogen? Do you have fish in there?

Yes, only the roots are below the water, no, no fish. Dont know about the nutrient levels, but the ponds about 4 years old and all the other plants are thriving

Hmmm...a little hard to tell what's going on then. The water level is good. Since your other plants aren't suffering, it's not likely to be nutrient problems. I know that they aren't real fond of water with high calcium or sodium levels, so if you get a lot of crust at the water level, that might be a problem. I don't know what your weather has been like, but if the water is cold, that will slow them down considerably--they may just now be gearing up for the summer.

ok thanks. I thought they might just be taking a while to establish. I live in Newcastle up north, but its been pretty warm

Sorry that I couldn't help more, Howee! I usually have had problems with too much heat, but my ponds tended to heat up almost to bath temperature, if I didn't do something about it!