Lobelia Cardinalis winter care

Unionworkeruk

I have three plants 5 foot tall grown in the pond Now its winter  do I cut them back to near the surface of the pot and do I leave in the pond which no doubt will freeze at some time

I have conflicting advice  Cut back and put under cover  Cut back and sink them in pond and just leave them alone, allow foliage to die and cut back in spring

Any advice ?  Thanks

Perki

I've but mine back  which are in the ground. I thought Lobelia C were marginals the whole plant  shouldn't be under the water just part of the root system. 

Obelixx

Lobelia cardinalis is a marginal plant that can be grown in moist beds or shallow pond margins.  It doesn't need to be submerged.   I would leave the stems on till spring partly to mark where it is and partly to take the worst of the frosts and protect the crowns till new growth starts in spring.

It is only hardy down to -5C so needs protection in gardens exposed to more extreme cold weather.    

Unionworkeruk

Only part of the root system, most of the pot actually, is under water and plants have been great  I take it if the pond freezes as it will do for a few days only,  I suspect, in London they will be OK if I just leave them to it and cut back the old foliage in Spring  Thanks