Water hyacinth, parrot's feather questions

Does anyone know when it is okay to put these out? I put them out too early last year and they did not do well at all. What temperatures should it be when I put them in the pond? Thanks.
ShirleyC

I live in the Shenandoah Valley and the garden shops around here don't even sell them until May because it's too cold earlier. I would guess Laurel would be about the same. Our last frosts can be as late as mid-May.

See the plantfiles:

http://davesgarden.com/pf/go/661/index.html
http://davesgarden.com/pf/go/1258/index.html

The water hyacinth is tropical, and I would assume that temperatures would need to be above 50 F for good growth. The plantfiles said that the parrots feather has grown even in freezing conditions.

Thanks for the input. The nursery I purchased it from told me today they had put their water hyacinths outside in their ponds so I suppose I will try mine. I am delighted to hear the parrot's feather can go out as well.
Shirley C

Wyld. Here in Michigan we use the rule " After the last Frost", which around here is about the middle of May, and the water is at least 65", they don't like cold water.
I had parrot feather that took over the pond, now we keep it cut way back, And winters here get down to -10". It is a survivor