A few more comments here.
Per-åke: yes I forget ground elder, we've managed to keep it out of
this garden so far I suppose thats why! We used to eat it in our old garden
it tastes almost better than spinach.
Ronald: Indeed our biggest environmental problem (in southern Sweden, and in my opinion)is natural vegetation!
I know most of the rest of the world has the opposite problem, but here everything grows like crazy
and just swamps our historical farmlands. We don't have enough cows to keep it back, sheep are too effective
so we're losing wildflowers at a depressing rate. To a lesser scale (and our own fault)
we have the same problem in our garden, most of the nice bulb plants we plant grow well but then disappear amongst the weeds, we just can't keep up with the weeding, and then the winter kills them anyway!
Adam: ducks yes, do all kinds of ducks eat snails? Don't ducks create problems of their own?
We do have a big pond so we have thought about it, are ducks a lot of work and can you
leave them? What about the winter?
Boyce: Purple loosestrife (Lythrum salicaria) is a fairly common plant here, but well liked
and not at all a nuissance. Even more ironic is Water chestnut (Trapa natens) which is a nuissance
in the Hudson river, yet an almost mythical and sadly extinct plant here. It is said to be the
only plant made extinct by botanists, last one was seen here in 1913, it is suspected that
the hobby of herbarium collections in the 18th century finshed them off!
Finally I'd like to warn about a pond plant called Bog arum (Calla palustris) which looks
like a bulb plant but in fact isn't. We once found some growing wild (it's not uncommon here),
and threw a little bit of it in our pond, a couple of years later (to my delight at the time)
it turned up as a nice plant. Now after five years I hauled out 10 wheelbarrow loads of it.
I doubt if I can exterminate it, but I'm certainly going to try.
/Neil
(western Sweden where we're having a very wet summer)