garten-pur

Zur Ehrenrettung der Tulipa tarda: Sie ist beinhart im Nehmen und unglaublich frosthart. Sie ist die einzige Tulpe, die in Klimazone 0b (= Null Be = Nordost-Kanada) draußen überwintert.

Hält sie auch feuchten Boden aus?

the ground is still hard frozen but the old snow stays only in the shaded places

To answer your question--sure, tulipa tarda is happy and reliable year after year in my garden. I am far too lazy to dig them up except to start a new patch somewhere else, and anyway, they wouldn't like it. I've tried several other species tulips but haven't had long term success with them. Mind you, this garden is on the wet side in summer, and so the conditions aren't the best for tulips. The tulipa tarda though, have been here for at least ten years. Greigii and kaufmania (might be wrong) are better suited to northern gardens than most. They' re okay for a few years, then become less.Other really hardy reliable bulbs are muscari and scilla. The old fashioned King Alfred type daffodils are pretty good too. The true crocus is really challenging in this garden, but possible, and I can't grow hyacinths. Your friend might also try winter aconite. I had some of that for quite a while, but I think it's gone now. Now I find out it needs moisture in summer--and of course, I had carefully put it in the best possible dry-summer spot.

Trees are a problem. The snowcover that works miracles with perennials doesn't help much, or at all, with trees. We're severely limited in our choices there. This link goes to the nursery that has been standard-reliable for people in this place ever since the town began. The nursery is south of us by quite a lot, but people here consider the trees and shrubs they offer as the ones most likely to succeed.

This other link may or may not be useful to you. It's a PDF file with the results of testing in various harsh weather sites in Canada. None of them are as cold or short season as my garden, but it's as close as we're likely to get. The info you'd be after starts somewhere around page 4.