Little elm

I have a small Ulmus I bought last summer. Most likely a chinese elm, which I bought at a big gardencentre. I might have asked earlier how I should keep it during the seasons, and If I remember correctly I was told to have it outside during the winter. It gets really cold, so only 2 of my trees are outside atm. Right now its only -3 c, but it was almost as low as -20 a week ago. Now I was reading something on a bonsai site:
"Very vigorous and hardy outdoors in most areas. We recommend keeping Chinese Elm Bonsai outside where temperatures do not drop lower than -8 Celsius. If kept outside the tree will lose most of it's leaves in winter thus displaying it's lovely fine ramification. Prefer to be cool over the winter if kept indoors."

Does that mean I have most likely killed my little tree?

-Storm

Storm wrote: Right now its only -3 c, but it was almost as low as -20 a week ago. Now I was reading something on a bonsai site:
"Very vigorous and hardy outdoors in most areas. We recommend keeping Chinese Elm Bonsai outside where temperatures do not drop lower than -8 Celsius."

Does that mean I have most likely killed my little tree?

-Storm

-20 degree Celsius = -4 degree Fahrenheit
Possibly. Depends on how big the tree is, where the roots were, how long it was outdoors, & how long the cold dip lasted. If you keep your bonsai outdoors, the pots should be buried & the tops covered with a thick layer of leaves, Styrofoam, or some other insulation. Here in Zone 5 (where I think you are) I have successfully wintered trees rated for Zone 6 with the above precautions. I use what we call rose cones, thick cones of Styrofoam designed for this purpose.
Iris