20130317b-17ok.. maybe not plants but at least seeds.
The peppers went in on Saturday March 16th, 2013.
Low that night was -13C but the partially insulated greenhouse with small electric heat stayed warm enough.

Onions were planted on Saturday March 2nd, 2013. Tomatos will probably be into April as, unlike last years March heat wave, it is still quite cold out.
The little electric heater is about 1kw and is probably on at least 16hrs/day right now.