Winter spinach and a cold greenhouse

I sowed more seeds today (mache and red mustard) in our unheated teaching greenhouse (at the garden where I work).  It's an experiment in growing winter greens for the first time, following Elliot Coleman's inspiration in the Winter Harvest Handbook and Four-Seasons Harvest.

'bags' of spinach and greens:  note the water barrels providing transferred heat

It's quite remarkable. We've had unseasonably cool weather (it was down to 26°F last night) and the surface of the flats and bags was still slightly frozen at 11 am, but the ambient temperature was already 60°F.

Even though fall heat precluded sowing anything in the greenhouse until early November, lettuce, spinach, and arugula seedlings (sown in November) are thriving, and transplants of kale, mustard, and parsley are doing fine, too.

Of course, if I had sown these greens much earlier, they'd be larger and harvest-size, as they are in our outdoor kitchen gardens.  We've been harvesting mustard greens, cabbage, turnips, and broccoli for over a month now.

I'm wondering how my mountain beds of arugula, chard, and parsley are faring under much more severe conditions!