New greenhouse and 4 Winds rootstocks?
I'm building a16x32 greenhouse that'll be closed in by next winter. I'm planning on planting several citrus trees in the ground. Since the greenhouse will be heated with a subterranean system the temperatures might drop below freezing on occasion. I've always figured it'd be best to plant on flying dragon. I've always assumed (wrongly it turns out) that 4 Winds propagates on FD. They use Troyer (a trifoliate) for mandarins and a few other things but Cuban shaddock for most.
Everyone loves the stock they receive from 4W but I can find out nothing about the characteristics of the shaddock. It's an obscure rootstock used by no one else apparently. I guess I'm concerned that it's not going to be appropriate for a northern, barely heated greenhouse---less cold tolerance than flying dragon-the trees won't become "dormant" in the winter, etc.
It seems that there aren't mail order nurseries around any more that ship to the north and propagate on FD--at least none with any selection (4W offers every tree I'm looking for).
Does anyone have any thoughts on the Cuban shaddock and its hardiness or general suitability for a northern cold greenhouse? Of course thanks in advance for any help.