Can you help with passive solar greenhouse exterior wall details?

To build a passively heated greenhouse in a cold climate that can operate for 3 seasons you would need to find a way to store the heat. Insulation, vapour barriers and air barriers are important, but in order to retain heat from the day you would need to include some sort of thermal mass.  I would say your first step is to check out our page on building greenhouses –

How to build a greenhouse in a cold climate

Finding a way to store the heat will not only allow it to stay warm longer, that can also be a way to prevent it from overheating as well. Since a greenhouse will obviously have a lot of windows or clear plastic where there is little to no R value, insulating some portions of wall will help, but only so much. 

Since you say you started already it's a bit late for us to help too much unfortunately, but...we recently installed a slab on grade with a solar air heated floor,  it’s not fully ‘passive’ as it requires a solar air heating panel, but that only requires a fan which can be run that off a very small PV panel.

As for:

Vapour barrier: Check with your municipal building inspector, for a higher humidity environement they may have requirements beyond the standard 6-mil poly barrier. 

Best insulation - maybe Rockwool, it is unharmed by moisture. Same for the rigid insulation, EPS and XPS will stop moisture, Rockwool will let it pass right through, read more here -

Choosing the right rigid insulation panels 

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