Hi Tropicaltoba!
I am not nearly as cold as you, but in Idaho I do have to have a greenhouse and all my tropicals are in pots.
I have not had great luck with organic fertilizers in pots, because there isn't any "soil" in them so to speak, and organics have to be broken down by soil microbes before being available for the plants to use. It takes a long time, so you have to be patient to see results, and adding beneficial fungi and microbes is really important.
I am lazy and impatient by nature, and just use MiracleGro mostly, although "The Bobs", aka my worm composting setup, contributes a lot.
Can we see pics of your greenhouse???
Carolyn