Kratom fertilizer

I'm just curious if anyone has discovered a specific fertilizer or ratio that send to be the best with kratom specifically. Also, if be really interested to hear ideas about how to keep my trees warm in the greenhouse this winter. Anybody have any good ideas? I wish I could find a good solar heater that was halfway affordable but I haven't seen one. May just have to use a little wood stove piped it the top of the greenhouse or else two or three heat lamps hanging down. It's 20 x 10, the girls are in the ground, all one half of it mostly.

Have you tried fish emulsion? 

I use alaskan fish emulsion fertilizer. Comes in gallon jugs for $20. Best thee is!