I have 3 grow bags x 20 gallons. I want to use them for growing zuchini 1 plant/bag. I have cavili and golden rush. The plan is to start them in cups on the porch and transplant into bags around 4th of july. To avoid squash vine borers and delay powedery mildew.

Is 20 g size enough for them? What would be the best growing media commercially available?

Thx