I only occasionally grow in pots but I would think the plants need the same nutrients in pots that they do in ground. I use whatever organic tomato/vegie fertilizers that are the cheapest at the time, Dr. Earth, Jobe's, Kellogg's. They are all good. I think the important consideration is that it should be 'certified organic'. It should say so on the bag. A good and independent private or public agency should certify that it is truly organic, don't just trust the claims the company makes. I think OMRI is still the gold standard for organic certification but many states (Washington, Maine, California etc.) now have their own agencies which do the same thing. Just don't overdo it. Just one plant can give you and awful lot of zucchini!
