I agree. I have great luck with organics like the fish emulsion. And foliar feed, as Tog has mentioned. I do it with tomato transplants every time, exactly as he has described, with excellent results. No shock. It stinks, (whew!!!) but works
Also, the Superthrive. It allows the plant to not have to seek out it's own hormones needs from roots in new soil, it directly allows the plant to uptake them. You can even apply it to the undersides of the leaves, or roots if plant was exposed at that time. Anyway, I lose a good 70% less plants when using the Superthrive. It's really worth a shot. I can't find it at Home depot, but Lowes always seems to carry it, especially at this time of year.
And to Alpha, Yes, that's a challenge, a pot that large. Great to have a backhoe when talking 300 gallons
Gino