They will have a really hard time in those pots in another month or so probably. Not having more space for the roots means that the plant will stop getting bigger. And if the plant gets outbound it can be super bad for it.
Miracle grow is a no no for weed growers. The slow release fertilizer is not ideal as your weed plants have different nutrient needs during each stage of the grow cycle.
My advice to you would be to buy 7gal grow bags and use an organic soil like happy frog or one that home depot carries. Soil and perlite. When you transplant, loosen up the root ball by rolling it in your hands a little. (Freshly washed hands!) Let as much of the excess miracle grow soil fall from the roots as you can without losing your hold on the root ball. It might be helpful to have a second person helping you to hold the plant by its stalk. And then gently set the plant into the new grow bag. Backfill with the new soil mix. (Premoisten the soil in the grow bag b4 putting the plant in. Not super wet but you want a lil mostuire in there for the roots to go find.)
The benefit of using cloth grow bags is that the plants don't get rootbound. The roots are able to poke through the bag and then the tips dry up and die, "air pruning".
I hope this answered some of your questions!
