if you dont have big pots(15 gallons or more) then definitely dig big holes and bag them-You can contain the roots and still give them enough space to spread if you dig a big enough hole.You dont want your roots extending out of your soil mix into bad soil-particularly clay which is very common.Dig a 3' by 3' hole, pour 2 to 3" of gravel or rock at the bottom for drainage, and place a large trash back with holes cut in the bottom for drainage.Try Heavy Harvest from Advanced-time release pellets that you apply once every season.(Spring,Summer,Fall.)