I wondered this when OP asked about 50gal.
I would do a planter if I needed to keep them mobile, but my limit for that is ~12-15 gal containers.
I thought about this, too. My natural dirt is… well, it’s plain awful. But digging out it a reasonable hole to add dirt to doesn’t sound so horrible either. … maybe at 100 gal capacity and as many plants as you run, I’d be singing a different tune. 
That’s my thinking, I mean that’s how we build up gardens pretty much
The native soil where I live is clay and caliche. Its horrible soil so I make my own. I dig big holes and fill with my own soil. If I used grow bags they’d be 50gal minimum. A 50gal bag is unmovable so why not just grow it in the ground.
@plumbdand is dead correct on this one. Even if your native soil is not the best you can still dig a giant hole and creat your own mix for it. Not only will the plants roots tap into the ‘undesirable’ soil they won’t ever get root bound.
Plus the ground temp always stay a little warmer. The roots will never be hit by a direct wind chill.
If you can go this rout I would do it. I would if I could but our ground is straight lava rock. Had to call a well driller just to set a few corners for a shop a few years back. It was hell. Lol.
Thats something else ive been thinking about. Why grow in a bag when you can dig a hole? Is there a difference?
I think the main advantage for me is the watering part of the whole thing. I think i would benefit fro. Watering by using the bags because my ground is hard ass clay and doesn’t really absorb very well
10 gallon, Anything bigger is to big to tote. I use to use them and cut the bottom as they dry out too fast unless the roots can get to the ground.
I have found that starting the plants in 3 gallon pots then cutting the bottom off the pot and planting it in a pre dug hole leaving the top three inches of the pot above ground works way better than bags above ground. The pot acts as a channel to direct the water to the roots. Beats the heck out of toting water 
Thats a damn good idea! I just might do that…
Just be sure they are not your wife’s pots. You can tote a 3 gallon pot with a nice sized pre started plant a long ways to be transplanted as well. Bags must be watered twice a day above ground in summer. Pre dig a two foot wide by two foot deep hole. I initially put a little lime but check your ph first, and then a handful of triple 8. I then just add occasional feedings in my water. Sprinkle cayann pepper in soil and around pot to deter ants and termites. Drop a couple moth balls in bushes around plants but not to close. Top dress with manure or organic fertilizer once flowering starts. Add gypsum and oyster shells to soil to increase calcium. Good Luck.
Cool, thanks!
I live in an area where absolutely nothing growes without the soil being ammended. Its hard as hell to dig you have to use a digging bar or a jack hammer with a spade bit to break it up. Worse when its wet it has the same color and consistency as potery clay and sticks to everything. You have to use 2 shovels, one to scrape the mud/clay off the other one. Most of my garden is 3ft thick of soil Ive been making for the last 16yrs. I have a duck pond next to both of my greenhouses, once my plants roots are established they are drinking from the pond.
Sounds like you got it pretty tough. Cool your plants roots drinking from the pond. Man my soil is almost as bad as yours. Its not really possible to plant plants directly into it…
Every couple of years I dig the pond back out and put the spoils into my garden and mix it with compost and a shitload of other stuff. The pond doesn’t need a liner the clay holds water really well. My yard is sloped and the greenhouses sit at or below the water level of the pond around 3-4ft away.
You couldn’t ask for a better setup. Nothing like Gods fresh rain water
We are on a well I have to run water for an hour every few days to keep the water level where I like it but when it rains a lot of my yard drains into it.
I have 3 photoperiods (12wks, 24”) in 5g plastic pots, they aren’t holding enough water. I’m thinking about transferring to 10g fabric pots, but want to avoid damage or shock to plants.
Considering cutting slits down sides of plastic pots, then putting them in larger pots, WITHOUT REMOVING the plastic (roots will spread through slits, whole plant will have more soil and hold more water).
Concerned that removing plants from pots and re-planting root ball directly in new soil will cause shock and damage.
Thoughts?
Oh, sorry. Outdoor grow, above ground, hand watering, West Coast, 2x/weekly feeding w/Jacks.
I started with 10g fabs. And realized thats not enough either. So 30 to 45 gallons i would recommend.
My first time in big pots too. I grew in 20g fabs last year. They did fine. But i wanted more water holding so 30s and 45s this year. I just give my pots a good squezee, and tip them upside down while holding the stock between my fingers and they pop right on out. May have to do a little coaxing. 
No concern about exposing the roots? Or slowing growth down by giving the roots more room to spread?
I was thinking if I slit the sides of the existing pots, the roots will expand through the slots into the soil over time, but it won’t be a free for all
No. Thats not good. Its ok, there tough. Its gonna be exposed for seconds no big thing. If you do it your way its gonna be worse. Just a bad idea. Dont be afraid to transplant.
