Using grow bags for guerilla grow?

I ordered a pack of 2 gallon and 3 gallon grow bags for my outdoor grow since i hate carrying pots to my grow area. I plant on having my plants grow to about 3 ft and i read somewhere that for every gallon is about a foot of plant. Here is a picture of the grow bags i got.

http://www.amazon.com/Gal-Grow-Bag-10-ea/dp/B002JLJEQO/ref=sr_1_2?ie=UTF8&s=home-garden&qid=1276871211&sr=8-2

I can always get 5-7 gallon bags but in the area i dont see the need for having a plant 6 feet tall since near the end of the season it may draw attention if someone happens to walk by. What are your opinions on using grow bags and you think these size bags are ok for a smaller type of grow? How big do you think the plants will grow in each size bag when full flowering? If you need any info to help with your answer ask please. thank you.

Bags are fine to grow in, they just fall over sometimes, much more than pots, so I suggest you set it into the ground a bit. I'd also flip those inside-out, cause it looks like they're black on the inside. The white on the outside would be good 'cause it would absorb less sunlight, making the soil retain moisture a little better, but you're trying to keep secrets, white things don't keep secrets.
As for the height of your plants and the amount of gallons you'd need, that has a lot of variables. Have you started your seeds yet? Does your spot get full sun? What are your average temperatures during the day? Is your climate arid or more towards temperate rain?
Really, the 1ft = 1 gal is an indoor rule of thumb since you can control your climate so easily.

My plants are started about 4 days old but healthy none the less. spot gets full direct sun alllll day. avg. temps are between 75-90 the temps are perfect that i do no of and when it rains its nearer 70 but goes back in the 80s after a day or so. very ideal and my climate is temperate i think. i live in new jersey so yea temperate should be right.

And since the 1 gal 1 ft what would it be outdoor? bigger since its natural sunlight which is the best light for it? Or is there really no way to even remotely determine the height from the container size?

Okay, you're in the same climate as me. Since they're already started I would highly recommend 5 gal bags, or cutting some holes in the 3 gallon so the plant can continue to root out. Especially come late July and August, when the temps average out at around 90 and get up to close to 100s, you're gonna be watering them at least once a day if they remain in 2 or 3 gal bags.
I have no rule of thumb for container size for outdoors, I dig holes or make raised beds. And let me tell ya, in a 3ftWx3ftLx2ftDeep raised bed, if it doesn't rain in a week, I have to water it pretty good. Go with the 5gal if its not too much trouble, if so, cut the 3gals

5 gallon is usually good for anything grown from seed. I've had plants up to about 12-14' in those. If you veg'd indoors before planting outside you might want to move up to at least a 7gallon. You will rarely outgrow that.

Photo: an example of a rootbound plant in a greenhouse. Some slight yellowing has started at the lowest internode...an indication that nitrogen supply is running low and that it’s time to move the plant to a bigger container. During vegetative and early flowering time rootbound plants quickly yellow because nutrients are depleted in the container. Fertilizing is rarely a satisfying long-term solution and rootbound plants should be repotted as soon as possible. Mandala strains have very vigorous root development and require a sufficient container size to support their quick growth.

Ill buy 7 gallon bags also. If i need to ill just transplant the 2/3 gallon bagged plants into the 7 gallon ones. dont see the harm in that. I get 10 bags per order so i may keep a bagseed plant in the 2 or 3 gallon just to see how it turns out but my other plants will get transplanted no doubt. thanks for the help guys.

You would be much better off just buying some 15 gallon or bigger grow bags. I can understand not wanting to haul soil to your grow area, but if your able to, you're going to have way bigger plants. 2 or 3 gallon your plants will become root bound easily. 7 gallon will work fine, but your plants will spread out much more with a 15 gallon. Personally i went with smart pots as I've heard they work the best, cost about 8-10 dollars for a 15 gallon one. check my video http://www.youtube.com/watch?v=2BTWJQgOZY4

my 15 gallon grow bags cost 1.50 a piece cant beat that sure smart pots are better but if you dont have alot of cash just get the plastic grow bags work fine.

If i use 15 gallon wouldn't the plant be like 8' tall or even higher?

depends when you planted them, you can top and LST your plant so it stays short, thats what i'm gonna do, just topped this Church on it's 5th node

If i top how much shorter would the plant be? if it would have gotten to about 4 ft without any type of training.

Hard to say, just top as desired. Once it gets too big for your liking, top it.

if you top it when its young like mine it will grow a lot less shorter as it puts energy into 2 heads instead of 1, mind shouldn't get much taller than 3 1/2 feet or so