There are folks here with much more expertise than me, but I would think this depends on the type of bamboo and what "full size" is going to be. I've seen small pots with small species like "Golden Goddess" or "Lady Fingers" that were just about full size...but that wasn't saying much. On the other hand, a bamboo that is expected to be 3" thick and 40+ feet tall obviously will have to build up a good deal of root mass before it can produce and support something like that.

That being said, the more roots you put in the ground, the more you'll see growing above. The plants I've seen at the bamboo farm seem to make a bigger jump in size and maturity (and price) when going up from a 3-gallon to a 7-gallon. My strategy has been to look for deals on boos that I like and get the biggest I can afford...which usually isn't much. I think planting in fall might give smaller root balls a chance to bulk up during the cold seasons, which means you don't get to see shoots for several months, but hopefully better ones when you do.

It is the afford part that I am considering. I could get one variety in a 3 gallon container, or I could get 3 varieties in one gallon containers for the same price.

(It always comes down to time.) Do I let it get a slow start and continue building soil and preparing the site, or do I jump in and get it growing as quickly as possible?

Where is my time best spent?

I think that unless you're planting species that may be marginally cold-hardy for you, it's just personal preference. Do you want a bigger plant sooner, or do you want three different plants? I think the difference between a 1 gal. and 3 gal. might be one year's growth depending on the species.

If you we going with marginally cold-hardy species, then bigger would be better to help them survive the first winter.

Personally, I'd probably go for the 3 different plants than the one bigger one. =)

I have bamboo that are still sizing up from 5-gallon pots after 7 years, and I live in a Zone that is very conducive to hardy bamboo growth. If money is an issue, I'd opt for smaller, healthy plants and variety. There will come a point in a few years where it won't make a difference whether you started out with 1-gallon pots or 3-gallon pots. And, frankly, how you take care of them may make a bigger difference than that you started out with something somewhat bigger. I've got moso that I started from seed 6 years ago -- which means I was a year or two behind a 1-gallon -- and now it's about 20' high.

I bought 1 gallon plants in March and potted them into 5 gal. pots with potting soil and placed in full sun. I watered daily and fertilized them and by the end of June their root mass had filled the 5 gal. pots and the single culm plants I purchased had 4-6 culms after shooting season. I recently potted them into 10 gal. pots with the expectation that over the next 2-3 months they will fill these pots with rhizomes and possibly shoot again. Results are dependent on the quality of plants you purchase. A 12" twig recently potted will not preform the same as a 4' root bound plant with rhizomes growing out the drainage holes. Over the course of 3 months bamboo is capable of tremendous growth if provided with the proper amount of food, water and sun.