The best place to ask this may be on the tomato forum. I find the larger the pot, the better the tomato does. :) I grew one in a 20g pot/tub and it thrived.

If you consider 5 gallons the dead minimum and that your yields will likely be reduced by the small soil volume, and 10-18 gallons as the norm, you're prolly pretty much on track.

Al

Al, I'm am new at this game this year and got a late start in S Florida for the best growing season. I've got about a dozen 5 gal buckets SWC ( really a misnomer since the older ones take 2 gal per day). The reservoir on the early single bucket ones is only about 1.5 gal and the "soil" is 3.5 gal. The oldest is a bigbeef and it has approximately 40 tomatoes some just starting to turn and a roma has over 60 on it but are younger. How many would you expect on the plant at one time in an 18 gal container and how many plants ??

bernie