Those are what's referred to in the industry as nursery "trade sizes" and are not intended to duplicate a true liquid measurement but rather to standardize the sizing of plants in the commercial nursery industry. So comparing sized nursery containers to a 5 gallon bucket is really like comparing apples to oranges - one has absolutely no relationship or bearing on the other!! And FWIW, I would consider a 5G bucket an absolute minimum size for growing tomatoes. Might work OK for some smaller determinate varieties but I grow indeterminates in 20 or 25G containers and the root system will completely fill the container by the end of the season.

One gallon , by volume is a lot of roots. Separate the roots from soil mix (rinse it off ) Put its in a 5 gallon bucket and fill it with water. Now take the roots out and observe how much the volume/ level of water is reduced. That is the volume of roots, without anything attached to them. Another way to look at it: If the AVERAGE roots diameter is 1/16th of an inch , one gallon of roots will be about 6, 300 foot =2100 Yards. Lets take a more conservative estimate of average root diameter = 1/12". In this case one gallon of roots will be about 3500 feet long. If you think of average length of root to be 5 feet per root, then you should have about 700 individual roots. Somebody mentioned leaving finer roots behind. Even if so, finer roots don't have much volume. I am talking about TRUE volume not the visual appearance. Check this one! This is a typical double decker tomato root system. Mine were just like that when I pulled them out at the end of season. Even if you double or even triple it, it is not going to add to a root mass of one gallon.

I agree with Kathy! I say go for it! The only way to know what will work for you is to try it. Some people have terrible luck with tomatoes no matter where they plant them or what they do and some people just plop 'em somewhere and they produce a bumper crop with little care other than watering. The final outcome of one's harvest is highly dependent on many things we can't control ourselves. While I'm not using nursery buckets, I am growing 4 varieties of tomatoes in self-watering 5-gallon buckets ("global buckets") this year, two of which are determinate and two of which are indeterminates - early girl (which is an indeterminate that is nearly 7' tall with dozens of green tomatoes), better bush (determinate), roma (determinate) and San Marzano (indeterminate). I will admit the early girl is suffering quite badly from BER, but they have all been first fruits of the season and the plant has grown ridiculously fast. Once it slows down a bit on the growth, I expect BER will follow suit. If not, it's been a riot watching her grow. If she suffers from BER badly throughout the summer, I still might try again next year because her growth alone spurs comments of envy from the neighbors; which, honestly, is sometimes enough for me. :) The other 3 are absolutely thriving and have more tomatoes than I can even count. One tomato on the San Marzano plant had to be yanked because of BER, but the rest of those and all of the romas so far look amazing (many are egg size, but the plant is still pushing out a TON of blossoms). I also grow yellow squash, lemon cucumbers, Japanese eggplant and several varieties of peppers in 5-gallon containers with excellent results. I put two banana pepper plants in one bucket, but I do only one plant per bucket with everything else. Much of the success I've had so far this year is due the near-perfect weather we've had since mid-May. Some of the nights have been cooler than I'd like, but the days have been ideal in the 80s and 90s (with a few 70s thrown in here and there). I also make sure all of my containers have a constant supply of moisture by way of a timer and 1/4" drip line that fills the reservoirs of all 12 of my global buckets every 4 hours around the clock. A shower cap taped and clipped over the top of the soil keeps everything perfectly moist without being saturated, as the plants only get their moisture from a "wick" that hangs into the reservoir below. I won't go into extreme detail since an internet search for "global buckets" will show you what I'm talking about. It worked extremely well for me last year (with less than ideal weather conditions) and is working even better for me this year. At the end of the day, you could set your garden up exactly like mine or the next guy over and we could all have completely different results. If you want to try it, give it a go and see what happens for you! Take good notes and learn from your observations. It's amazing how much we think we'll remember, but.. :) This post was edited by NBM81 on Thu, Jul 10, 14 at 12:02

Since you're Zone 11 the trick to a smaller container is that with smaller soil volumes and container diameter you have to keep the soil from getting too hot, so I'd try to shelter the base/container from getting too much direct sun.