My go-to reference (Ohio State University FactSheet - Container Vegetable Gardening) cares more about depth of pot than gallons.

"Dwarf--12" deep, Standard--24" deep"

That might be a factor.

[perhaps also with the higher moisture exchange they are giving a margin of error, in case the gardener cannot be on hand to monitor moisture levels.]

I know that commercial greenhouse growers go much denser, with "5 gallon poly bags (video).

I don't have a greenhouse ... but I do have drip irrigation, and can do a couple cycles of slow drip every day ... so I'm thinking of the 5 gallon poly bags for next year.

This post was edited by johns.coastal.patio on Mon, May 5, 14 at 19:23

I posted the following in response to another forum question, but it would be applicable here as well:

As for pot size, consider whether you plan to extend a plants growth over multiple seasons. Some people prefer larger pots (greater than 10 gallon), but they typically live in warmer zones with longer growing seasons. Since they have the time to grow larger plants, larger pots can be helpful. I live in MN so this would not be an absolute requirement. I'd go for a 5 to 10 gallon pot. There is no sense on spending a fortune filling 20 gallon pots with mix for one growing season.

Also consider that the recommendations provided by the manufacturer of the pots mean more revenue to them (larger pots are more expensive). I successfully grow peppers in 3 gallon pots. I've read about master gardeners that produce high yields in 2 gallon pots. Tomatoes will require larger pots, but 20 gallon is not necessary.

You must consider all factors. The type of plant (determinate/indeterminate), the growing medium, the zone/climate, etc. Also consider sun/shade availability. If you need to move the pot around, can you really move a filled 20 gallon by yourself? All these things should impact your pot sizing.

Those pot sizes are pretty close to ideal regardless of whether fabric pots or plastic. Determinate tomatoes need at least a 10-15G container, indeterminates even larger. Peppers being smaller sized plants overall can handle a smaller sized container. Melons and squashes are big plants and will require a larger container.

Here's something to keep in mind - plants that tend to grow large also tend to have commensurately sized root systems. Indeterminate tomatoes can easily reach 6-8' and melons and squashes are also large, spreading plants that will produce large root systems. Confining these to too small a container stunts growth and can reduce flower and fruit production. And then there is also the need for much more frequent watering and fertilizing with a confined rootball and soil mass.

One always wants to err on the side of a larger container rather than a smaller one. Think about the spacing suggested for planting the same plants in the garden and extrapolate that to a corresponding container size. One would not normally plant peppers as close as 8", which is the diameter of a 2G container.

Thanks for the help on this. I have no problems using a 20 gallon pot except for the fact that you really can't move them once all the dirt is in. The root sizes compared to the size pot makes sense. I have seen beautiful peppers in small pots. Mine will be a little bigger because I assumed that they need to be in 10 gallon pots. I will try to get the smallest pot I can get away with, but not so small as to be stingy with the plants either. Thanks again.

For most tomatoes I'd go as big as you can get. But peppers will be happy in smaller pots - and ecstatic in 10 gal pots.

Good luck,
Dennis

I get good growth with 5 gallon buckets. Tomatoes,
Peppers, watermelon, cantaloupe, cucumbers, zucchini.
I need to update this pic bc my garden has doubled in
size since I took this.

I agree with Gardengal and DMForcier. Go big for most veggies in containers. I suspect most of the people who tell you you don't need to use such large pots for tomatoes have never grown an indeterminate tomato in a container for a full season. I've been growing tomatoes in 20- and 25-gallon pots for more than 20 years, and I've been using Smart Pots since 2008. I like them a lot better than regular pots.

Here's one of my tomatoes in a 20-gallon smart pot in June of last year, about six weeks after plant out. That's a six foot tall Texas Tomato Cage and the plant had already grown taller than the cage. It grew about two feet taller and almost two feet wider over the summer and produced dozens of tomatoes. I do think you can get by with a 5-gallon pot for most peppers, but some of the big bells and anaheims will grow better and produce more in a bigger pot. If you do searches on the tomato forum, you'll find that most of the experienced container growers recommend a minimum of 15 gallons for an indeterminate tomato. Remember that one big advantage of a larger pot is that you don't have to water as often. I water every other day during a heat wave.

- So, what do you do with bitter melon/bitter gourd? I have two seedling germinated and considering either planting them in the same 15 gallon fabric pot or in two separate ones.

- I agree about the container size at least for my location (Southern CA). Tried the 5 gallon ones and in our hot dry summer these tend to dry out and heat up too fast. Even tried those "topsy turvy" things (these "upside down" growers have about 2 or 3 gallon of soil and were $1 at the dollar stores) and they are even worse in this respect.

The tomatoes did grow and fruit in these smaller containers but not as well. So now I am almost exclusively going with 15 gallon and above for container tomatoes.

This post was edited by DHLCAL on Fri, May 9, 14 at 0:16

Ohiofem, those are the best cages I've ever used. Plus they store away so nicely.

Jerry