What size pots?
I plant mine in 5 gal planters (deeper than they are wide because they need a lot of depth for the roots). I'd say 5 gal is the minimum size but I see pictures where people have had good results with smaller pots. I also have much better results with pots that have some sort of water reservoir at the bottom. Some of my pots have an external opening to fill from (my favorite) and some just have a reservoir that fills by trickle down through the soil. You want to make sure there's an escape route for excess water so the roots don't stand in water. Mine have a seam about 2-3 inches from the bottom for overflow.
How do I pot them?
Since I garden on a balcony I try to minimize weight as much as possible. I put 3-4 inches of torn up styrofoam packing material and packing peanuts (not the biodegradable ones made of cornstarch that dissolve in water) in the bottom for extra, light weight drainage. Lasts for years and doesn't go in the landfills. My potting mix is about 1/3 commercial grade potting soil, 1/3 peat moss for aeration, lightness and water retention and 1/3 compost of some kind. This year I'm using cotton burr compost and my plants seem to love it. Perlite for the same reasons as the peat moss - a couple of cups per 5 gallons. I also mix in 1-2 cups of slow release fertilizer pellets. I have a 20 gallon tub that's used for storage most of the year, but in the spring it's a mixing tub. Before I plant I empty the soil from the pots and remix just like I was starting from scratch (adding 1/3 each of peat moss and compost to enrich the soil - maybe less perlite although the little light weight pellets work their way to the top of the soil and wash away). At the bottom of each planting hole I add a handful of Epsom salts (something my grandmother always did!) - and next year I'll add a handful of lime with a couple of inches of soil on top of that before putting in the plant (it gives the roots something to grow for *G*). Be sure and strip the bottom limbs off of your little tomato plant and plant it deep (roots grow off the buried stem for extra vigor and strength).
Someone asked 'how high' should the plants grow?
That depends on so many things. The type of plant for one thing, the size of the pot, constant *regular* supply of water, growing medium, fertilization, weather, etc. Until this year my average tomato plant height from top to soil was about 4-5 ft. My heirloom Black Krim is a whopping 6 1/2 ft. I also have a Patio Tomato that's only about 2 1/2 ft. The seed packet or catalog description should give you an approximate height, but I've found that container grown ones don't usually get as big.
Tending during the growing season.
Absolutely as much sun as they can get is critical. With partial sun you might have a nice plant, but fruit will be smallish and more scarce. Regular watering. Don't let the soil dry out completely. It dries up the roots and makes it nearly impossible for them to take in the proper moisture. I fertilize once a week with just an all purpose liquid fertilizer - about 1/2 strength of what the label calls for if it recommends less frequent feeding. After the plant starts growing, strip off the limbs from the bottom 5-6" of the stem to keep them free of the ground. They won't produce anyway and they'll just suck water and food. Ditto for the *suckers*, those tiny limbs that start growing in the V of 2 other limbs - they just divert water and nutrients and make your plant bushy. Next year I'm going to try selective pruning and limit the number of limbs on one of my plants like some books recommend and see what the results are. In another week or so I'm going to scatter a handful of lime on the surface of the pots and water well to dissolve it.
a). If you're seeing a lot of blossoms but no or very few fruit, the blossoms aren't maturing into fruit for one reason or another - look in your garden shop for a 'blossom set' product. b). If you have a ton of small tomatoes that never get very big and you want big ones, either keep the blossoms plucked down to fewer or pull off small tomatoes so the plant feeds more nutrients to fewer fruits. c). If your tomatoes develop big brown spots on the bottom of the fruit you have blossom end rot which can be attributed to uneven watering or not enough lime in the soil. The bag of horticultural lime I bought this spring for $5 is going to last me for probably 3 years and it dissolves almost immediately with watering (follow the directions on the bag) and I had pretty spectacular results. d). Give your plants room to breathe, don't jam them too close together. That tends to breed disease and pests. If I were growing at ground level mine would be too close together. As it is, in my area and on a 3rd floor balcony, air circulation isn't a problem. e). Tomato cages! I am so investing in them next spring! I have a feeling they'll make my gardening life so much easier. f). Cracks in the skin can mean uneven watering. Some fruit are more prone to cracks than others. My Black Krim are very cracked on the shoulders but extremely healthy otherwise. These are 'dry cracks' - they've been growing with the fruit all along. I've had tomatoes that have suddenly split into 'moist' cracks after they've started ripening, like they got a giant grow spurt and began growing out of their skins. These I pick immediately. They'll draw pests and rot.
All of these tips seem to work damn well on my peppers, too.
These are just the things that work for me. What works for you?
As always, cross-posted so sorry for the spam.