When you pot up from whatever you started the tomato seeds in, you go up to a container that is only slightly larger than what they are in when you pot up. This is because going from a small container to a very large one puts tiny roots in a lot more soil with tons more moisture and it can be hard for them to adapt. Going up to the next size cup is better for the plant roots. I usually go from multiple seeds in each cell of a 72-cell flat to 5 oz. paper cups and from 5 oz. paper cups to 9 oz. paper cups. Often, the ones I am planting here at home go from 9 oz. cups into the ground if I can plant early enough. Otherwise, they go from the 9 oz. cups to 16 or 18 oz cups if I need to pot them up again and hold them a couple more weeks before planting them. Sometimes if I am behind on potting up I go straight from the starter flat to 9 oz. and from 9 oz. to 16 or 20 oz., skipping the 5 oz. cups completely. I start out with multiple seeds per flat in each cell, but when I pot up, I put two plants per cup. I leave them that way until after they are planted in the ground. I wait a few days for any disaster to hit and then I cut off the second plant at ground level, leaving whichever one has the stem with the biggest diameter.

After my plants are in the ground, then I pot up the leftovers to take to the Spring Fling. At that point, I move them to the largest cups I have---sometimes 20 oz. cups and other times 32 oz. cups. That's because my extra plants may have to grow on for up to a month between the time I pot them up and the Spring Fling. And, because I want for them to begin to branch out sideways as much as possible while crammed together in the plant flats, I cut off the second plant and leave only the strongest one in the large cup. Even if I do that just a week or two before the Spring Fling, it gives the single plant left in each cup more sunlight so it can begin branching out.

You can do it whatever way pleases you, but I've found that if I take smallish plants from small cups to suddenly being in really big cups, their growth stalls quite a bit, whereas it doesn't stall when I go up just to the next largest/slightly larger size of cup.

I'll be bringing two distinct sizes of plants this year---gigantic ones in big cups from the seeds sown on Super Bowl Sunday, and much smaller ones from seeds sown a month later that have been very slow to grow. I may leave them in their 5 oz. cups that they're still in, or if it is raining all day tomorrow, I might pot them up to slightly larger cups. That might depend on what size cups I have left in the potting shed.

One unique thing about tomato plants that sometimes baffles growers is that smaller plants often completely catch up with larger ones, whether they were planted the same time or weeks apart. I think this happens because as plants get larger and begin carrying fruit, some of their energy goes into the fruit and overall plant growth slows. So, by late May, nobody but me can look at my garden and know which tomato plants were 1' tall when they went into the ground in late March and which ones were 18" tall when planted in mid April and which late ones from the second or third round of late seed starting were 10" tall when planted in late April. By late May or early June, they all pretty much look the same. They will be about the same height (with some variation depending on each variety's typical maximum height) and width, and perhaps an experienced gardener could pick out the early plants by their heavier fruit load and larger fruit, but to the naked eye they all look the same. It doesn't seem like it would happen, but it does, every year.

Once the weather is exactly right in terms of air temperatures, soil temperatures and rainfall, a happy tomato plant can grow an inch a day. It is amazing. Inevitably that rapid growth does slow down when fruit starts enlarging and ripening, and it is a good thing. We don't want tomato plants so tall that we have to climb a ladder to harvest their fruit.

I see lots of plant pictures that have full massive vines, and I must do something wrong because mine never look like that. I always have tomatoes, but I don't have those huge multi-branching vines...unless it is Tess's Land Race. LOL

Sorry, I hit submit too soon. I planted one seed in a 3/4 inch soil block, then dropped those plants into a 2 inch soil block that had a 3/4 inch hole in the top. When they had at least 2 real leaves and were starting the 2nd set, I potted up to cups and into potting soil with some fertilizer. From there they went into the garden. Some years I pot up one more time, but this year I got a late start.

thanks i learn so much from all of you