6oz just isn't big enough for a good root system IMO. My minimum would be a 4 inch pot but I like the 24oz yogurt/cottage cheese containers better. The roots still swirl around the bottom of those but they are easily teased free and far from root bound. 18oz sour cream containers might work ok. I'd definitely pot up from 6oz and I do use them for starting seed.

I grew seedlings in yoghurt cups once, but like Taz6122 says they are a bit small. If you want to save money, buy some large 18-24 oz disposable Styrofoam or opaque plastic party cups and use those. They are very cheap, also it is easy to punch drainage holes in them and write the name of the variety on the side. A lot of people use them; I guess the only disadvantage is that they might fall over if you are not careful when moving them.

...buy some large 18-24 oz disposable Styrofoam or opaque plastic party cups and use those. They are very cheap, also it is easy to punch drainage holes in them and write the name of the variety on the side....

I agree, not that they have to be Solo but I find both inexpensive to use. I start the seed in 3oz Solo bathroom cups and pot up at three weeks, then into 20oz Solo opague cups for the next 3-5 weeks. The base of their (Solo) 20 cup is larger in diameter so more stability, and by being able to see the sides I know when they are ready to set because I can see the root growth....

Actually, I think you are on the right track, just need a larger container. I use my cottage cheeze containers, but with a twist. I first take the cardboard core from toilet paper rolls, cut slits in the bottom so they can be folded in to make a container. This is easy to keep moist from the bottom and an ocasional spray.

Next, I take the cottage food container and cut the bottom out. Put the lid on and turn upside down. I transplant the seedlings into this when they have a couple of true leaves, burying the plant as deep as possible. As the plant grows, I add more soil until the top is finally reached. The good thing about this system, it is easy to take the lid off the bottom for transplanting. But the best thing is the roots have more room to grow in the wide base and will not get rootbound before being set out.
Carol

Depending on the weather I'll start with small yougurt cups transition to 18oz cups and if needed move once more to 1/2 gal milk/juice carton.

Moving to 18oz cups I'll place the seedling at the bottom and add mixture as the plant grows along the stem. By the time of my plant out the roots are now growing along the stem and at the bottom. Place the plant at a 45 deree angle in its final hole and watch it take off.