Second, I live in Minneapolis, MN and I have seeded my tomatoes a little over a month ago but how do the green houses get their plants to grow so big? Do they plant their seeds in January?

No they don't start them extra early as a rule. Some commercial growers use growth stimulating chemicals on their transplants - something most of us would prefer to NOT use. Expensive and usually not available to the average grower anyway. But the main factors are all the light that is available in a GH that you simply cannot duplicate with the average indoor set-up for growing seedlings and the seed starting mixes they use. Not to mention that they don't over-water like most home gardeners do.

But for best results when it comes to transplanting, you don't really want really large transplants anyway - 6-8" is ideal. Granted you have a short growing season but that doesn't mean you can't work with that limitation. Lots of methods for extending that growing season work much better than just trying to transplant big plants.

Have you researched methods for extending the season? Using varieties with shorter DTM? Pre-warming soil, cold frame, using low tunnels, covering with a cloche or WOW for earlier planting in the spring? And in Fall row covers or temporary tent covers. All can add 6 weeks to your season and get you more ripe tomatoes.

I have always had trouble getting my tomatoes to bear fruit as well.

Excessive nitrogen and over-watering are primary contributing factors to that issue. Variety selection and its DTM can also contribute.

So give us more details on the varieties you use, exactly how you are growing them from seed, your light set-up and potting mix used, how you are watering your plants once transplanted to the garden, what fertilizer you use and how often, etc.

Dave

But more importantly they are still in small cell packs and should have been transplanted to individual containers sometime ago. They are rootbound and nutrient poor.

Commercial growers start 100's of plants in one of those black trays. Once germinated and while they still have only cotyledons or just barely developed true leaves they are transplanted to cell packs and planted deeply burying most all the stem. Once they develop 2 sets of true leaves they are transplanted again into 4" pots or larger (your employer's are in 16 oz plastic cups that many use).

Each transplanting stimulates more root development and the larger containers don't require watering nearly so often so the plants don't fade and yellow such as yours have.

Hope this helps.

Dave

PS: as for BTE and Mittleider, I'll bite my tongue on that issue.

Should I transplant the tomatoes or should I just wait to plant them in the garden?