If you have a short growing season, it's important to start tomatoes early, indoors, so there is time to vine ripen. This is especially true if you are growing late season varieties. I start my tomatoes in early March. By May, they are in 1-gallon pots.
As seedlings, I fertilize once a week with fish emulsion. Once more established, I use fertilizer that is specific for tomatoes. The tomato fertilizer spikes work great, sorta like a slow release. I also add epsom salts every few weeks. This helps the plant to absorb and break down the nutrients. Promotes flower production and also bigger fruit.
Of course weather and temperatures are the biggest influence on tomatoes growing and ripening. But if you feed and water them regularly, you should have a great crop.
