If you live in a cold climate and you want to get big tomatoes, there's really only one solutions: walls of water. These devices are simple pieces of plastic that you fill with water and put around your newly planted tomato plant. They are cheap and they can be used year after year. The walls of water provide insulation to young tomato plants, allowing them to survive down to 24F. Using them, you can get your tomatoes in the ground up to six weeks earlier than without them. This means you'll be eating tomatoes earlier, and for a longer period throughout the summer. If you're looking at your tomato plants now and you are not happy with the results, next year try using the walls of water.