Late Blight can wipe you out overnight. To grow without doing something to protect them doesn't seem to be possible anymore.
You have to keep all moisture off the plants themselves keeping the leaves dry at all times, this includes water that splashes up from the soil when watering. Some pick all the lower leaves off for this very reason. Hanging a plastic tent over them is one solution just make sure to leave the ends open for good air circulation.
Many around my area spray their tomatoes with a fixed copper solution every two weeks or so if they don't cover their plants. Good luck, it's really a sad sight to get up one morning to find all your tomatoes have sucumbed to blight.
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Also, lime (calcium)is essential.