Posted: 16/09/2014 at 08:05
Jill, your situation isn't as dire as you think. "Blight" has become a generic term for the various fungal diseases that can affect tomatoes. The most common in the domestic garden are Early Blight and Septoria Leaf Spot.
Your soil hasn't been poisoned, per se. In all likelihood, fungal spores will have fallen from the plants to the soil beneath. They can and will survive a winter on top of the soil. The danger in planting next season in the same, untouched soil is that watering the plants will splash the spores back up onto the new plants' foliage, thus infecting them.
For space reasons, I've planted toms in the same spot for a decade or more. Prior to planting in a new season, I turn over the soil very well, burying any spores. Underground, they can't do any damage. Then I refresh the soil on top. Any fungal problems I suffer during the new season will be the result of fresh infections during the season. Fungal spores are airborne, they travel on the breeze.