Posted: 03/08/2012 at 10:28
If the problem was fungal, it had nothing to do with infected pots. Some bacterial and viral diseases can be transferred via previously infected soil and pots.
Can you post a photo? It would be interesting to see what the problem actually was.
Fungal disease is the most common ailment in the home tomato garden. You can't avoid fungal spores. They're airborne, invisible to the naked eye, and they're everywhere. Unless you spray preventively, there's nothing much you can do except undertake some basic housekeeping drills to try to minimise their impact.
Avoid wetting any foliage. Damp foliage is heaven for a fungal spore. Still air and clumps of foliage fall into the same category. Try to maximise air circulation by (1) keeping individual plants at least a metre apart, in fact as far apart as your growing space allows; (2) judiciously trimming foliage on individual plants to avoid walls of clumps of leaves; (3) remove the lowest branches of individual plants to maintain a gap of at least a foot between the lowest foilage and the soil. Fungal spores can and will fall from the leaves to the soil underneath and can splash back up again when watering. The gap between the lowest foliage and the soil helps against this.
In fact, you probably have more chance of dealing with disease outdoors than in a greenhouse. You need very very good ventilation to overcome the fact that the closed environment can be an incubator for disease.