Q: I have kept a tomato garden in the same spot for five years. For two years, all of the plants have succumbed to various diseases. Is there anything I can clean the soil with?  

A: Once diseases have built up in a spot, it’s hard to get rid of them. One method would be to plant “non-kin” plants like beans, squash or peas in the spot for a few years before trying tomatoes again. If you have only a small garden plot, where this is impossible, try planting grafted tomatoes. These plants have an heirloom tomato grafted onto a disease-resistant rootstock. You can do the grafting yourself (xrl.us/tomatograft) or buy them already joined. I don’t know of local sources for grafted tomatoes but Territorial Seed (www.territorialseed.com) sells them.