This is the first season that I've tried growing tomatoes and due to lack of space, I'm growing them in pots. I have several varieties of heirlooms growing. I've noticed that on a couple of plants, the base of the stems have bumps growing. Is this a disease or is this normal? Also, at the end of the season should I discard the plants or will they come back next season? I live in Southern Calif. in the valley where the summer has been hitting the 90's and the winters get into the 40's. Thanks.