As I had mentioned in my previous column, some plant pathogens can be introduced into a crop on seeds. Bacterial pathogens are notorious for this means of dissemination. Purchasing treated seeds is one way to avoid this problem. The other way is to use hot water to kill diseases.
This treatment is suggested for seeds of eggplant, pepper, tomato, carrot, spinach, lettuce, celery, cabbage, turnip, radish, and other crucifers. Seeds of cucurbits (squash, gourds, pumpkins, watermelons, etc.) can be damaged by hot water and thus should not be treated.
To treat the seeds, wrap seeds loosely in a woven cotton bag, such as cheesecloth, or a nylon bag. Then, place the seeds in 100 degree water for 10 minutes. Next, place the pre-warmed sees in a water bath that will hold the water at the recommended temperature for the recommended length of time. Length of treatment and the temperature of water must be exact. A good thermometer and timer are important.
After treating the seeds, place the bag in cold tap water for 5 minutes to stop any heating action. Spread the seeds in a single, uniform layer on a screen to dry. Do not store the seeds until they are thoroughly dry so that they do not germinate or rot.
Here's the recommended water temperature and timing for several common vegetable: Brussels sprouts, eggplant, spinach cabbage, and tomato should be in 122 degree water for 25 minutes; broccoli, cauliflower, carrot, collard, kale, rutabaga, and turnips go into 122 degree water for 20 minutes; mustards and radishes are at 122 degrees for 15 minutes; peppers should be at 125 degrees for 30 minutes; and lettuce, celery, and celeriac are 118 degrees for 30 minute. Keeping the water too hot or keeping the seeds in too long will kill the seeds. Low water temperatures or shorter than recommended time periods will not kill the pathogens.