When available, choose varieties that are resistant or tolerant to a disease that previously has been a problem. If seed rot or damping off have been problems in your garden, then treating the seed with a fungicide will prove helpful. Begin with healthy plant material to help plants become quickly established in the garden. Plant materials that are unhealthy at the start never yield as much as healthy ones or may die while still young. Reputable seed companies sell only disease-free plant materials.
Some seeds are hot water treated to remove infectious agents.
Some are tested to reduce the risk of seed-borne viruses. When shopping for transplants or other propagating material, take time to thoroughly examine the plant stock to make sure it is healthy and vigorous. If you save your own seed, harvest it from healthy plants and dry it thoroughly. Store such seed in properly labeled airtight containers in a cool, dry place. A sunny area with well-drained soil is an ideal site for vigorous growth of garden plants.