Recommendations for Starting Disease-Free Vegetable Transplants

Many home gardeners and commercial growers have placed their seed orders or have the seeds saved from last year safely tucked away. In the coming months it will be time to start those seeds in transplant trays. However, many vegetable growers start their seeds only to have them come up, wither, and die (Figure 1). Worse is when plants establish, only to become diseased after transplanting. The good news is that there are many steps that can be taken to prevent disease before it occurs. The following recommendations can prevent disease issues and aid in establishing a vegetable garden. While diseases may still occur once plants are transplanted, as a result of pathogens (disease-causing organisms) in the field, diseases are often less severe and growers suffer fewer losses.

Figure 1: Vegetable growers may experience frustration when seeds come up only to wither and die. (Photo: Michelle Grabowski, University of Minnesota Cooperative Extension Service)

Purchase disease-free seed

When purchasing seeds from suppliers it is important to note if seeds are certified disease-free. This means that these seeds have been tested and found to not be infected with diseases of concern. Information about whether or not seeds are certified disease-free can be found on seed packets or by asking your seed supplier.

Treat seed

Many home gardeners choose to save seeds from special varieties from year to year. However, pathogens may be present on the exterior and/or interior of seeds. This is also true of seeds that may be purchased but are not certified disease-free. In order to kill pathogens hot water seed treatment may be used for certain types of vegetables. In this process, seeds are placed in a water bath at 100°F to prepare them for the heat treatment. After five minutes, seeds are transferred to a second water bath and treated at a specified temperature, typically between 118 and 125°F, for a specified period of time. The temperature and treatment time varies depending on the type of seed being treated. Reference Cornell University’s Vegetable MD Online article entitled “Managing Pathogens Inside Seed with Hot Water.” There are certain types of vegetable seeds that cannot be heat treated, such as peas and beans. Often, these seeds can be purchased pre-treated with fungicide.

Surface sterilize transplant trays

Reused transplant trays can harbor pathogen propagules, which can cause seedling diseases. If trays are to be used again, they should be thoroughly cleaned with all soil and plant debris removed. After removing soil and plant matter, trays can be sterilized using a solution of one part household bleach to nine parts water (10% bleach). Pots and metal stakes can be sterilized in a similar way. Ensure that trays have been rinsed with fresh water and are completely dry before planting.

Pasteurize planting media

Planting media can also contain pathogen propagules that may infect seeds or seedlings. It is recommended to always use new planting media for starting seeds, and most purchased media is typically pathogen-free. If media is suspected of being infested with pathogens, pasteurization (heating up soil) can eliminate them. To pasteurize, put thoroughly moistened soil in a cake pan and heat at 200°F for 46 – 60 minutes, or put in a glass pan in a microwave oven for 15 – 20 seconds.

Additional Resources


By Kim Leonberger, Plant Pathology Extension Associate and Emily Pfeufer, Extension Plant Pathologist


Posted in Vegetables