Hot Water Seed Treatment when growing vegetables

An uncommon practice but one that we should be using more is the hot treatment of seeds before sowing. We will firstly cover the reasons behind it and then get into how it is done.

Making sure your vegetable seed is pathogen free is an important first step in preventing these diseases from being a problem. Hot-water seed treatment can eradicate, or at least reduce the level of pathogens in vegetable seed and is effective because hot water soaks into the seed for a brief time and kills disease-causing organisms without killing the seed itself. This treatment works best for small seed.

Treat only the number of seeds that you plan on planting. Treatment temperatures and durations will vary depending on the cultivar.

To effectively hot-water treat seed, use a water bath with temperature control. Alternatively, you can use a pan heated on a stove. You will need to use a thermometer to measure the temperature. Adjust the stove settings appropriately and submerge the seed completely to ensure a constant and uniform temperature. Water that is too hot may injure the seed; water that is too cold will not eradicate pathogens.

Use the following steps to hot-water treat seed:

  • Thoroughly soak and pre-warm seed in 37°C tap water for ten minutes;
  • Transfer seed to heated water for the crop-specific temperature;
  • Place seed in cold tap water for five minutes to end the heat treatment;
  • Spread seed out on a paper towel or screen to air dry;


Treatment temperatures and timings by crop:

Crop                                      Temperature [°C]                             Time [minutes]

Brussel Sprouts                                 50                                                           25

Broccoli                                              50                                                           20

Cabbage                                            50                                                           25

Carrot                                                 50                                                           20

Cauliflower                                         50                                                           20

Celeriac                                             47                                                           30

Celery                                                47                                                           30

Chinese Cabbage                              50                                                           20

Collards                                              50                                                           20

Coriander                                           52                                                           30

Cress                                                  50                                                           15

Cucumber                                           50                                                           20

Eggplant                                              50                                                           25

Kale                                                     50                                                           20

Kohlrabi                                               50                                                           20

Lettuce                                                47                                                          30

Mint                                                     44                                                           10

Mustard                                               50                                                           15

New Zealand Spinach                         48                                                           60

Parsley                                                50                                                           30

Pepper                                                 51                                                           30

Radish                                                 50                                                           15

Shallot                                                  46                                                           60

Spinach                                                50                                                           25

Tomato                                                 50                                                           25

Turnip                                                   50                                                           20

About the Author

Christoff Boltman is the Seeds for Africa / H2GRO Hydroponic specialist. Christoff has been growing hydroponically for the last 15 years and welcomes the opportunity to share his experience and knowledge with our customers. Feel free to pop in at our showroom and Christoff will be delighted to show you around and advise you on what would best suit your needs.