Although there are many factors to consider in growing healthy tomato plants from seed, getting the seeds to germinate in the first place can sometimes be tricky. After 15 years of growing peppers and tomatoes for market, I’d like to share a few tips that have helped influence germination success at my farm.
1) Seed Viability Relative to Germination:
- Shelf life: Tomato seeds tend to last much longer in storage than most other seed (i.e., onions need to be purchased fresh every year). Just make sure they were stored properly (cool & dry) and you should have around a 4-5 year shelf life for tomato seeds. Pepper seeds are considered by most growers to have a 2-3 year shelf life. Fedco seed company puts out an informative chart on saving seeds, which includes estimates of shelf life for a range of vegetable seeds. Click here for Fedco chart.
- Storage: Humidity shortens the life of saved seeds more than any other aspect. Make sure seeds have wintered over in a cool and dry environment (such as in a tightly sealed jar in the refrigerator or freezer). Dry storage at less than 65 degrees F will give you good germination results.
- Vigor: A number of online gardening sites explain how to test a few of your seeds for germination before planting. Just be aware that even if your older tomato seeds germinate, if they are too old or shriveled they may have a scant supply of food stored in their endosperm and the plants may end up weak and/or stunted.
2) Seed sowing tips:
- Potting soil can sometimes be fluffy with air, but seeds need to make good contact with the soil in order to germinate. Moisten your potting soil before placing it in the flat or container, drop the flat on the ground from a few inches above the floor to settle the soil into the container cells, and then make sure your seed makes direct contact with the soil. I use a #2 pencil to lightly push the seed into the cell and then use the pencil to push a bit of soil over the seed with enough pressure to make sure it securely covered
- Very fine seeds do not need to be covered, just press them lightly into the soil. A few seeds need light for germination (check your seed packages for which ones).
- General rule of thumb is to cover seed to a depth of three times their size.
3) Water & Germination:
- Water must be available to the seeds in order for them to germinate, but some air must also reach the seed for it to absorb the oxygen it needs. I mix my potting soil with very hot water until it is damp but not soaking wet. A good test is to squeeze a fistful of your moistened soil, checking to see if only a few drops of water squeeze out rather than a stream.
- Check your flats daily to make sure they have not completely dried out. If they become too dry, moisten them gently with a spray bottle. Peppers, in particular, do not like to germinate in wet soil.
4) Timing & Temperature:
- The length of time it takes for your seeds to germinate is heavily related to soil temperature. Tomato seeds should germinate within 5-6 days if you can keep the soil temperature around 80º F. Peppers take a little longer with a little higher temperature (7-8 days at 85º F). Remember this is soil temperature, not ambient temperature.
- Speeding things along: I usually get germination earlier than the standard charts predict by placing bottom heat under my flats using 100-watt light bulbs (see this post for my seed-starting setup).
5) Special Germination Tricks for Difficult Seeds
- Pre-soaking seeds: Soaking seeds in warm water overnight before planting helps to soften the seed coat and speed up germination. Many seeds, even if it is not stated in their steps of seed germination, will benefit from pre-soaking. I don’t usually pre-soak tomato and pepper seeds, but I always pre-soak parsley, sweet peas and nasturtium seeds
- Scarifying seeds: This refers to the process of literally damaging the seed coat, usually by scratching the seed with sandpaper and then soaking in water. Some seeds (i.e., woody plants in the legume family) are so hard and well protected by their seed coat that the seedling is not able to break through it on its own. Tomato and pepper seeds do not need scarifying, but some of the larger seeds with hard seed coats would benefit from this.
I have been starting tomato and pepper seeds for market now since 1998. The book that I found to be most useful throughout my adventure is The New Seed Starter’s Handbook, by Nancy Bubel. This book is research-oriented, comprehensive, and provides the scientific rationale behind each method she promotes. For more thorough information on the tips offered in this post, I would highly recommend Nancy Bubel’s book.
More Details for Tomato Seed Germination
There are two other posts on this site that cover seed germination with more details: