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Simple Tips for Germinating Heirloom Tomato Seeds Indoors

Simple Tips for Germinating Heirloom Tomato Seeds Indoors
Home » Grow Your Own Food » Growing Great Tomatoes » Simple Tips for Germinating Heirloom Tomato Seeds Indoors

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 20 years of growing peppers and tomatoes for market, I’d like to share a few tips that have helped influence germination success, especially with respect to heirloom tomato and chile pepper seeds.

Jump to:
Seed Shelf Life & Viability Factors
Keys to Planting Seeds Indoors
Speeding up Germination

Newly germinated tomato seeds
Newly germinated tomato seeds

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1) Seed Viability Factors 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 the longevity of seeds which includes estimates of shelf life for a wide range of vegetable seeds. 
  • 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 is recommended for 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)  Keys to Planting Seeds Indoors

How to Plant in Potting Soil

  • 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 seed types need light for germination (check your seed packages for which ones), but tomato seeds should be covered.
  • General rule of thumb is to cover seed to a depth of three times their size.

 How Much to Water:

  • 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.
Example of how soil should clump when preparing to germinate seeds
How soil should clump when preparing to plant tomato seeds

How Much Light is Required?

Heirloom tomato seeds and chile pepper seeds do not require light to germinate. In fact they do need to be covered with a bit of soil, and it is important to gently press the soil on top of them to make contact. The moist soil making contact with the seed is what stimulates germination.

Some of your seeds will germinate before others, so I usually put them under the grow lights when about 75% of the tray has germinated. Those that have not come up yet will be close behind and you don’t want the new seedlings to get leggy.

The lights can be on for 16 hours but it is good to give the new seedlings a rest also. I have found that th sweet spot is 16 hours under the lights and 8 hours in dark.

Robert Pirsig, author of Zen and the Art of Motorcycle Maintenance, observed that people need periods of doing nothing like plants need periods of darkness. “If a plant gets nothing but sunlight,” Pirsig said, “it’s very harmful. It has to have darkness too. In the sunlight, it converts carbon dioxide to oxygen, but in the darkness, it takes the oxygen and converts it back into carbon dioxide. People are like that too. We have to have some periods of doing and some periods of non-doing.”

3) Tips for Speeding up Germination

Using Bottom Heat for Seed Starting:

  • The length of time it takes for your seeds to germinate is heavily related to soil temperature.  Tomato seeds should germinate within 4-6 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).
Using 100-watt bulbs for heat source under seed germination trays
Using 100-watt bulbs for heat source under seed germination trays

Special Techniques for Particular Seeds

  • Pre-soaking seeds:  Tomato and pepper seeds don’t need to be soaked prior to planting. Some seeds with a hard shell do benefit from pre-soaking however. I always pre-soak parsley, sweet peas and nasturtium seeds overnight in warm water and find it speeds up their germination considerably.
  • 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.

Best book for details on seed starting
Best book for details on seed starting

Comprehensive Guides for Indoor Seed Starting

There are two other posts on this site that cover seed germination with more details:

Details for Growing Heirloom Tomatoes

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Margaret robinson

Sunday 30th of July 2017

Any advice for a newbie on the scene, bearing in mind that I'm in Australia, the seasons are back to front to the rest of the world. But we do have plenty of sunshine all the year round. It is now winter and I'm going to try growing my tomatoes on the window sill in my kitchen, similar to a hot house!! A lot of my veggies get eaten by possums, koalas etc. Im looking forward to starting my own tomato and capsicum (peppers) . I'm not very confident , so look forward to any advice. Thank you so much.


Monday 6th of March 2017

Have you planted Bradley tomatoes? If so do you have any tips you find useful? They are our favorite tomatoe and first year starting from seed. Thank you for all your advice and kind words!

God Bless!

Aleasea Smith

Sunday 26th of February 2017

When your plants get 4" high and are ready to be moved to bigger pots what type of soil should be used?

Friday 7th of October 2016

can i use a heater or lamp for my seeds?


Tuesday 26th of April 2016

I am growing onions from onions I bought that started growing green sprouts. How long does it take for the sprouts to grow

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