seedlings growing in Rockwool

How to pre-germinate Tomato, Pepper, and Eggplant Seeds

I like to know if a seed has germinated before it ever goes into soil or a piece of hydroponic Rockwool. There’s an easy way to know if you have viable seed and that is through a technique that simply requires a sheet of paper towel, a container with a lid, water and a consistently warm location 72ºF-76ºF.

seedlings growing in Rockwool


  1. Simply take a clean glass or plastic container that has a fitted lid that completely closes. Do not use a container that is aluminum or metal as it can interact with your seed believe it or not. (You essentially want to create a micro-environment that will keep moisture inside the container.)
  2. Take a small sheet of paper towel and cut to fit your container. You’ll want a piece of paper towel to cover both the bottom of your container as well as the top of your seed.
  3. Put the bottom paper towel into place into your container. Wetten the paper towel with spring water or dechlorinated water. (You can use tap water, but the other two options are more ideal — tap water is treated with chlorine which kills beneficial bacteria, so it could possible impact any beneficial bacteria on the surface of the seed.)
  4. Place the number of seeds you wish to germinate. It’s a good idea to add several extra seeds as it is rare to get 100% germination from typical seed packets. By law, seed providers are to test their seed and under ideal conditions, 85% of their seed must germinate in order to sell it to the general public. So factor in, worst case, that 15% may not germinate. If you get more seeds germinating than you need, these can be grown out and given as gifts to friends and family or donated to your local extension office who often has a team of volunteers called Master Gardeners that maintain public gardens.
  5. Place the second fitted paper towel sheet over the seed. It should immediately soak up moisture from the other paper towel. As far as moisture consistency, you’ll looking for the entire paper towel to be wet, but no standing water. Seeds transpire so they essentially need to “breathe”. The goal is to keep consistent moisture on both sides of the seed without letting them sit in water. Thicker seeds may need to be nicked, so if you’re unsure if your seed requires special treatment, you can check our reference sheet here. Tomato seeds are pretty straight forward and typically take 3-7 days to pre-germinate depending on the variety and the temperature conditions. Pepper seeds will swell up a bit before you see the root emerge. Eggplant seeds will also swell up a bit, but they will take the longest typically to germinate, so patience. Some can take 10+ days!
The seed that is circled in green is ready to gently transfer to soil or Rockwool using a sanitized tweezer. (To sanitize your tweezer, simply clean with rubbing alcohol.) The seed circled in yellow shows swelling and indicates that you should probably check it the next day as the root is getting ready to emerge. The other remaining seeds are slightly swollen showing that they are still in the process of germinating. Do not give up on seeds that are slower to germinate — sometimes they can take up to 10 days even when you are providing ideal conditions. Check moisture daily and if paper towel smells funky, swap out for a new paper towel and rewet and put back into germination chamber container.
is a photo showing germinated seed that has been placed into Rockwool (see number one below). If you are growing in a hydroponic growing system such as a Tower Garden or Aerogarden, you’ll want to place your seed in Rockwool instead of soil. (Coco Coir is also a good alternative growing medium for hydroponics or aeroponics assuming it has support to hold material together such as in a mesh net.)
I like to cover my seeds with vermiculite. Some hydroponic growers insist that this step isn’t necessary, but I like to make sure my seeds receive adequate moisture throughout these early stages of growth especially. Strong healthy seedlings, make for strong healthy plants. I use this process for peppertomato, and eggplant seeds and any seeds that are not super small. Remember, some seeds need light to germinate (like lettuce), so be sure to reference our cheat sheet under seed starting on before starting seeds to know if your seed needs light, no light, or if it doesn’t matter.
You can use the paper towel method on any seed. Here Bok Choy seed is swollen (gel white casing is swollen around seed with root emerging). It is at this stage you want to gently transfer it to soil or Rockwool with a sanitized tweezer.

Helping you learn how to grow your own food and how to use what you've grown for optimal health for yourself and those you love. We also offer our own line of homegrown seeds grown using organic practices.