I don’t believe that growing tomato plants from seeds is the best way for new gardeners to get into gardening (read my plea for new gardeners to buy seedlings for first year or two here). But, once you’ve mastered starting with sturdy seedlings and growing the plants on to full maturity, it’s a lot of fun to start growing from scratch, er, seed. It enables you to grow unique seed varieties that and enables you to start gardening long before the weather is good enough outside.
In order to successfully grow tomato seedlings inside, I recommend that you have the following equipment:
- Artificial light source (A sunny windowsill is not enough. More on this in Part 2), often referred to as “grow lights”
- Seed starting mix / seed starting compost* Many of these are coir or peat based. Most are now sold with some sort of fertilizer in them, but it is not necessary for this stage of the plant’s life.
- Small pots or a seed starting tray* with a plastic dome (sometimes called a humidity dome) to cover the tray/pots.
If you’re just starting out, you might find it most economical to buy a kit that comes with the celled tray, a tray underneath to catch water, and the plastic dome. They’re usually very easy to find at most big box stores from February until summer. You can also improvise; I like to reuse the clear plastic clamshells that salad greens come in (just be sure to punch drainage holes in the bottom, and set it on a tray to catch excess water).
Optional but very useful:
- Clean spray bottle*
- Heating mat designed for starting seeds* (do not use a heating pad designed for people)
Tomato seeds should be started about 6 weeks before you plant them outside, which is when there is no more danger of frost in your area. Where I live, that’s usually in the middle of May, so I count back 6 weeks from that and start my seeds near the beginning of April. The danger in starting them too early is ending up with very large plants inside while it’s still cold outside; finding enough space under your grow lights to keep them alive and healthy becomes a challenge.
Fill the trays with dampened seed starting mix (if the bag is dry when you open it, pour some water in, squish it around, close up the bag, and leave it for a couple hours).
If you are planting more than one variety of tomato, figure out how you are going to label the tray. Do not think that you will remember which is which. Believe me, if you do not label them now, you will not likely be able to tell them apart until the tomatoes grow and ripen.
Some people like to use wooden sticks, cut up pieces of vertical blinds, or store-bought plant labels*. My current system is to run a piece of tape along the edge of the tray, and label it with the initials of the various varieties I’m growing. It may not be decipherable to anyone else that reads it, but it works for me. Use whatever system works for you.
Place one or two seeds in each cell of the tray. If you only plant one seed, if it doesn’t germinate you’ll have an empty cell. If you plant two and both germinate you can eliminate one. If my seeds are a couple years old, I have other reasons to question their viability, or there are only a few left in a pack, I will sometimes put three in a cell.
Seeds need to be in constant contact with damp soil in order to germinate well. Use your finger to gently push each of the seeds into the seeds starting mix to ensure good contact between seed and soil.
Sprinkle more dampened seed starting mix in the top of each cell–enough to cover the seeds by about 1/4″ (0.5 cm) and then use a spray bottle filled with lukewarm water to ensure everything is moistened.
Cover the seed tray to create a humid environment.
Tomato seeds need bottom heat in order to germinate. If you have a seedling heat mat, place the tray on the mat, plug it in and leave it on until the seeds start to sprout. Some people place their tray on a warm spot on top of their refrigerator, or somewhere else warm in the house.
Tomato seeds do not need light to germinate. But once they start to sprout, they need light right away.
Check the tray every day and ensure that the seed starting mix stays damp (not wringing wet, but moist). If you see mold forming it’s too wet. This is not the time to go on vacation; if you will not be around to check the tray every day do not start seeds until you can be.
Condensation will form on the inside of the plastic dome; this is fine. If conditions inside the dome are too wet, prop the dome open a little bit, and then close it again once moisture levels are where you want them.
One day, you will check the tray and a miracle will have occurred:
Read Part 2 to learn how to care for your seedlings now that they have germinated.
*Disclosure: some of the links on this page are affiliate links, meaning, at no additional cost to you, I will earn a commission if you click through and make a purchase.