When to Start Tomato Seeds Indoors

By: Chenell - Lead Writer and Gardening Advocate

There’s nothing like eating a homegrown tomato picked right off the vine in the middle of summer.

But tomato plants can take a while to get to the stage where you are harvesting their fruit, so many gardeners like to start their tomato plants indoors. That way, when the ground warms up and the spring temperatures are consistently above 50 degrees Fahrenheit, they already have a decent-sized plant to put in the ground and keep growing.

When to Start Tomato Seeds Indoors?

The best time to start tomato seeds indoors is around 5-6 weeks before your last frost date. While the seed packets might say 6-8 weeks, I have found that Mother Nature can often delay that timeframe by a couple of weeks, and then you’re in 1 of 2 positions:

  1. Your plants have to grow indoors for another few weeks, often getting to be way too big for the pots they are in. You can end up with rootbound plants, wilting tomatoes, and not enough space to keep them all happy inside anymore.
  2. You plant them outside after they’ve been inside for 8 weeks and then the weather turns frigid again. This leaves you struggling to figure out if you should dig them up and bring them back in or buy some protective row covers and hope for the best.

In my opinion, neither of those is ideal, and I’ve seen so many posts in Gardening forums about the stress that can come with both situations.

For those reasons, I like to play it safe and plant them inside around 5-6 weeks before the last frost date for my area. If I end up with tomatoes that aren’t as big as I wanted them to be when I transplant them outside, then so be it. But at least they are alive and I saved myself some stress.

What is the Best Temperature To Germinate Tomato Seeds?

According to the University of California, the best temperature to germinate tomato seeds is between 65-85°F. The minimum temperature is 50°F, and anything below that your germination rate will decline drastically. Any temperature above 95°F and the seeds will dry out and crack, leaving you with minimal viable seeds, if any.

What Month Do You Start Tomato Seeds?

The best month to start tomato seeds is going to vary by region, but oftentimes it’s around March-April. Here is a seed starting chart for tomato seeds broken out by Hardiness zone:

Tomato Seed Starting Chart (By Zone)

Last Frost Date (approx.)Start Seeds Indoors
Zone 1May 22 – June 3April 10 – April 22
Zone 2May 14 – May 23April 2 – April 11
Zone 3May 1 – May 15March 20 – April 3
Zone 4April 2 – May 13February 19 – April 1
Zone 5April 6 – April 29February 23 – March 18
Zone 6April 2 – April 22February 19 – March 11
Zone 7March 22 – April 4February 8 – February 21
Zone 8March 13 – March 29January 30 – February 15
Zone 9February 5 – February 26December 25 – January 15

Can You Start Tomatoes Indoors Too Early?

Yes, you can start tomatoes indoors too early. What can happen if you start them too early is that they either get really big inside before you’re able to plant them outside. The roots might become rootbound, you don’t ahve enough space to up-pot them into bigger containers, or you’re forced to plant some outside before the ideal temperatures and you lose some of your plants.

None of these are great options, so I always recommend not starting tomatoes inside any earlier than 6 weeks before your last forst date. This gives you a little wiggle room if the weather doesn’t cooperate, and often it doesn’t.

Do Tomato Seeds Need Darkness to Germinate?

Tomato seeds don’t necessarily need light to germinate, but they don’t need darkness either. It’s always best to have them in a spot that has enough light to grow past the germination phase. Otherwise, you might end up waiting too long to check on them and they can end up getting leggy with weak stems trying to find some sort of light.

Should I Soak Tomato Seeds Before Planting?

There is no need to soak your tomato seeds before planting. While some thicker seed husks like sunflower and some peas do better when they are soaked, this is not neccessary for tomato seeds.

What Do You Do After Tomato Seeds Sprout in a Paper Towel?

If you’ve successfully germinated tomato seeds on a paper towel, you can go ahead and transplant them into some potting mix to keep growing indoors, or plant them in the ground if the conditions are right.

Is It Too Late To Start Tomato Seeds Indoors?

Starting seeds indoors can drastically increase the length of the growing season, especially for fruiting plants like tomatoes and peppers. But you don’t have to start seeds indoors to have a successful garden season.

Even if life got in the way (or you forgot to start plants), you can always plant seeds directly into the ground once temperatures are consistently about 45-50 degrees at night.

As the saying goes, the best time to start your tomato plants was yesterday, the next best time is today!…or something like that 🙂

Don’t let fear of it being too late stop you, go ahead and plant some seeds and see what happens!



Hi - I'm Chenell! I lived in the city for almost a decade, but after moving to the suburbs in 2020, I decided the logical millennial thing to do was to learn how to grow my own avocado toast. That's what this site is all about. 🥑

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