When to Start Tomato Seeds Indoors? – Tomato Planting Tips

Written by

William Golder


Dorian Goodwin

when to start tomato seeds indoors

Tomatoes continue to be one of the highest-selling cultivars in America. However, growing terms for these fruits are susceptible to a location’s frigid climate, so only a select region has easy access to cultivating them.

Since there are cold regions like those in Zone 5 and below, it makes the gardeners struggle to sow these heat-loving fruits. But good thing they can plant seeds inside their home to trick their short growing season.

So, when to start tomato seeds indoors? It is recommended to grow them 6-8 weeks before the last frost date and at a temperature of 70-80ºF.

Best Time to Start Tomato Seeds Indoors

1. Plant tomato seeds indoors 6-8 weeks before the last frost date.


Starting tomato seeds indoors is one effective way to plant them early, especially if you live in colder regions where they have a short growing season for tropical plants.

  • Find the last frost date of your region before starting seeds

It is essential to know what month and average day your last frost is in your area to avoid sowing them too soon, as it can affect their growth.

After all, our primary goal is not to plant early but to produce good crops by starting seeds at the ideal time. Therefore, plant seeds inside your home, sow them around 6-8 weeks before your average last spring frost.

For example, if you live in Ontario, California, you can start seeds indoors around January 4-27 since the average last frost in most parts of the state is on March 1-10.

However, living in the Southern Hemisphere is a little unusual because it has an alternate spring season that often starts in September. In contrast to the Northern part, where spring typically begins in March.

For instance, if you live in Melbourne, Australia, you can plant seeds indoors in July because the last frost occurs in early September.

Whether you live in the southern or northern part of the globe, this 6-8 week planting rule can help you establish good-rooted plants and produce the best fruit harvests.

  • Plant depending on your zone

The planting date for growing tomatoes from seeds indoors depends on which zone you live in as each sector experiences different climates. It means that frost dates vary per region.

With that, dates on when to start them will also differ. You can refer to the seed planting window of every region here:

  • For zone 3a: you can plant seeds indoors between the first and second week of April.
  • For zone 3b: you can start seeds in the middle of March to early April.
  • For Zone 4 states like in the Colorado mountain part: You can sow seeds between the middle of March and the first week of April.
  • For zone 5 areas like Northern Indiana: Start tomato seeds early to mid-March.
  • For zone 6 locations, like those in Massachusetts eastern area: Plant seeds indoors from the beginning to the middle of March.
  • For zone 7 places, like those in some parts of NC: Plant seeds from mid-February to early March.
  • For zone 8: You can plant them indoors from the middle of January to mid-February.
  • For zone 9 and 10: Start seeds halfway through January to mid-February.

Read more: When to plant tomatoes in colorado?

However, for the best tracking of the updated seed planting window, you can search an informative chart about the hardiness zones and frost dates online to determine if you are sowing them at the right time.

2. Sow tomato seeds at a temperature between 70-80ºF


Tomatoes should be nurtured in an ideal temperature so they can germinate well. They thrive best in mild conditions ranging between 70-80ºF.

Before planting them indoors, it is crucial to monitor the proper temperature because conditions below 70ºF can impede the germination process.

And, if you place them in exceeding low-temperature areas, like under 50ºF, sprouting will be impossible.

In contrast, planting them at high temperatures above 80ºF is also risky for your seeds. Too hot conditions cannot let them grow.

Therefore, it is essential to think ahead before you plant tomatoes indoors, like preparing a heat mat or placing them on top of the fridge to maintain the proper amount of warmth.

Tips for Start Tomato Seeds Indoors

  • Use clean plant cell packs or pots 3 inches in height to allow maximum growth for roots. Also, ensure to use the ones with drainage holes at the bottom.
  • Name every pot with the type of variety you are planting to avoid confusion, as most tomato seeds look the same. Also, ensure that the tags will not quickly rub out so that you can still identify them until they grow.
  • Use a soilless potting mix for starting seeds. It is lighter, more well-draining, and disease resistant than regular potting soil. Seed germinates best when placed on good ground.
  • Feed your seeds with a deliberate amount of water twice a day. Allow them to get wet but not soggy to prevent them from drowning.
  • Ensure to lay them in a room with the proper temperature as mentioned above (70-80ºF). To keep warmth, wrap the containers with plastic or other covering materials, effective for trapping the heat until they germinate.
  • Sow your seeds just below the surface of the soil and give them sufficient space from each other to prevent their roots from knotting.
  • Give your growing seedlings more space to establish their roots by transplanting them into a larger container once their first set of leaves sprouts.

Tomato Seed Starting Methods


1. Grow tomatoes on the windowsill

The most common way to start seeds indoors is to let them grow on a windowsill. Since tomatoes need sufficient sunlight, exposure to the sun provides the ideal heat they need for germination.

2. Start tomato seeds under grow lights

Another best alternative for sowing seeds indoors is to let them flourish under grow lights. This method is effective, as they provide lighting similar to the sun. Although it is artificial, it is helpful for seed germination.

3. Plant seeds inside a grow tent

Using a grow tent is one effective way for the healthy development of your tomato seeds because it can manage the proper growing conditions like the ideal heat and daylight they need inside.

4. Grow tomato seeds in a greenhouse

Sowing tomato seeds inside a greenhouse is helpful, especially for those who live in colder regions.

Since the greenhouse is convenient for absorbing the sun’s heat and storing it, your tomatoes will thrive because of the proper temperature inside. Along with that, it protects them from heavy rain and pest attacks.


Can you start tomatoes indoors too early?

No. Sowing seeds indoors over eight weeks before the last frost can encourage feeble seedlings. That is because tomatoes need at least 10 hours of sunlight a day and the daylight in winter is less than the required amount of what they need.

More so, prolonged growing periods in pots will force them to bring out blossoms and fruit. The risk with this is they will bear undesirable quality of crop and lesser yields.

How early can I start my tomato seeds indoors?

You can start your tomato seeds as early as two weeks before your average last frost date comes as long as you will plant them in a greenhouse. That is because the structure can stimulate ideal temperatures that can help them grow well.

However, if you don’t own one, stick to the 6-week rule rather than the 8th if you want to start a little earlier. Knowing how early to start tomato seeds indoors is crucial if you want to protect your tomatoes from the risk of improper planting time.


All seed starting methods work well for producing healthy tomato plants. But the key to successful indoor seeding is to plant them two months before the spring frost and when the weather is moderate.

Sow your seeds in the ideal type of soil and in sturdy pots to ensure their success. And remember to keep them moist to encourage the best germination.

Now that you know when to start tomato seeds indoors, there is now a guarantee that you can plant them at the proper time and expect plenty of harvests.

Besides, you also can refer to best time to plant tomatoes in other USA states such as Georgia, Virginia, Oregon and etc.

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