Growing Tomatoes From Seed: A Step-by-Step Guide

This post may contain affiliate links. If you make a purchase through links on our site, we may earn a commission.

Why start your own tomato seeds when you can pop into your local nursery and buy ready-to-plant seedlings? The biggest reason is variety! Your local nursery may have a dozen or so varieties of tomatoes, but growing your own tomatoes from seed allows you to choose from hundreds of heirloom, hybrid, and open-pollinated varieties available through seed catalogs. Plus, starting your own tomatoes can save money, especially if you have a large garden. Below you’ll find in-depth advice and step-by-step instructions on growing tomatoes from seed.

Growing tomatoes from seed: Types of tomato seeds

When flipping through your favorite seed catalog, you’ll probably notice descriptions like ‘heirloom’ (or sometimes ‘heritage’), ‘open-pollinated’, and ‘hybrid’. Understanding the different types of seeds will help you pick the right tomato varieties for your garden.

• Heirloom – An heirloom tomato is an open-pollinated variety that has been passed down through the generations. The main reason to grow heirloom tomatoes is flavor! The fruits are packed with mouthwatering flavors seldom matched by hybrid varieties. Of course, heirlooms offer diversity, too — fruits in an assortment of sizes, shapes, and colors. Popular heirlooms include Cherokee Purple, Brandywine, Pineapple, and Big Rainbow. 
• Open-pollinated – When you sow seeds of open-pollinated tomato varieties you can expect plants that are the same as the parent. An open-pollinated variety may not be an heirloom that’s been around for decades, however, but rather one recently created by a tomato breeder. Dwarf Sweet Sue, Dwarf Caitydid, and Glacier are examples of open-pollinated tomatoes. 
• Hybrid – Hybrid seeds are the result of controlled pollination where the pollen of two varieties or species are crossed by plant breeders. These are listed as ‘F1’ varieties in seed catalogs. The seed of hybrids aren’t saved as they won’t usually come ‘true to type’. So, why grow hybrids? Most hybrids offer improved traits, like disease resistance, vigor, higher yields, earlier harvest, and uniform ripening. Sun Gold is a popular heirloom tomato with golden, cherry-sized fruits. 

Growing tomatoes from seed: Variety selection

Now that we’ve gotten some background on the types of tomatoes seeds, it’s time to crack open those seed catalogs. Be prepared to encounter dozens, if not hundreds, of tempting varieties. To learn more about the many awesome tomato varieties available to grow in your garden, check out Epic Tomatoes, the award-winning book by Craig LeHoullier.

But, with so many varieties to choose from, how do you pare down your list and decide what to grow? Consider these three questions:

1) How much space do you have? 

Tomatoes are categorized according to their growth habit: determinate or indeterminate. 

• Determinate varieties are best for small spaces and container gardens. They grow two to three feet tall with fruits that mature around the same time (perfect for canning or sauce!). They also mature earlier than many indeterminate tomato varieties. Most gardeners support determinate tomatoes with cages.
• Indeterminate varieties, also called vining tomatoes, are the big guys. They can grow six to eight feet tall, and continue to grow and fruit until frost. You’ll need to stake or support the vigorous plants. You can grow them in containers, but I’d suggest finding a large pot and supporting the vines securely with stakes or a trellis.

2) How long is your growing season? 

Tomatoes are also classified by how long they take to mature — early, mid-, and late-season. I find it helpful to refer to the ‘days to maturity’, which is how many days a variety needs to produce fruit from transplanting (not seeding) in your garden. In short-season or coastal gardens, opt for fast-maturing, early tomatoes, like Moskovich (60 days), Northern Lights (55 days), or Sun Gold (57 days). If you’d like to figure out the length of your growing season, check out this handy calculator on the National Garden Bureau website. 

3) How are you going to use your tomato harvest?

There are so many different types of tomatoes to grow in a home garden: slicing, paste, cocktail, grape, and cherry tomatoes for example. When I’m trying to decide what to grow, I find it helpful to consider how I want to use my harvest. Most of my tomato harvest is enjoyed fresh from the garden in sandwiches and salads, but I also make several batches of sauce for the freezer. Therefore I plant a mixture of types, including those for sauce, some super-sweet cherry or grape varieties, and beefy heirlooms for slicing. 

Step-by-step guide to growing tomatoes from seed:

Below you’ll find the 9 essential steps to know when you’re growing tomatoes from seed.

Step 1 – Sow seeds at the right time

Growing tomatoes from seed takes six to eight weeks from sowing to transplanting. Starting seeds indoors too early results in leggy, overgrown seedlings. I transplant my seedlings outdoors about a week after the last expected spring frost date. To find your exact planting date, take the last frost date for your region and count backwards by six to eight weeks. That’s when you need to sow your tomato seeds indoors. 

Step 2 – Use clean containers when growing tomatoes from seed

I start a LOT of seeds each spring and want to be able to use my indoor growing space efficiently. Therefore, I sow my seeds in plastic cell packs placed in 1020 seed trays or soil blocks. Cell packs and trays are reusable, have drainage holes, and I can cram hundreds of plants under my grow-lights. You can also use plastic pots or recycled clean yogurt containers, egg cartons, milk cartons, and so on. 

Step 3 – Use a high-quality seed starting mix

Give your tomatoes the right start by sowing the seeds in a high quality potting soil. Moisten the mix before filling pots or cell packs to avoid uneven wetting. These growing mixes offer good drainage and are a combination of materials like peat, vermiculite, and perlite. 

Step 4 – Plant seeds at the right depth

Tomato seeds are fairly small and if you plant them too deeply, they won’t sprout. Sow the seeds one-quarter of an inch deep, covering lightly with moistened potting mix. Label each variety with a wooden or plastic tag and the name written in permanent marker (trust me, you won’t remember which is which if you don’t label them).

Step 5 – Provide plenty of light

Sturdy, healthy tomato seedlings need lots of light. Too little light results in legginess where the seedlings reach and stretch, eventually flopping over. The ideal place to start seeds is under a grow light, where you control the amount of light. My grow lights are inexpensive, four-foot shop lights hung with chains on a wooden shelf. As the plants grow, I move the lights up so that they are always just a few inches from the foliage of my tomato plants. I leave the lights turned on for 16 hours a day, and have a timer that turns them on and off. You can also use a sunny window to start tomato seeds, but due to low sunlight conditions in late winter, expect some stretching. If you plan on making seed starting an annual event, consider investing in fluorescent or LED grow lights.

Step 6 – Maintain moisture when growing tomatoes from seed

Overwatering is one of the quickest ways to kill delicate seedlings, so keep an eye on soil moisture. It should be slightly moist, but not soaking wet. A spray bottle is a handy way to dampen soil. After planting, use a clear plastic dome or a sheet of plastic wrap on the trays or containers to maintain humidity. When you see green sprouts, remove all covers to allow air to circulate. If you have a seeding heat mat, use it to speed up germination, but turn it off when half of the seeds have sprouted.  

Step 7 – Provide adequate air circulation

As noted in the previous step, air circulation is important when growing healthy tomato plants. My grow lights are set up in my basement where there isn’t a lot of air flow and this could lead to fungal issues if I didn’t have a small oscillating fan in the room to move air. Having good air circulation also toughens up the stems and foliage of the seedlings helping ready them for outdoor growing conditions.

Step 8 – Feed the seedlings

Many potting mixes contain slow-release fertilizer to provide nutrients slowly over several weeks. These fertilizers don’t last very long and once the plants have two sets of true leaves, it’s time to supplement with an organic water soluble fertilizer. Apply it at one quarter of the recommended rate every 12 to 14 days. Carefully read all labels on potting mix bags and fertilizer containers, following the application advice.

Step 9 – Harden off tomato seedlings

You’ve reached the last step of growing tomatoes from seed! Once you’ve reached the final spring frost date, it’s time to harden off your tomato seedlings. Hardening off is the process where indoor-grown seedlings are acclimatized to the great outdoors. (Read more about hardening off tomatoes.) Start by putting the seedlings outdoors in the shade for a few hours and then bring them back indoors that night. Continue to put the seedlings outside, gradually introducing them to a few more hours of sun each day. After 5 to 7 days transplant them into garden beds or containers.

For more on seed starting and growing tomatoes, check out the following articles:

• Soil blocking: A better way to start seeds
• The best tomatoes to grow for canning
• Are grafted tomatoes good for the garden
• Growing tomatoes in raised beds
• Seeds versus transplants: Should you grow your own seeds or buy seedlings? 
• What’s the best way to grow seeds: grow-lights or a sunny windowsill?
• Three pitfalls of planting seeds too early!

Last thought: If you enjoy growing your own tomatoes from seed, you may get a kick out of this hilarious book, The $64 dollar tomato.

Are you going to be growing tomatoes from seed for your vegetable garden?