Summer makes me think of fresh, ripe tomatoes. It is rewarding to pop a sweet cherry tomato into your mouth for a burst of flavour or to slice a juicy beefsteak tomato for fresh eating. Learn how to start tomato seedlings the easy way.

Solo cups filled with soil to start tomato seedlings indoors

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What are tomatoes?

Tomatoes are mostly thought of as a vegetable. In fact, most seed catalogues list them under “vegetable seeds”. However, they are not actually a vegetable at all. They are a warm weather fruit that is botanically an edible berry.

Tomatoes come in many sizes: large beefsteak tomatoes, medium slicing tomatoes, and cherry tomatoes. They also come in assorted colours from red to orange to yellow. There are even black tomatoes (they are really more a maroon colour!

Tomato seeds take anywhere from 7-14 days to germinate and take at least 60 days to mature. They are a warm weather crop, so they prefer warmer temperatures and will die at the first frost.

Why grow tomatoes?

As a Canadian homesteader, three reasons I grow my own tomatoes are:

The volume of tomatoes I need to feed my family for a year would be costly to buy at the store.
Tomatoes in the store have often been sprayed with a wax to preserve them.
Store-bought tomatoes lack taste and are not as nutrient-dense as homegrown.

At Groth Haus Homesteading we strive to eat as much organically grown food as possible (to avoid pesticides, herbicides, and waxes). As well, we want to reduce our grocery bill by growing the majority of the food our family eats in a year.

Homegrown tomatoes fill the gardener with such joy. Even a new gardener can grow them with ease. Begin by choosing your seeds.

How to choose your tomato seeds

First, choose your seeds based on what your family likes to eat.

Cherry Tomatoes: For example, my husband loves red cherry tomatoes. He eats them by the handfuls in his lunch daily during the summer months. A good variety for this are the Sweet Million cherry tomatoes. I like a cherry tomato that is a little bit larger, so I plant Red Zebra for myself.

Slicing Tomatoes: Another way to enjoy fresh tomatoes is by slicing them for sandwiches or salads. Some people enjoy the large Beefsteak types but my favourite is the Manitoba. It is perfect for our climate, matures in 65 days, and has medium sized fruit.

Paste Tomatoes: We preserve a lot of tomatoes for the winter months by canning salsa and pasta sauce. For this purpose, I prefer paste or Roma types because they are less juicy. When you are cooking down tomato sauce to it thick, less juice is better. A lot of people enjoy the Amish Paste. I’ve heard a lot of good things about San Marzano so I’m giving that variety a try this year.

Indeterminate or determinate tomatoes

Second, choose your seeds based on where and how you will grow them. Tomatoes come as indeterminate (vine types) and determinate (bush types). Indeterminate means they will grow and grow and climb and climb until the frost kills them. So these types need a trellis to support them. I grow my indeterminate Sweet Million and Pink Bumble Bee varieties inside my greenhouse using twine as their trellis.

Determinate tomatoes only grow to a determinate height so these are also known as bush types. These grow best using a tomato cage to help support the heavy fruit as it ripens. I grow these in my south-facing garden where there is lots of space for them to bush out.

Bush varieties also grow nicely in containers or hanging baskets. This year I’m going to try some Tumbler cherry tomato seeds and plant them in a hanging basket. The branches will droop over the sides with the fruit hanging like grapes. I will add some purple Lobelia to hang out with the red tomato berries.

When looking for seeds, I also like to focus on two other criteria: days to mature, and whether they are hybrid seeds or not.

I live in central Alberta where the growing season is only from end of May until the beginning of September, so I often look for seed varieties with “early” in the name. This is especially important for crops which have a longer time to maturity like peppers, tomatoes, and corn. However, early varieties can also be hybrids, which I mostly avoid.

Open Pollinated or Hybrid Seeds: Which one is for you?

West Coast Seeds has an excellent article discussing the difference between open pollinated and hybrid seeds.

If you’re like me and want free seedlings next year, you’ll want to choose open pollinated seeds this year so you can save seeds for replanting next year. I also find that open pollinated, which are sometimes referred to as heirloom varieties, often have more flavour. My favourites are: Manitoba and Red Zebra.

A hybrid tomatoes I have grown in the past was Early Girl. This variety matures in 57 days. However, I find when I am starting my seedlings indoors, I don’t need those extra few days and I prefer varieties where I can save the seed for future years.

Seeds can be purchased online or at most garden centers. Read the packages carefully to know what you are buying.

How many seeds do you need?

When calculating how many seed packets to buy, start by looking at how many seeds are in a package. For example, Red Zebra contains approximately 21 seeds. The package also says that 75% of the seeds will germinate. With that information, I know I have to plant about 1.5 seeds for every plant I want to grow.

Tip: sign up for emails from a few seed companies and you’ll be notified of their sales. A lot of online providers will offer an early-bird discount of 10% when you order in January. This is another great way to save money.

Begin keeping good records today

If you kept planting records last year, refer to that to see how many plants you grew. Do you need more, less, or different varieties? Did you preserve any tomatoes last year either by canning, dehydrating, or freezing? If so, what did you eat? What do you have left? That will help you know what to plan for this year’s harvest.

Keeping records will help your get better and better at this. If you’re just getting started, do a best guess as to how many tomatoes you’ll need for fresh eating and for preserving for the whole year.

Tip: an easy way to keep planting records is to take a free calendar (the kinds that banks and other business give out) and write your notes on it.

Days to mature: why we start tomato seedlings indoors

One of my seed choices is the Manitoba variety which takes 65 days to mature. Where I live, if I were to sow these tomato seeds outdoors at the end of May, they would not mature and bear fruit before my first frost in September. So, I germinate the seeds indoors and pamper the little babies until it gets warm enough to go outside.

Average Last Frost Date

You may hear a lot of talk about what gardening zone people live in. These are Plant Hardiness zones meant to help gardeners determine which perennial plant species to grow for their area. This would include fruit trees, berries and crops like rhubarb and asparagus.

Tomatoes and most garden crops are annuals and, therefore, we don’t go by hardiness zones for planting. Instead, we look at our average last frost date and the days to maturity on the seed package. Starting seeds indoors is an excellent way to extend my short growing season.

Where I live, in central Alberta, my average last frost date is May 20 (zone 9). However, I have had a killing frost as late as May 30. So I use May 31 (zone 10). This means I wait until May 31 to transplant my tomatoes seedlings outdoors.

Tomatoes need plenty of time to mature before they will bloom and set fruit. Most seed packets recommend starting indoors six to eight weeks before the last frost date, however I have found that my plants need 12 weeks. Therefore, to determine when you plant the seeds, I work backwards, 12 weeks from May 31, bringing me to March 8 as my planting date.

Save Time and Keep it Easy

t is common to start seedlings in a seed tray with 36 cells as pictured below.

However, when we start that way, we have to transplant the seedlings about 3 weeks after germination. So I prefer to start mine in bigger pots. I use Solo Cups. This saves a transplanting step and saves a ton of time!

Equipment needed:

Large Rubbermaid tote to mix seedling soil in
Coco Coir brick
Bag of Organic, sterile, potting soil or compost
Perlite (optional)
Bone Meal (optional)
Calendar or spreadsheet to record seeding dates and varieties
Trays without holes (to put the pots in)
Solo cups (to use as pots) I punch holes in the bottom to allow for drainage
Gloves (optional)
Hori Hori Knife (optional)
Clear plastic domes to put on top of the trays to make a greenhouse effect
Seedling heating mat or the Double seedling heating mat (recommended)

When I decided to expand my garden and seed more plants in the spring, I also decided that it was worth a little to invest in good infrastructure as I would be doing this for years to come and the return on the investment would be worth it. So, I recommend buying the best trays and pots you can afford. The flimsy ones will break after a couple of years, but the firmer ones are more expensive. For peppers, I prefer to start them in the Solo cups rather than the smaller starter cells. (I use red Solo cups for tomatoes and yellow for peppers.) This allows me to skip a transplanting step which saves me a ton of time.

You’ll also want to invest in some type of shelving system with lights. But you don’t need lights for a couple of weeks, so let’s get started on the seedlings.

Seed starting soil

Seeds are amazing. They are created with all the nutrients they need for the first two weeks after germination. All they need is water. So you can plant them in a mix with very little soil. In fact, most store-bought seed starting soil doesn’t contain any soil at all! It is mainly made from peat moss. It is also usually quite costly.

However, I’m going to teach you how to save money by making your own seed starting soil that also saves you time by skipping a transplanting step!

My easy soil mix requires a coconut coir block and a bag of compost or potting soil. The Spruce has an excellent article on the advantages of coconut coir.

You do not want to use garden soil or compost from the outdoors. That soil has microbes, seeds, fungus, and insect eggs in it. Those components are wonderful for outside as it makes for great biodiversity, but it is a very bad idea for indoor gardening. So, you always want to use a sterilized soil for your indoor planting.

I like mixing my seedling soil in a large Rubbermaid tote. First, add the coconut coir and soak with water as per the label’s instructions. Break up the outer parts, add more water to reconstitute it, and when the entire brick has crumbled, add the soil/compost. I like my basic seedling mix to be around 75% coconut coir and 25% organic potting mix.

To my basic seedling mix, I like to add 5% perlite to make the mix even lighter and have more ability to hold water. Again we’re not going for a soil mix that is full of nutrition. We want to mix that is light, holds moisture, and is easy for those little seedlings to push through to the top of the soil.

Finally, because I am skipping a transplanting step, I like to take Jeff at Ripe Tomato Farms tip to add a cup or two of bone meal to the mix to give those little roots an extra boost. This also buys me a bit more time between when the true leaves form and when and when I have to transplant the babies them into bigger pots.

Mix all the ingredients together using a Hori Hori garden knife (my favourite garden tool) or by hand. Make sure the mix is moist before filling the pots.

The easy steps to start tomato seedlings:

Fill the Solo cups about 1/4″ from the brim with your homemade seed starting mix (remember to ensure the soil is moist).
Using your finger, poke a hole in the soil about 5mm-1cm (¼-½”) deep.
Drop one tomato seed in the hole.
Pinch soil to cover the seed.
Because we know that the germination rate is about 75% for most tomato seeds, we will plant 1.5 times the number of plants we need. For me, I want to end up with 6 cherry tomatoes, 12 slicing tomatoes and 22 paste tomatoes. So I planted a total of 60 plants. If I end up with too many, that’s ok. I can give them as gifts to my friends who didn’t get their tomatoes planted early enough.
Water the seeds from the top. I use an old dish soap bottle for watering my seedlings.
Keep soil as warm as possible. I use a seedling heating mat to warm the soil as it speeds germination. The ideal soil temperature is 25-35°C (68-95°F). This will speed germination to about 7 days.
As per the package instructions, try to keep seedlings at least 10°C (50°F). Room temperature is fine.
Pour some water in the bottom of the tray. This is how you will water the plants from now on. From the bottom, not the top.
Cover with the clear plastic dome. This helps retain moisture and heat. (Remove the dome and the heating mat as soon as you see germination.)
Go record the date and the varieties you planted today.

Directions:

Fill the Solo cups about 1/4″ from the brim with your homemade seed starting mix (remember to ensure the soil is moist).

Poke a hole in the soil about 5mm-1cm (¼-½”) deep.

Drop one tomato seed in the hole.

Because we know that the germination rate is about 75% for most tomato seeds, we will plant 1.5 times the number of plants we need. For me, I want to end up with 6 cherry tomatoes, 12 slicing tomatoes and 22 paste tomatoes. So I planted a total of 60 plants. If I end up with too many, that’s ok. I can give them as gifts to my friends who didn’t get their tomatoes planted early enough.

Pinch soil to cover the seed.

Water the seeds from the top. I use an old dish soap bottle for watering my seedlings.

Keep soil as warm as possible. I use a seedling heating mat to warm the soil as it speeds germination. The ideal soil temperature is 25-35°C (68-95°F). This will speed germination to about 7 days.

Pour some water in the bottom of the tray. This is how you will water the plants from now on. From the bottom, not the top.

Cover with the clear plastic dome. This helps retain moisture and heat. (Remove the dome and the heating mat as soon as you see germination.)

I place my trays on my seedling shelf right away with the heat mat underneath them. However, until the seeds germinate and the little sprout breaks through the soil, they don’t need light. So you can keep the trays anywhere where it is warm. Right now, heat is more important than light.

Go record the date and the varieties you planted today.

In about 7-10 days, you’ll notice the tomato sprouts breaking through the seedling mix. At this point, remove the dome and the heating mat, and turn on the lights. You did it! You started tomato seedlings!