Starting Tomatoes from Seed Indoors (2023 Edition)

A lot has changed since we first began starting tomatoes from seed indoors. Yet, at the same time, not much has changed.

We are no longer using a makeshift plywood shelf, nor are we at our own home in Ohio. Instead, we live in Maryland with my parents, and are using basement shelving.

The amount and variety of seeds we are starting has also grown. We started with just one variety. Now we have about six different varieties for all our different tomato needs. Grape and cherry tomatoes for the kids and fresh salads, Hungarian Heart and Beefsteak tomatoes for slicing and canning as diced tomatoes, as well as San Marzano and Roma tomatoes for sauces and canning.

When to start planting.

Our garden zone is 6b. According to my father, and his father, the rule of thumb for planting is that you can start putting plants in the ground outside after Mother’s day. This year, Mother’s day falls on May 14, so I started the tomatoes indoors at about 6 weeks prior to the planting date on March 29th. Tomatoes need to be started earlier in the year so that they produce before the first frost.

How to plant tomatoes from seed.

You will find a lot of opinions on the best soil to use, whether you buy it pre-mixed from the store or create your own mix. We have found that using a good quality (aka name brand) potting soil (affiliate link) works really well, either organic or regular – it’s your preference. This year we used Miracle Grow Potting Mix. I was happy to read that Jill Winger from The Prairie Homestead shares this philosophy!

First I gather my supplies: Potting soil, a bucket and trowel (affiliate link) or paddle, a pitcher of water, Red Solo cups, scissors or knife, and my seeds. I like to start by getting my potting soil (affiliate link) damp. I just pour some into the bucket, add some water, and stir it up with the trowel.

Then I decide how many plants I want of each variety. To help my memory, I write the planting date plus the number of plants planted on each seed packet.

Once I know how many plants I will plant, I take the corresponding number of red solo cups, slice three holes in the bottom of each, and put them with their respective seed packet.

I work on each stack individually. Each cup gets about 1 inch or so of the damp potting soil, then 3 seeds from the seed packet. You will find the recommended planting depth on the back of the seed packet. These are 1/8th of an inch deep.

Once the seeds are planted, I make sure the date and variety of tomato plant is written on the side of each cup.

Once planted, the cups get put in a seed starting tray and placed on the shelf under the lights. I add water to the trays and then let them grow!

Thinning the seedlings.

When the seedlings are a few inches tall, you can start to thin them out. I like to leave the most mature and healthy looking seedling to continue growing. As they grow, continue to add soil to the cup – just make sure to not cover the leaves. For the seedlings that are removed, you can either replant them and share with friends, or add them to your compost pile!

Hardening off.

On nice spring days, a few weeks before the tomatoes are to be transplanted to the garden, you can start hardening them of. What this means is that you basically allow them to get used to the outdoors. It helps the stems become stronger so they don’t break or die because of the difference between the indoors and outdoors. We do this by bringing the tray outside for a few hours each day.

Time to plant!

Once your last frost date has past (click here to see what yours is), you can plant your tomatoes in the garden!