Starting Tomatoes From Seed: The Complete How-To Guide

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Starting tomatoes from seed can save money and it’s not difficult if you know the tools and steps to be successful. Give your young plants a head start using the steps and tips outlined in this post.

close up of a tomato seed germinating

Tomatoes for my Garden

It’s that time of year my friends. It’s still cold outside, but there are signs of spring all around. The robins have returned, the grass is starting to green up, and my tulips are just poking up their green sprouts above the soil.

I have already put my time in scouring seed catalogs and deciding which tomato varieties I will plant this year. The variety of tomatoes that are available to you when you start from seeds is exponentially larger than what is available at garden centers. I always plant a variety of different tomatoes in my garden. Cherry tomatoes, paste tomatoes, roma tomatoes and slicing tomatoes are all there. Some of my tried and true varieties are bendita, chef’s choice orange, sungold (or candy tomatoes according to my kids), amish paste and wood’s brimmer. It’s always fun to try some new varieties every year to mix things up.

Even though it’s still too cold and muddy to start planting anything outside in my garden, it’s the perfect time to start tomato seeds indoors. Tomatoes are a great fit for starting indoors and you don’t need much space to do it. Starting tomatoes from seed is not hard. If you have no experience starting tomatoes from seed, this post will help you understand all the supplies you will need, when you should plant seeds based on your last frost date, and how to keep your tomato plants alive and well for their extended stay in the house. Growing tomatoes from seed is not hard if you have the right supplies and you understand the process.

Basic tomato plant needs

close up of a pile of red tomatoes

When starting tomatoes from seed, you need to keep in mind their most basic needs. They need good soil, water, the right temperatures and light. That’s it! Some people tend to overthink this process and it is really that simple. Give tomatoes the right soil, the right amount of water, keep them warm, and give them plenty of light and they will thrive. Follow these steps and this fall you will be adding your own tomatoes to your delicious salad, BLT, or pasta.

How to start tomatoes from seed: Step-by-Step

  1. Gather your supplies. You will need seeds, pots, potting soil, watering trays, water, and some kind of grow lights system (more on that later). It’s also helpful to have some plant markers to mark your different varieties.
  2. Fill your pots with good quality potting soil all the way to the top.
  3. Use a permanent black marker to write the tomato variety and the seed source on a plant marker for each type of tomato seed you are planting.
  4. Place the plant markers in each pot.
  5. Place two tomato seeds in each pot by picking up two seeds and placing them gently on the soil surface.
  6. Gently push the seeds down into the potting soil about 1/8 inch.
  7. Cover the seeds with potting soil.
  8. Gently water each pot so that the potting soil is saturated. You can also add some additional water to the bottom of the watering tray.
  9. Place plastic wrap over the top of the pots and watering tray to keep the water inside. This will ensure that your seeds do not dry out before they germinate.
  10. Place your trays in a warm room or on a heat mat. The ideal temperature for germinating tomatoes is between 70 and 80 degrees F.
close up of tiny green tomato plants germinating in potting soil and white plant markers

When to start tomato seeds indoors?

The best time to start tomato seeds indoors 6-8 weeks before the last frost date in your area. This date will be different depending on your growing season. In my area, mid-March is the perfect time to plant tomatoes indoors. This allows me to plant the tomatoes outside around Memorial Day.

Is it better to soak tomato seeds before planting?

Tomato seeds are very small and delicate and susceptible to rot. For this reason I never soak my tomato seeds before I plant them. It’s always a good idea to keep your tomato seeds dry until you plant them.

How long does it take for tomatoes to start growing from seed?

If you keep your tomato seeds in a warm room between 70-80 degrees F, you can expect germination to happen in 5-7 days. Sometimes it might take up to 2 weeks, but if your seeds still haven’t germinated after 2 weeks, it’s best to replant them. They may have dried out, the room might have been too cold, or your seeds might be too old.

Do I need grow lights?

The short answer is yes! In my experience, grow lights are necessary for successfully starting tomatoes from seed. We want to avoid seedlings stretching to reach the light and it is pretty hard to give them enough light without some dedicated grow lights. This is especially important once the tomatoes grow their first sets of true leaves. Most of the time, placing your tomato plants in a sunny window will not be enough.

Caring for Tomatoes after Germination

Congratulations! You succeeding in getting your tomato seeds to germinate! Now it’s time to set them up for success growing indoors for the next 6-8 weeks.

Watering tomato plants

The best way to tell if your tomato plants need to be watered is to touch the soil with your finger. Push your finger into the soil about 1/2 an inch. If it feels wet, you don’t need to water. If it feels dry, add some water to the bottom of the watering tray. Never water tomato seedlings from the top. Check your soil moisture every 3-4 days.

Room temperature

If you used heat mats to help your seeds germinate, you can now remove them from the heat mats. You will still want to keep them in a warm location that is not cooler than 60 degrees F. Tomatoes are heat-loving plants and they will not grow well in a cold room with a low soil temperature.

Light

Tomatoes need plenty of light after they germinate. As soon as you see the tiny seedlings pushing through the soil, you need to put them under a light. Make sure the light is only 2 or 3 inches above the top of the plant at all times. As the plant grows, continue moving the light so that it stays 2 or 3 inches above the top of the plant.

I use my light system and my timer to leave the lights on my tomato plants for 20 hours a day. This can vary depending on the type of lights you are using and how close they are to the plants. If your plants are starting to stretch to get more light, then you need to either move the light closer, or leave it on longer each day. You will need to check on your plants every 3-4 days to make sure they are getting adequate light.

Potting up to Larger Pots

If your tomato plants become too large for their containers before it’s time to plant them outside, you may need to move them to some larger containers. If you do this, it’s best to bury as much of the tomato stem in the soil as your new pot will allow. The tomato plant will form new roots along this buried part of the stem and the plant will be very strong and ready to go outside in a few weeks.

Hardening Off

When it is time to plant your tomatoes outside, make sure you ease their transition by hardening them off. Place your tomato plants outside for 1 hour the first day, 2 hours the second day, and so on until they are outside all day. Make sure they are getting full sun during this process so they will be used to the sunshine when you plant them in your garden spot.

Essential Supplies

Seeds

Don’t underestimate the importance of choosing good quality tomato seeds! I like to choose as many heirloom varieties as I can. Growing heirloom tomatoes allows you to save seeds if you want to. You will not get the results you are expecting if you save seeds from hybrid varieties. There are so many varieties of tomatoes to choose from, so have fun picking your favorites!

seed packets of red tomatoes, green peppers, green tomatillos and purple tomatillos laying on seed starting trays filled with potting soil

Seed Trays

There are so many container options out there for starting tomatoes from seed. From egg cartons, to plastic pots, to peat pots, the choices are many. I have tried all of these options over the years with varying success. Just this year, I purchased seed trays from All About the Garden. The quality of these trays far surpassed my expectations. They are very sturdy and well designed and I’m sure I will be using them over and over for years to come. They have larger holes in the bottom which will contribute to better root systems. I couldn’t be happier with this purchase.

black plant pots sitting on concrete

Watering Trays

Its is critical to your tomato growing success that you water your seedlings from below. You don’t ever want the stem or leaves of your tomato seedlings to get wet as this will encourage fungus and disease to grow and possibly kill your seedlings. I use watering trays under my pots so that I can pour the water in the bottom of the tray and let the potting soil and plant roots uptake the water from below. The trays I use are very sturdy and can be reused year after year.

Potting Soil

There are so many seed starting mixes and potting soils to choose from it can become overwhelming to decide. I started out using seed starting mixes which are great for germination, but don’t always have any nutrients to sustain the plants after they start to get big. Because of this, I always had to start with very small pots for germination and then move the seedlings up to larger containers with some kind of potting soil. This was an extra step that I wanted to get rid of, so I switched to a organic potting soil 2 years ago and I have been very happy with the results. I have to grow my seedlings inside my house for 6-8 weeks and the potting soil provides all they need for that extended period without having to add any fertilizers. This soil is light enough to allow germination, but sticks together enough to not be a pain at planting time. It helps produce strong stems and healthy leaves.

a bag of G&B organics potting soil

Plant Markers

I always write the tomato variety and the seed source on plastic plant markers when I’m starting tomatoes from seed. This helps me to identify which varieties and seed sources worked best for me at the end of the season. When I plant the tomato seedling out in the garden, I move the marker out there too.

Light Stands

I have been using the same light stands for over 10 years now. They are 53 inches wide and 48 inches tall which gives me plenty of room to fit multiple trays. The width is just right for a 4 foot long grow light. These stands also allow you to adjust the height of the light which is critical for avoiding leggy seedlings!

Lights

Tomatoes plants need bright light to grow strong leaves and stems. I have been using basic shop lights from Home Depot for over 10 years. I have had success growing tomatoes with these lights and if they fit your price point, they are definitely the way to go. Just this year I upgraded to some dedicated grow lights. I’m hoping that the full-spectrum light will produce even stronger seedlings.

Light Timer

I have found outlet timers to be very helpful. They automatically turn on and off the power source which controls the amount of light I am providing to my seedlings. You just set the time you want the lights to turn on and off with these timers and then forget about it!

Heat Mat

If your house is not a warm place with a consistent temperature between 70-80 degrees F, heating mats can be placed under your watering tray to make sure the soil is warm enough for germination. I have had great results growing tomato plants in my unheated basement with heat mats under my watering trays. Tomato plants need to be in a warm location to grow well.

Go here to view and purchase products, supplies, and tools mentioned in this post.

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2 Comments

  1. Thanks for the info Halli! It’s super helpful and informative! My tomato seeds have germinated and I love watching them grow!

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