Starting Tomatoes From Seed

Before planting, you will need to know your USDA Plant Hardiness Zone. “The plant hardiness zone is a geographic area defined to encompass a certain range of climatic conditions relevant to plant growth and survival.” This zone number will give you guidelines that correlate with your first and last frost dates in your area, allowing you to plan accordingly. With your grow zone information, you will be able to find your average last spring frost date. Using this date, count back 6-9 weeks for the proper planting time. This will give you a head start on the season and allow you to have established plants to put in the ground when the weather outside permits.

Here is a link to the USDA Hardiness Zone Finder:


Zone 6b

Average last frost date: Approximately June 1

Seed sewing date: March 30 - April 16 (6-9 weeks prior to last frost)

There are many alternative methods to sewing seeds; different containers to use, different mediums to plant in, etc., but for the sake of creating a basic guideline, I will keep it simple.


  • Tomato seeds

  • 16 qt bag of organic seed starting mix

  • Organic worm castings (optional)

  • Seed cells for planting

  • Drainage tray

  • Dome cover or large plastic bag

  • Heat mat

  • Grow light

  • Small fan

  • Plant labels

  • Organic water-soluble, all purpose fertilizer


  1. Pour your seed starting mix (and add a large handful of worm castings if using) into a bowl or bucket.

  2. Add a few cups of lukewarm water and mix well, removing any large twigs and breaking down chunks of mix at this time. The mix should be moist, but not wet.

  3. Fill your seed cells to the top and gently press down, to ensure there are no air pockets in the bottom of the cells. After pressing the soil down gently, there should be about a quarter inch of room at the top of each cell.

  4. Use a pencil to poke two small holes, side by side, at the center of each cell. The holes should be the depth of a pencil’s eraser. (Not deep)

  5. Plant 1 seed in each hole, totaling 2 seeds per cell, just in case one does not germinate.

  6. Cover gently, making sure all sides of the seed has come into contact with the soil.

  7. Label each pot promptly as it can be very easy to forget what was planted. Some use popsicle sticks, some use color coordinated markers and have a planting chart that correlates with their cells. Use whatever works best for you.

  8. Fill the drainage tray/water reservoir that your pots will sit in with approximately 1/4 - 1/2 inch of lukewarm water. You want to allow your seedlings to soak up water from the base of the pots like a sponge, rather than pouring water into the soil, which can potentially dislodge your seeds. Watering from the base can establish a stronger root system, prevent dampening off and can keep fungus gnats more at bay as the surface soil will remain dryer.

  9. Cover your seed cells/pots with a dome or use a plastic bag to wrap over your set up. This will help retain moisture, warmth and speed up germination. Note* Remove this plastic or dome a couple of times each day to offer air flow and to prevent algae growth and dampening off.

  10. Place your entire set-up on top of a heat mat or warm surface or at least keep it in a room that stays between 70-85° Fahrenheit. Tomato seeds do not need light until they have began to sprout.

  11. At the first signs of life, remove the dome or plastic bag promptly, even if only a few seedlings have emerged. The other seedlings will follow shortly if you are keeping the soil moist and the environment warm. If both seeds germinated, pinch out the thinner stemmed sprout.

  12. Immediately provide light to your seedlings. Place the light directly above your seedlings, as close as possible, without damaging your plants. Keep in mind that if your light emits high heat, they should be distanced further to prevent burning the sensitive seedlings or drying the soil out too quickly. Watch very closely the first few hours to see how the seedlings and soil react. If the soil dries up right away, the light may be too close. If the plants are reaching upward, the light is too far. The goal is to keep your lights close enough so they support your plants growing stout and strong, instead of leggy and weak.

  13. The hours of light you provide to your seedlings is a personal preference, but it is best to offer approximately 14 hours a day at minimum.

  14. Once your seedlings have began to sprout and are placed under the light, you will turn your fan on low and have it rotate back and forth. It should offer a light breeze, good airflow and gently vibrate the seedlings as they grow. This not only provides airflow and can help prevent dampening off, but also encourages the plants to root deeper, promoting stronger and hardier plants.

  15. Check the moisture of your soil daily and up to two times a day if you are in a hot and dry environment. Tomatoes do better in soil that is damp to somewhat dry versus overly wet. Practice a consistent watering schedule by pouring about a 1/2 inch of water into the reservoir when the soil begins to dry. The seedlings should not be sitting in still water regularly.

  16. Your plants will first produce cotyledons, which are the first leaves to emerge on a seedling. After approximately 2 weeks, you will see their first set of TRUE LEAVES emerge, which will look like tomato plant leaves. Some choose to feed their tomato plants immediately after germination, but I prefer to feed after the first true leaves have emerged. It is recommended to mix an all purpose, water-soluble fertilizer at half the recommended strength and feed the seedlings 1-2 times a week simply by pouring it into the reservoir in place of your normal watering.

  17. After around 4 weeks, when your plants are on their second set of true leaves, you will likely need to plant them into larger containers. We will go into our methods of potting-up in the following blog.

Happy Gardening!

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