How To Sow Tomatoes From Seed To Grow Healthy Transplants

Whether you're a seasoned gardener or just starting out, this guide will provide you with all the tips and tricks you need to grow healthy tomato transplants from seed. Tomatoes are an incredibly versatile crop, perfect for canning tomato sauce, making bruschetta, or preparing salsas. Growing your own from seed is the best way to have high quality plants for your garden that will produce an abundant harvest. Plus, you gain access to thousands of unique tomato cultivars that you have to grow for yourself to experience.

Check out the video version of this guide on my YouTube channel:

When to Start Sowing Tomato Seeds

The key to successfully growing tomatoes begins with timing. Generally, you should sow tomato seeds 8 to 12 weeks before your last spring frost date. Using my own garden as an example, my last frost date is the second week of February, so I start my seeds in mid-December for a 12-week growing period. For gardeners in warm winter climates like mine in Florida, one can grow tomatoes over the winter as well. I plant tomatoes twice a year, at the end of January and again at the end of August or first weekend of September. 

Gardening conditions vary, so if your setup is less than ideal, expect an 8 to 12 week growing period. When planting into your garden, make sure to bury at least half of the stem. This will lead to a larger root system since roots will grow wherever the soil touches the stem. Therefore, aim for seedlings that are at least 10 inches tall, since half of that height will be buried. 

The Four Requirements For Successfully Sowing Tomato Seeds

The seed-sowing technique for tomatoes boils down to mastering four essential factors: soil, warmth, light, and fertilizer.

1. Soil: When sowing seeds, opt for a growing medium that is sterile and free of pathogens. This should also be fluffy to facilitate easy root growth. Look for seed starting mixes at your local store or create your own mix with equal parts peat moss or coco coir and perlite or vermiculite. This combination ensures a sterile, fluffy medium that allows for easy root expansion. If you use soil from your backyard or compost, know that it will have pathogens that could lower germination rates. However, if that's your only option, proceed by sowing more seeds than you need to compensate for potential seedling loss.

2. Warmth: Tomatoes are warm-season crops. Exposure to cold temperatures will stunt seedling growth, potentially causing permanent damage. Most likely, 12 weeks before your last spring frost will be during the colder months. Therefore, sowing seeds indoors or using an outdoor setup to keep them warm is crucial. If temperatures drop below 60°F, seedlings will struggle. Maintaining a greenhouse-like environment with a few heat mats can keep them warm and toasty. When sown in a warm environment, tomato seeds usually germinate within three days, and seedlings grow quickly, often ready for transplanting at 8 weeks.

3. Light: Tomatoes require at least 8 hours of full sun. Indoor windows typically don't provide this amount of light. If your seedlings appear to be leaning or growing unevenly, it’s a sign they aren’t getting enough light. Using shop lights or grow lights to provide ample light can make a significant difference. For example, I use Mars Hydro 3x3 150 watt grow lights (can get from Amazon HERE), which have shown better results than shop lights. These grow lights provide a broader spectrum of light, resulting in thicker stems and larger leaves. My tomato seedlings are ready to transplant between 6 to 8 weeks when I use Mars Hydro grow lights. They take longer, like 10-12 weeks when I use shop lights. 

4. Fertilizer: Fertilizing your seedlings is crucial for rapid and healthy growth. Opt for a balanced liquid fertilizer as it ensures nutrients are immediately available. For seedlings, mix fertilizer at half strength. Tomato seedlings germinate two small cotyledon leaves first, which are round and flat. The next two leaves are known as the first set of true leaves. They resemble mature tomato leaves. Start fertilizing when the first set of true leaves appear. Fertilize every week.

Growing tomatoes from seed opens up a world of varieties, each with unique flavors and uses. By mastering soil, warmth, light, and fertilizer, you’re on your way to growing the best tomato seedlings. Don't forget to share your own tips and tricks in the comments below. Check out my website for some of my favorite tomato varieties.