grow · Grow

How to Grow Tomatoes from Seed

Start tomato seeds indoors 6-8 weeks before your last frost date. Plant seeds ¼ inch deep in seed starting mix, keep soil moist and warm (65-75°F), provide bright light once sprouted, and transplant outdoors after hardening off when nighttime temperatures stay above 50°F.

Total time: 6-8 weeks
Difficulty: Easy

Ingredients

1 seed starting mix
1 heating mat
1 grow lights or south-facing window

Step by step

Start seeds indoors at the right time. Count back 6-8 weeks from your area's last expected frost date. This gives seedlings time to grow strong before transplanting. Check your local frost dates if you're unsure.
Prepare your seed starting setup. Fill seed trays or small pots with seed starting mix — never garden soil, which is too heavy. You need something that drains well but holds moisture. Set up grow lights or find your sunniest south-facing window.
Plant the seeds. Make holes ¼ inch deep with your finger or a pencil. Drop one or two seeds per cell. Cover lightly with mix and mist the surface. Don't bury them deep — tomato seeds are small and need to reach the surface quickly.
Keep them warm and moist. Maintain soil temperature between 65-75°F. A heating mat helps if your house runs cool. Keep soil consistently moist but not soggy — think wrung-out sponge. Seeds typically germinate in 5-10 days.
Provide light once sprouted. As soon as green shoots appear, give them bright light. If using grow lights, keep them 2-3 inches above seedlings and run 14-16 hours daily. Rotate trays if using window light to prevent leaning.
Thin and transplant to larger containers. When seedlings have their first true leaves (not the initial round seed leaves), snip weaker seedlings at soil level if you planted multiples. When plants are 3-4 inches tall, move each to its own 4-inch pot.
Harden off before planting outside. Start this process 7-10 days before transplanting. Set plants outside for a few hours daily, gradually increasing time and exposure to direct sun. Bring them in if temperatures drop below 50°F.
Transplant outdoors. Wait until nighttime temperatures consistently stay above 50°F. Dig holes deeper than the root ball — bury 2/3 of the stem, including some lower leaves. Tomatoes will grow roots along buried stem portions.

Tips & troubleshooting

Use a fan to create air circulation around seedlings — this prevents damping off disease and strengthens stems
Bottom watering prevents disturbing seeds and reduces fungal issues — set trays in shallow water until soil surface is moist
Pinch growing tips when plants are 6 inches tall to encourage bushier growth and more fruit production
Save seeds from your best-performing plants by fermenting them in their gel for 3-5 days, then drying on paper towels
Start more seeds than you need — germination rates vary, and you can always share extras with neighbors

Variations

Direct seeding outdoors. In warm climates with long growing seasons, plant seeds directly in garden beds after soil warms to 60°F. Cover with row covers if nights are still cool.
Starting in newspaper pots. Fold newspaper into biodegradable pots that can be planted directly in the ground. Good for gardeners who want to avoid plastic containers.
Winter sowing method. Plant seeds in milk jug containers in late winter and leave outside. Natural temperature fluctuations trigger germination when conditions are right.

Questions

Why aren't my tomato seeds germinating?: Check soil temperature first — cold soil is the most common problem. Seeds also won't germinate if they're too old (over 4 years), planted too deep, or if soil is too wet or too dry. Fresh seeds in warm, consistently moist soil almost always work.
When can I plant tomato seedlings outside?: Wait until nighttime temperatures stay consistently above 50°F and daytime temperatures reach at least 60°F. Cold soil and air will stunt growth or kill plants. In most areas, this means 2-4 weeks after the last frost date.
Why are my seedlings getting leggy and falling over?: Insufficient light causes stretching and weak stems. Move plants closer to grow lights or a brighter window. You can also bury leggy stems deeper when transplanting — they'll develop roots along the buried portion.
How deep should I plant tomato seeds?: Plant seeds ¼ inch deep — roughly twice the width of the seed. Deeper planting makes it harder for seedlings to reach the surface, especially in heavy soils.
Can I use regular potting soil for starting seeds?: Seed starting mix works better because it's finer textured and drains well while holding moisture. Regular potting soil often contains fertilizer that can burn delicate seedlings and may be too chunky for good seed-to-soil contact.