How to Grow Tomatoes from Seeds

Nothing beats the taste of a vine-ripened tomato from your own garden. Starting tomatoes from seed lets you choose from more tomato varieties, gives you control over every step, and sets you up for an earlier, more abundant harvest.

Tomato Growing Timeline: From Seed to Harvest

The tomato-growing process is a series of simple but important steps. Each phase plays a critical role in giving you strong plants, heavy yields, and fewer problems along the way. Use the timeline graphic for a quick reference, and read on for what each step means in practice:

Choosing Tomato Types: Determinate vs. Indeterminate

Before you start seeds or pick plants, it helps to know which kind of tomato you’re growing. Tomato varieties fall into two main categories—determinate and indeterminate—and the difference affects how you care for them, how they grow, and when they produce fruit.

• Determinate tomatoes grow to a set height and then stop. They produce all their fruit over a short period, making them great for canning or batch harvesting. These are often called “bush” types and don’t usually need much pruning.

• Indeterminate tomatoes keep growing and producing fruit throughout the season until frost. They’re often taller and need support like staking or caging. These are sometimes called “vining” types and benefit from regular pruning.

How Long Until Your Tomatoes Are Ready?

How to Start Tomato Seeds Indoors

This section builds on what’s in the how to grow section above. Your heat mat and grow light are your secret weapons here—they mimic spring even if there’s snow outside. Follow these tips to give your seeds the best shot at a strong start.

1. Know Your Timing

Start seeds indoors 6–8 weeks before your average last frost. Check your USDA Zone Hardiness  to determine the right planting date.

2. Sowing Tips

• Use clean containers and moisten the soil before planting.
• Plant seeds ¼ inch deep.
• Cover with a humidity dome and place on a heat mat set to 70–80°F.
• Expect germination in 5–10 days.

3. Light Is Crucial

Once seedlings emerge, place them under grow lights for 14–16 hours per day. If using a window, rotate trays to keep seedlings growing straight.

What’s the best way to start tomatoes from seed indoors?

Use a Bio Dome or sterile seed-starting mix, a heat mat for warmth, and grow lights for strong, straight growth.

Note: Don’t direct sow outdoors unless you’re in Zones 9–11 and have lots of experience growing tomatoes from seed.

How to Care for Tomato Seedlings Indoors

Keep seedlings warm and well-lit. Water from below. Provide airflow to build strong stems. Think of seedlings like athletes in training—they need the right mix of support and challenge.

Thinning

If you’ve sown more than one seed per sponge or plug, wait until the first true leaves appear. Then, if two have sprouted in one cell, snip the weaker one at soil level. Don’t pull—it can damage the stronger seedling’s roots.

Watering

Keep the soil moist but not soggy. Water from the bottom or mist gently to prevent fungus and avoid disturbing roots.

Fertilizing

Once the second set of true leaves appears, feed with a diluted seedling fertilizer.

Hardening Off

About 7–10 days before transplanting, begin exposing seedlings to outdoor conditions. Start with 1 hour in the shade, and increase time and sun exposure daily.

Transplanting Tomato Seedlings Outdoors

Once you’ve hardened off your seedlings, it’s go-time. This is where spacing, soil temp, and support all come into play. Don’t skip staking—doing it early saves root damage later.

Transplanting Tomato Seedlings: Pro Tips for How to Do It Right

Once your seedlings are strong, hardened off, and the weather is reliably warm (nights above 50°F), it’s time to transplant. Here’s how:

1. Spacing

Determinate varieties(bush types): space 18–24 inches apart.

Indeterminate varieties(vining types): space 24–36 inches apart.

Leave 3–4 feet between rows to allow airflow and access.

2. Planting Depth

Tomatoes can be planted deeper than most plants. Bury the stem up to the first set of true leaves. This encourages roots to form along the buried stem, making for a stronger plant. If seedlings are tall and leggy, you can also plant them sideways in a trench—gently bend the stem and cover it with soil, leaving just the top above ground.

3. Prep the Soil

Choose a sunny spot with rich, well-draining soil. Mix in compost or a balanced fertilizer before planting. Tomatoes are heavy feeders. Avoid planting in the same spot you grew tomatoes or other nightshades (peppers, eggplants, potatoes) last year to prevent soil-borne disease.

4. Watering In

Water each plant deeply after transplanting to settle the soil around the roots. Keep soil consistently moist (not soaked) while the plant adjusts.

5. Support Early

Stake, cage, or trellis indeterminate varieties at planting time to avoid damaging roots later. Determinate types may still benefit from some support to keep fruit off the ground.

6. Mulch

Once plants are established, add mulch to help retain moisture, suppress weeds, and prevent soil splash (which can spread disease).

7. Pruning for Indeterminate Tomato Varieties

Pruning helps direct energy to fruit, improves airflow, and reduces disease risk.

How: Pinch off “suckers”—the small shoots that grow in the joint between a leaf and the main stem. These suckers turn into leafy stems that divert energy from fruit production. Remove them early when they’re small and easy to pinch.

Skip pruning on determinate varieties. They have a set growth pattern and need all their leaves to support a short, focused fruiting cycle.

Lower Leaf Pruning (Both Types)

Once your tomato plants are established and growing, it’s a good idea to remove the lowest leaves—especially any that touch the soil or look yellowed. This improves airflow, reduces the risk of soil-borne disease (like blight), and keeps the base of the plant dry. For indeterminate types, this is part of ongoing maintenance as the plant grows tall. For determinate types, limit pruning to just the lowest leaves—don’t remove too many, since these plants rely on all their foliage for a short, intense fruiting period.

Tip: Wait until plants are at least 12–18 inches tall before removing lower leaves. Always prune with clean hands or tools

When & How to Harvest Tomatoes

The harvest chart gives you general timing, but how do you know your tomato is truly ready? Go beyond the days-to-maturity with these tips:

• Check color and firmness
• Pick in the morning for peak flavor
• Avoid tugging—twist or snip

How do I know when my tomatoes are ready to harvest?

They should be fully colored and slightly soft to the touch. Snip or twist to avoid damaging the stem.

Use your visual reference to track timing, but let your senses guide your actual harvest.

With the right start, a little patience, and some sunshine, you’ll be harvesting baskets full of homegrown tomatoes in no time.