When to Start Tomato Seeds Indoors by Zone

Start tomato seeds indoors 6 to 8 weeks before your average last spring frost date, then transplant outside 1 to 2 weeks after that date, once nights stay above 50°F. In practice that means mid-January to February in the Deep South (zones 8 and 9), late February to March across much of the middle of the country (zones 5 to 7), and late March to mid-April in the far North (zones 3 and 4). Your USDA zone gives a rough starting window, but your local last frost date is what you should count back from. The chart and steps below show exactly how to pin down your sowing date.

Part of our Vegetable Gardening & Raised Beds guide →

In this guide

1. Why 6 to 8 Weeks?
2. Zone-by-Zone Tomato Seed Starting Chart
3. How to Calculate Your Exact Start Date
4. Adjusting the Timing
5. Match Varieties to Your Season Length
6. Signs You Started Too Early or Too Late
7. Timeline From Seed to Garden
8. Can You Direct Sow Tomatoes Instead?
9. Growing Tomatoes Indoors Year-Round
10. Frequently Asked Questions

Why 6 to 8 Weeks?

Tomato seeds germinate in about 5 to 10 days at a soil temperature of 70 to 85°F. From there, seedlings need roughly five to seven weeks to grow into stocky transplants 6 to 10 inches tall with several sets of true leaves, which is the ideal size to move outdoors. Add a week for hardening off and a week of buffer after your frost date for the soil to warm, and the 6- to 8-week window follows naturally.

Tomatoes are frost-tender and sulk in cold soil. Planting them out early rarely gains you anything, because plants sitting in 50°F soil barely grow, and a late frost can kill them outright. Starting seeds earlier than 8 weeks usually backfires too: seedlings outgrow their pots, become leggy under limited indoor light, and may even start flowering before they are in the ground.

Zone-by-Zone Tomato Seed Starting Chart

The dates below are typical averages. Frost dates vary widely within a zone, depending on elevation, distance from the coast, and whether you live in a city or a frost pocket. Use this chart to get in the right range, then refine it with your own frost date.

USDA zone	Typical last frost range	Start seeds indoors	Transplant outdoors
3	Mid-May to early June	Late March to mid-April	Early to mid-June
4	Early to late May	Mid-March to early April	Late May to early June
5	Late April to mid-May	Late February to late March	Mid to late May
6	Mid-April to early May	Mid-February to mid-March	Early to mid-May
7	Late March to mid-April	Late January to late February	Mid to late April
8	Mid-March to early April	Mid-January to mid-February	Late March to mid-April
9	Late February to mid-March	Late December to mid-January	Mid-March to early April; also a late-summer start for fall
10	Frost rare or absent	Late summer for fall and winter crops; December to January for spring	September to October; February to March

In zones 9 and 10, summer heat is the real limit. Tomatoes stop setting fruit when daytime highs stay above about 90°F and nights stay above about 75°F, so gardeners there often grow two crops: one started in winter for a spring harvest, and one started in mid to late summer for a fall harvest.

How to Calculate Your Exact Start Date

1. Find your average last frost date. Look it up by ZIP code through your state’s cooperative extension service or a frost-date tool based on NOAA climate data. Note whether the date is a 50 percent or a 10 percent probability date; the later, safer date is better for tomatoes.
2. Count back 6 to 8 weeks. Use 8 weeks for large beefsteak and late heirloom types, and 6 weeks for cherries, early varieties and determinate patio types.
3. Mark your transplant date. Plan for 1 to 2 weeks after the last frost date. Watch the forecast for nights consistently above 50°F.
4. Schedule hardening off. Begin 7 to 10 days before transplanting.

Worked example

Say your average last frost is April 25 (typical of parts of zone 6). Counting back 8 weeks gives February 28, and 6 weeks gives March 14. Sow beefsteaks around the first of March and cherry tomatoes around mid-March. Begin hardening off in late April, and transplant in early to mid-May once nights stay above 50°F.

Adjusting the Timing

Start a little earlier if

• You grow under strong LED grow lights and can pot seedlings up into 4-inch or larger containers.
• You will use season extenders such as wall-of-water cloches, row covers or a cold frame, which let you transplant a week or two before the usual date.
• You are growing late, large-fruited heirlooms that need a long season.
• You have a heated greenhouse.

Start a little later if

• You rely on a sunny windowsill, where light is weak and seedlings stretch.
• Your spring is typically cold and wet, delaying soil warming.
• You want to grow transplants in small cells without potting up.
• You are growing quick cherry or early varieties such as those maturing in 50 to 60 days after transplant.

If you miss your window, do not worry. A seedling started two or three weeks late still produces well, especially in areas with long summers. You can also buy transplants from a nursery for the earliest crop and start your own seeds for later plantings.

Match Varieties to Your Season Length

Seed packets list “days to maturity,” but for tomatoes that number almost always counts from transplanting, not from sowing. Add the 6 to 8 weeks of indoor growing to get the true seed-to-harvest time. That matters most in short-season areas.

• Zones 3 and 4: the frost-free season can be under 120 days. Favor early varieties rated around 50 to 70 days from transplant, cherry tomatoes, and compact determinate types. Big beefsteaks rated 85 days or more often run out of season.
• Zones 5 to 7: most varieties work. Mix early types for a first harvest in July with mid- and late-season slicers and heirlooms for August and September.
• Zones 8 to 10: the challenge is heat, not frost. Choose heat-setting varieties and time sowing so plants flower before midsummer temperatures stall fruit set.

A practical approach in any zone is to sow two batches about two weeks apart. If the first batch gets leggy or a cold snap delays planting, the second batch is right on time, and any extras make good gifts for neighbors.

Signs You Started Too Early or Too Late

Sign	What it means	What to do
Tall, thin, pale stems	Too little light, often combined with an early start	Lower grow lights to a few inches above plants; run a fan; pot up deeper
Roots circling the pot, yellow lower leaves	Outgrowing the container before transplant time	Pot up into larger pots; feed lightly
Flower buds before transplanting	Seedlings are too old for their pots	Pinch off flowers; transplant as soon as safe
Tiny seedlings at transplant time	Started late or grown too cool	Hold a week longer indoors, or plant out and protect with row cover

Timeline From Seed to Garden

• Week 0: sow seeds a quarter inch deep in moist seed-starting mix; keep at 70 to 85°F, ideally on a heat mat.
• Week 1 to 2: seedlings emerge. Remove heat, move under bright light for 14 to 16 hours a day, and keep air temperatures around 65 to 75°F.
• Week 3 to 4: first true leaves appear. Thin to one plant per cell and begin weak fertilizer.
• Week 4 to 6: pot up into 3- to 4-inch pots, burying stems deeper to build a stronger root system.
• Week 6 to 7: start hardening off outdoors for a few hours a day, increasing gradually.
• Week 7 to 8 plus: transplant after your last frost date when nights stay above 50°F.

For the equipment and technique side, including trays, mix, lights and watering, see our full guide on how to start seeds indoors. When it is time to move seedlings outside, our guide on hardening off seedlings lays out a day-by-day schedule.

Can You Direct Sow Tomatoes Instead?

You can, but only where the season is long enough. Direct-sown tomatoes need warm soil (at least 60°F, better 70°F) to germinate, so they go in around or after your transplant date and fruit several weeks later than transplants. That can work for cherry tomatoes in zones 8 and warmer, but in most of the country starting indoors gives you a significantly longer harvest. Tomatoes that sprout on their own from last year’s fallen fruit show that it is possible; they just ripen late.

Growing Tomatoes Indoors Year-Round

If you want to grow tomatoes entirely indoors rather than starting transplants for the garden, timing works differently because you control the light and temperature. Compact cherry and dwarf varieties are best. Our guide on growing tomatoes indoors covers that setup. For planning the rest of your spring garden, see our vegetable gardening hub.