When to Start Seeds Indoors: Complete Guide by Plant & Zone (2026)
Exact seed-starting dates for 70+ vegetables, herbs, and flowers — calculated from your last frost date, grouped by plant family, and broken down by USDA zone.
By MyLocalPlanting Editorial Team · Updated 2026 · Sources
The most common seed-starting mistake isn't using bad soil or cheap lights — it's starting at the wrong time. Start too early and you'll have leggy, root-bound seedlings that shock when they finally hit the garden. Start too late and you've lost weeks of growing season you'll never get back.
Every plant on this list has a specific window, measured in weeks before your last frost date. A tomato needs 6 weeks. A pepper needs 10. A zucchini only needs 3 — and starting it any sooner is actively counterproductive. This guide gives you the exact numbers for 73+ plants, explains why each window exists, and shows you how to calculate your personal seed-starting calendar from your ZIP code.
Find your exact seed-starting dates
Enter your ZIP code to get a personalized planting calendar with exact dates for every plant below.
The Formula: Last Frost Date Minus X Weeks
Every seed-starting date follows the same formula: find your average last spring frost date, then count backward the number of weeks that plant needs indoors.
Seed-Start Date = Last Frost Date − Weeks Needed Indoors
Example: Last frost April 15 − 6 weeks = Start tomatoes indoors March 4
Your last frost date comes from NOAA climate normals — the 30-year average for your area. It's not a guarantee (late frosts happen), but it's the standard baseline used by cooperative extensions and the USDA. To find yours precisely, enter your ZIP code in the tool above.
One important nuance: the "weeks before last frost" number accounts for both the time indoors and the hardening-off period. Most transplanting guides assume 1–2 weeks of hardening off before the final move outdoors — so a plant listed at "6 weeks" might spend 4–5 weeks under grow lights and 1–2 weeks transitioning outdoors.
Seed-Start Dates by Zone: Tomatoes & Peppers
Tomatoes = 6 weeks before last frost · Peppers = 10 weeks before last frost
| Zone | Last Frost | Start Tomatoes | Start Peppers |
|---|---|---|---|
| 3a–3b | May 20–25 | Apr 6–11 | Feb 18–25 |
| 4a–4b | May 10–15 | Mar 29 – Apr 3 | Feb 13–18 |
| 5a–5b | May 5–10 | Mar 24–29 | Feb 9–13 |
| 6a–6b | Apr 20–25 | Mar 9–14 | Jan 26 – Feb 1 |
| 7a–7b | Apr 5–10 | Feb 22 – Mar 1 | Jan 11–18 |
| 8a–8b | Mar 15–25 | Feb 3–13 | Dec 23 – Jan 3 |
| 9a–9b | Feb 15–25 | Jan 6–15 | Nov 12–23 |
Based on NOAA average last frost dates by USDA zone. Zone 9–10 pepper start dates fall in the prior calendar year.
Seed-Starting Schedule: 73+ Plants by Timing Group
Organized from slowest to fastest. All timings are relative to your average last spring frost date.
| Plant | Category | Days to Harvest | Plant Guide |
|---|---|---|---|
| Brussels Sprout | vegetable | 84 days | View guide → |
| Habanero Pepper | vegetable | 100 days | View guide → |
| Plant | Category | Days to Harvest | Plant Guide |
|---|---|---|---|
| Lavender | herb | 90 days | View guide → |
| Rosemary | herb | 120 days | View guide → |
| Bell Pepper | vegetable | 70 days | View guide → |
| Cayenne Pepper | vegetable | 75 days | View guide → |
| Celery | vegetable | 130 days | View guide → |
| Chili Pepper | vegetable | 119 days | View guide → |
| Jalapeño Pepper | vegetable | 75 days | View guide → |
| Leek | vegetable | 120 days | View guide → |
| Poblano Pepper | vegetable | 80 days | View guide → |
| Serrano Pepper | vegetable | 80 days | View guide → |
| Echinacea (Coneflower) | flower | 365 days | View guide → |
| Petunia | flower | 75 days | View guide → |
| Lemongrass | herb | 100 days | View guide → |
| Ginger | herb | 270 days | View guide → |
| Stevia | herb | 90 days | View guide → |
| Shishito Pepper | vegetable | 60 days | View guide → |
| Banana Pepper | vegetable | 70 days | View guide → |
| Impatiens | flower | 60 days | View guide → |
| Salvia (Annual) | flower | 75 days | View guide → |
| Plant | Category | Days to Harvest | Plant Guide |
|---|---|---|---|
| Basil | herb | 60 days | View guide → |
| Chives | herb | 60 days | View guide → |
| Marjoram | herb | 60 days | View guide → |
| Oregano | herb | 80 days | View guide → |
| Parsley | herb | 75 days | View guide → |
| Sage | herb | 75 days | View guide → |
| Tarragon | herb | 60 days | View guide → |
| Thyme | herb | 90 days | View guide → |
| Artichoke | vegetable | 150 days | View guide → |
| Asparagus | vegetable | 730 days | View guide → |
| Eggplant | vegetable | 70 days | View guide → |
| Okra | vegetable | 91 days | View guide → |
| Onion | vegetable | 100 days | View guide → |
| Rhubarb | vegetable | 365 days | View guide → |
| Shallot | vegetable | 90 days | View guide → |
| Catnip | herb | 90 days | View guide → |
| Valerian | herb | 365 days | View guide → |
| Bee Balm | herb | 365 days | View guide → |
| Lovage | herb | 365 days | View guide → |
| Snapdragon | flower | 60 days | View guide → |
| Pansy | flower | 50 days | View guide → |
| Columbine | flower | 365 days | View guide → |
| Verbena | flower | 85 days | View guide → |
| Plant | Category | Days to Harvest | Plant Guide |
|---|---|---|---|
| Chamomile | herb | 60 days | View guide → |
| Lemon Balm | herb | 70 days | View guide → |
| Beefsteak Tomato | vegetable | 85 days | View guide → |
| Broccoli | vegetable | 60 days | View guide → |
| Cabbage | vegetable | 70 days | View guide → |
| Cauliflower | vegetable | 75 days | View guide → |
| Cherry Tomato | vegetable | 60 days | View guide → |
| Collard Green | vegetable | 60 days | View guide → |
| Grape Tomato | vegetable | 65 days | View guide → |
| Heirloom Tomato | vegetable | 80 days | View guide → |
| Roma Tomato | vegetable | 75 days | View guide → |
| Tomato | vegetable | 70 days | View guide → |
| Marigold | flower | 50 days | View guide → |
| Tomatillo | vegetable | 75 days | View guide → |
| Napa Cabbage | vegetable | 70 days | View guide → |
| Lemon Verbena | herb | 120 days | View guide → |
| Dahlia | flower | 90 days | View guide → |
| Hollyhock | flower | 365 days | View guide → |
| Celosia | flower | 75 days | View guide → |
| Plant | Category | Days to Harvest | Plant Guide |
|---|---|---|---|
| Acorn Squash | vegetable | 85 days | View guide → |
| Butternut Squash | vegetable | 100 days | View guide → |
| Cantaloupe | vegetable | 80 days | View guide → |
| Fennel | vegetable | 80 days | View guide → |
| Honeydew Melon | vegetable | 85 days | View guide → |
| Kohlrabi | vegetable | 55 days | View guide → |
| Radicchio | vegetable | 80 days | View guide → |
| Spaghetti Squash | vegetable | 90 days | View guide → |
| Watermelon | vegetable | 80 days | View guide → |
| Zucchini | vegetable | 50 days | View guide → |
Plants That Should NOT Be Started Indoors
Not every vegetable benefits from indoor starting. These crops do better — or only work — when direct-seeded outdoors. Starting them indoors wastes time and often produces inferior results.
Long taproot snaps during transplanting; direct sow 2–4 weeks before last frost
Mature in 25–30 days; direct sow is faster than any indoor head start
Bolt from root disturbance; direct sow 4–6 weeks before last frost
Cold-tolerant; direct sow 4–6 weeks before last frost while soil is still cool
Fast-germinating; direct sow after last frost for best results
Needs wind pollination in blocks; spacing makes indoor starting impractical
Prefers cool soil; direct sow 6–8 weeks before last frost or in fall
Surface-sows easily; can be direct-seeded in early spring or succession-planted
What You Need to Start Seeds Indoors
You don't need a lot of equipment, but a few things genuinely matter. Skip grow lights and you'll get leggy seedlings. Skip a heat mat for peppers and germination will be slow and uneven.
The single most important purchase. Seedlings need 14–16 hours of bright light. A south window rarely delivers enough. LED shop lights or dedicated grow lights work equally well — keep them 2–3 inches above seedlings.
Sterile, finely textured, fast-draining. Regular potting soil is too heavy and holds too much moisture, promoting damping-off fungus. Don't use garden soil indoors.
Important for peppers and eggplant, which germinate best at 80–85°F. Optional for tomatoes and most other crops. Set it to 75–80°F and remove once seedlings emerge.
72-cell or 50-cell trays are standard for starting seeds. Upgrade to 4-inch pots once seedlings have their first true leaves and before roots circle the bottom.
Speeds germination by trapping moisture. Remove it as soon as seedlings emerge — high humidity after emergence promotes fungal disease.
Plug grow lights into a timer set for 16 hours on / 8 hours off. Consistent light cycles matter more than total wattage.
Seed-Starting Tips by Zone
Your USDA hardiness zone determines your last frost date, which drives your entire seed-starting calendar. Here's how the timing plays out across the country.
Zones 3–4 (Northern Minnesota, Maine, Montana)
Last frost: May 15 – June 1Short growing seasons mean indoor starting is essential for most warm-season crops. Start peppers and eggplant in late January, tomatoes in late March. Cold frames and row cover extend both ends of the season. Some crops (squash, beans) may still benefit from a 2–3 week head start even though they're typically direct-sown farther south.
See tomato dates for Minnesota →Zones 5–6 (Midwest, Mid-Atlantic, Pacific Northwest)
Last frost: April 20 – May 15The most common zone range for US gardeners. Start peppers in late January or early February, tomatoes in mid-March. This is the zone where the 6-week tomato rule originates — it's the sweet spot between getting a head start and avoiding overgrown seedlings.
See tomato dates for Ohio →Zones 7–8 (Mid-South, Pacific Coast, Pacific Northwest)
Last frost: March 15 – April 10Warmer zones allow earlier outdoor planting but also earlier indoor starting. Peppers often need to start in November or December for the prior season's calendar year. The upside: longer seasons allow two rounds of warm-season crops or succession planting of cool-season greens after summer heat breaks.
See tomato dates for Virginia →Zones 9–10 (Gulf Coast, Southern California, Southwest Desert)
Last frost: January 15 – March 1Many gardeners in these zones skip indoor starting for warm-season crops and direct sow or buy transplants. The main use for indoor starting here is getting a jump on fall gardens — starting tomatoes indoors in July for a September transplant. Peppers and eggplant can be grown as perennials in frost-free microclimates.
See tomato dates for Texas →5 Seed-Starting Mistakes (and How to Fix Them)
Starting Too Early
Fix: Use the weeks-before-last-frost formula, not a calendar date. If your last frost is May 10 and tomatoes need 6 weeks, that's March 29 — not "sometime in February" because it felt right.
Using Window Light Instead of Grow Lights
Fix: Windows give seedlings maybe 4–6 hours of usable light on a sunny day. Grow lights give 16 hours. Leggy seedlings with thin stems are almost always a light problem, not a watering or soil problem.
Using Garden Soil or Heavy Potting Mix
Fix: Buy a bag of dedicated seed-starting mix. It costs $8–12 and prevents damping-off (the fungal disease that collapses seedlings at the soil line). Reuse it in raised beds afterward.
Skipping Hardening Off
Fix: Set seedlings outside in a sheltered, partly shaded spot for 1–2 hours the first day. Add an hour and more direct sun each day for 7–14 days. Never go from a grow tent to full afternoon sun in one step.
Overwatering Seedlings
Fix: Water when the top ½ inch of mix is dry, not on a schedule. Bottom-water by setting trays in a shallow dish of water and letting the mix absorb from below — this keeps the surface drier and reduces damping-off risk.
How to Start Seeds Indoors: Step by Step
- 1
Find your last frost date
Enter your ZIP code in the tool on this page, or check the NOAA frost date maps. Write the date down — everything else is calculated from it.
- 2
Build your seed-starting calendar
For each plant you want to grow, subtract the required weeks from your last frost date. That's your seed-start date. Write the calendar out or use a spreadsheet — overlapping start dates are common.
- 3
Fill trays with seed-starting mix
Moisten the mix before filling trays (easier than watering afterward). Fill cells to the top, tamp lightly. Pre-moistened mix should clump when squeezed but not drip.
- 4
Sow seeds at the right depth
Most seeds go in at 2–3× their diameter. Tiny seeds (basil, celery) get pressed onto the surface and barely covered. Check the seed packet — many crops have specific depth requirements.
- 5
Cover and provide bottom heat
Cover trays with a humidity dome until germination. Use a heat mat for peppers and eggplant (they germinate best at 80–85°F). Most other crops germinate fine at room temperature (65–70°F).
- 6
Move to grow lights immediately after germination
Remove the humidity dome and move seedlings to 2–3 inches below your grow lights as soon as the first sprout emerges. Don't wait for all cells to germinate — early sprouts will stretch fast without light.
- 7
Pot up before roots circle the bottom
When you see roots emerging from drainage holes or wrapping the outside of the root ball, move up to a 4-inch pot. Letting plants become root-bound stunts their growth permanently.
- 8
Harden off for 7–14 days before transplanting
Start with 1–2 hours of filtered outdoor light, increase daily. After a week, leave plants out overnight if temperatures stay above 50°F. Transplant on a cloudy day or in the evening to reduce stress.
Growing Guides for Top Indoor-Start Crops
Tomato
Start 6 weeks before frost
Bell Pepper
Start 10 weeks before frost
Eggplant
Start 8 weeks before frost
Broccoli
Start 6 weeks before frost
Cabbage
Start 6 weeks before frost
Basil
Start 8 weeks before frost
Celery
Start 10 weeks before frost
Leek
Start 10 weeks before frost
Zucchini
Start 4 weeks before frost
Frequently Asked Questions
How many weeks before the last frost should I start seeds indoors?
It depends on the plant. Peppers and Brussels sprouts need 10–12 weeks. Tomatoes, eggplant, and most herbs need 6–8 weeks. Fast-growers like squash and melons only need 2–4 weeks. Starting too early produces overgrown, root-bound seedlings that struggle after transplanting.
What happens if I start seeds indoors too early?
Seedlings outgrow their containers and become root-bound, leggy, and stressed before outdoor conditions are safe for transplanting. They also compete for light and airspace, which increases disease risk. A seedling that's been waiting 3 weeks too long in a 4-inch pot will often underperform one started at the right time.
Can I start seeds indoors without a grow light?
A south-facing window can work for slow, low-light plants like lettuce or herbs, but most vegetable seedlings need 14–16 hours of bright light per day. Window light is rarely sufficient — seedlings stretch toward it and become "leggy" (tall, weak stems). A basic 2-bulb shop light with T8 fluorescent or LED grow bulbs positioned 2–3 inches above seedlings solves this for under $40.
What soil should I use for starting seeds indoors?
Use a dedicated seed-starting mix, not regular potting soil or garden soil. Seed-starting mix is finely textured, sterile, and drains quickly — preventing the damping-off fungus that kills seedlings at the soil line. Once seedlings have their first true leaves and you're moving them to larger containers, switch to a quality potting mix.
What is hardening off and why does it matter?
Hardening off is the 7–14 day process of gradually exposing indoor seedlings to outdoor conditions (wind, direct sun, temperature swings) before transplanting. Skipping it causes transplant shock — wilting, sunscald, or stunted growth. Start with 1–2 hours of filtered shade outdoors, then increase daily sun exposure and time over 1–2 weeks.
Do all vegetables need to be started indoors?
No — many vegetables actually do better direct-seeded outdoors. Carrots, radishes, beets, peas, beans, corn, and most salad greens prefer to be sown where they'll grow and don't transplant well. The crops that benefit from indoor starting are mainly those with long growing seasons (peppers, tomatoes, eggplant) or slow germination (celery, leeks).
How do I know my last frost date?
Your last frost date is based on NOAA climate normals for your area — it's the date after which there's historically a 50% chance of frost. Enter your ZIP code in the tool on this page for your exact date, or look up your USDA hardiness zone. Zones 5–6 typically see last frost in late April to mid-May; zones 7–8 in late March to early April.
Get Your Personalized Seed-Starting Calendar
Enter your ZIP code for exact seed-start dates calculated from your local last frost date — for every plant in your garden.
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