Seed Starting Calendar
Find out exactly when to start seeds indoors, transplant outside, and expect your harvest based on your state and plant type.
Select your state and plant type to see your seed starting calendar.
About Seed Starting
Starting seeds indoors gives your plants a head start on the growing season, especially in northern states with short summers. By the time it is warm enough to plant outside, your seedlings will already be several weeks old and ready to take off. This is particularly important for warm-season crops like tomatoes and peppers that need a long growing season to produce fruit.
Seed Starting Lead Times
| Plant | Start Indoors | Direct Sow? | Days to Harvest |
|---|---|---|---|
| Tomatoes | 6-8 weeks before last frost | No | ~75 days |
| Peppers | 8-10 weeks before last frost | No | ~80 days |
| Herbs | 4-6 weeks before last frost | Yes | ~60 days |
| Lettuce | Direct sow | Yes (2 wk before frost) | ~50 days |
| Squash | Direct sow | Yes (2 wk after frost) | ~65 days |
| Flowers | 6-8 weeks before last frost | No | ~70 days |
Hardening Off Seedlings
Before transplanting indoor seedlings outside, they need a gradual transition called "hardening off." Start 7-10 days before your planned transplant date. Place seedlings outside in a sheltered, shady spot for 2-3 hours, then bring them back in. Each day, increase the time and sun exposure. By the end of the week, leave them out overnight if temperatures are above 50 F. This process strengthens cell walls and reduces transplant shock.
Indoor Growing Tips
Use a seed-starting mix (not garden soil) for best germination. Keep soil consistently moist but not waterlogged. Most seeds germinate best at 65-75 F soil temperature. Once seedlings emerge, they need 14-16 hours of bright light daily. A simple shop light with cool-white fluorescent or LED bulbs hung 2-3 inches above seedlings works well. Fertilize with a dilute liquid fertilizer once seedlings develop their first true leaves.
Frequently Asked Questions
When should I start seeds indoors?
It depends on the plant type and your last frost date. Tomatoes should be started 6-8 weeks before last frost, peppers 8-10 weeks, herbs 4-6 weeks, and flowers 6-8 weeks. Lettuce and squash are typically direct-sown outdoors rather than started inside. Use the calculator above to get exact dates for your state.
How do I harden off seedlings?
Start 7-10 days before transplanting. Place seedlings outside in a sheltered spot for 2-3 hours the first day, increasing time and sun exposure each day. Avoid windy or excessively hot days at first. By day 7-10, seedlings should be able to stay outside all day and overnight (if frost-free). This gradual process prevents transplant shock and sunburn on tender leaves.
Can I direct sow instead of starting indoors?
Some crops do better when direct-sown, including lettuce, squash, beans, peas, corn, and root vegetables like carrots and radishes. These plants either dislike root disturbance or grow quickly enough that a head start is not needed. However, tomatoes, peppers, and flowers benefit greatly from indoor starting, especially in zones with short growing seasons (Zones 3-5).
What grow lights do I need?
You do not need expensive grow lights for seed starting. Standard T8 or T5 fluorescent shop lights or LED strips work well. Position lights 2-4 inches above seedlings and run them 14-16 hours per day. Adjustable-height fixtures are ideal since you can raise the light as plants grow. Full-spectrum LEDs designed for plants provide slightly better results but are not required for starting seeds.