Indoor Seed Starting Calendar
Find out exactly when to start each vegetable seed indoors based on your USDA hardiness zone. Get personalized start dates, transplant dates, and harvest timelines.
Starting seeds indoors gives warm-season crops like tomatoes, peppers, and eggplant the head start they need to produce a full harvest. The key is timing: start too early and seedlings get leggy, start too late and you lose weeks of growing season. Select your zone below to see a complete seed starting schedule.
Data last updated: March 2026
Not sure? Check the planting dates calculator to look up your zone by ZIP code.
Seed Starting Essentials
LED Grow Lights
Full-spectrum grow lights give seedlings the light intensity they need to grow strong and stocky instead of leggy.
Seed Starting Trays
Cell trays with humidity domes keep soil moist during germination. Look for trays with drainage holes and sturdy construction.
Seedling Heat Mats
Heat mats warm soil 10 to 20 degrees above room temperature, speeding up germination for peppers, tomatoes, and eggplant.
Get Planting Reminders
We'll email you when it's time to start seeds, transplant, and harvest based on your zone. No spam, just seasonal alerts.
Frequently Asked Questions
It varies by crop. Peppers, eggplant, onions, and leeks need the longest lead time at 10 weeks before last frost. Tomatoes, broccoli, cabbage, and parsley need 8 weeks. Lettuce, spinach, kale, and basil need about 6 weeks. Quick growers like cucumbers, zucchini, and watermelon only need 3 to 4 weeks. Starting too early leads to leggy, root-bound transplants, so follow the timing for each vegetable.
How This Calendar Works
This seed starting calendar calculates your indoor start dates by counting backwards from your zone's average last frost date. Each vegetable has a recommended number of weeks to grow indoors before transplanting outside. For example, tomatoes and peppers need 8 to 10 weeks indoors, while cucumbers and squash only need 3 to 4 weeks. The calendar also shows your transplant date and estimated days to harvest after transplanting so you can plan your full growing season.
Tips for Starting Seeds Indoors
- Use a sterile seed starting mix, not garden soil. Garden soil can harbor disease pathogens and compacts too easily in small cells.
- Provide 14 to 16 hours of light per day with a grow light positioned 2 to 4 inches above seedlings. A sunny window alone is usually not enough and leads to leggy, weak plants.
- Bottom water by setting trays in a shallow dish of water for 10 to 15 minutes. This encourages roots to grow downward and reduces the risk of damping off disease.
- Harden off seedlings for 7 to 10 days before transplanting. Start with 1 hour of outdoor shade, gradually increasing sun exposure and time each day.
- Once you know your transplant dates, use the seed spacing calculator to plan how many transplants you need for your garden beds.
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