Quick Scoop: Start indoor seeds based on your last frost date and the specific crop. A good rule is 6–8 weeks before last frost for many tomatoes, while peppers, onions, and slow growers often need 10–12 weeks , and fast growers like zucchini usually need only 3–4 weeks before the last frost.

Best timing

  • Tomatoes: 6–8 weeks before last spring frost.
  • Peppers, onions, leeks, some cool-season crops: often 10–12 weeks before frost, depending on variety.
  • Zucchini and other quick growers: about 3–4 weeks before frost.
  • Many vegetables and annual flowers: early to mid-March is a common starting window in some regions, but the exact timing still depends on your frost date and crop.

Simple rule

Use this formula:

  1. Find your average last frost date.
  2. Check the seed packet for the recommended indoor-start window.
  3. Count backward from that frost date by the listed number of weeks.

Practical tip

If you start too early, seedlings can become leggy and overgrown before transplant time, so it’s usually better to start a little later than too soon. For best results, seedlings also need good light, proper moisture, and warm germination conditions.

If you want, I can help you figure out the exact indoor planting date for your specific crops using your local last frost date.