Guide
Starting seeds indoors gives warm-season crops a head start so they mature and produce before fall frost arrives. But timing is everything: start too early and your seedlings become leggy and pot-bound before it's safe to plant out; start too late and you lose the head start entirely. The trick is to count backward from your last spring frost date.
Every crop has a recommended number of weeks it should spend indoors before transplanting. To find your indoor sowing date, take your last frost date and subtract that number of weeks. If your last frost is May 15 and tomatoes need six weeks indoors, you'd sow seeds around April 3. The frost date planner does this math automatically for 50+ vegetables, herbs, and flowers once you enter your zip code.
| Crop | Weeks indoors before last frost |
|---|---|
| Peppers, eggplant | 8–10 weeks |
| Tomatoes | 6–8 weeks |
| Broccoli, cabbage, kale | 4–6 weeks |
| Basil | 4–6 weeks |
| Cucumbers, squash, melons | 2–4 weeks |
Fast-growing vine crops like cucumbers and squash resent root disturbance, so they only need a couple of weeks indoors — or can be direct-sown after frost. Slow starters like peppers and eggplant benefit from the longest indoor lead time.
Root crops such as carrots, beets, radishes, and turnips are direct-sown because transplanting disturbs the developing root. Beans, peas, and corn also germinate quickly outdoors and rarely benefit from an indoor start. Knowing which crops to sow directly saves you tray space for the plants that truly need the head start.
Indoors, seedlings need bright light for 14–16 hours a day — a sunny windowsill is rarely enough, so most gardeners use a full-spectrum grow light positioned a few inches above the plants. Warm soil (around 70°F) speeds germination for warm-season crops. Once true leaves appear, a gentle breeze from a fan helps produce sturdy, stocky stems.
Seedlings raised indoors have never felt direct sun, wind, or temperature swings. Moving them straight outside can shock or kill them. Instead, harden off over 7–14 days: start with one to two hours in a sheltered spot, then gradually increase outdoor time and exposure each day. Only after this transition — and after your frost risk has passed — should tender crops go into the ground.
Enter your zip code in the frost date planner to get exact indoor-sowing and transplant dates for every crop in your garden.