Early Spring Seed Starting: Cold Frames, Germination Timing, and Sun Exposure

Cold Frame vs. Indoor Starting

Use cold frames only for cold-hardy crops: lettuce, spinach, onions, cabbage, peas, cauliflower. Tender crops (peppers, tomatoes, basil) must start indoors under lights.

Germination Temperature Reality

• Ideal: 65–70°F (18–21°C).
• Cooler temps = slower germination. Rule of thumb: double time per 10°F below 65°F.
• Peppers/tomatoes in 50°F soil may take 3–4 weeks vs. 7–10 days at 75°F.

Critical: Hardening Off Before Sun Exposure

Never move seedlings directly from indoor/low-light to full sun. The 7-day hardening off process (shade → increasing sun) prevents fatal sun scald. Your covered pots in the shed lacked both light and proper temperature control.

Best Practice for Next Season

1. Start tender crops indoors under grow lights 6–8 weeks before last frost.
2. Use heat mats for peppers/eggplants (80°F soil).
3. Transplant to cold frame only after hardening off.
4. Direct-sow only cold-hardy seeds outdoors.