Why Your Seeds Are Not Germinating in Hot Weather
Above 85°F, some seeds go dormant or die. Lettuce and spinach are most sensitive.
Temperature Thresholds (Upper Limits)
| Soil Temp | Effect |
|---|---|
| 85°F | Some seeds go dormant |
| 90°F | Lettuce, spinach stop germinating |
| 95°F | Most cool-season crops fail |
| 100°F+ | Soil pathogens kill most seeds |
What to Do
Option 1: Shade the soil — Cover with shade cloth. Option 2: Water more often — Hot soil dries fast. Option 3: Plant in the evening — Soil is cooler. Option 4: Start indoors — Germinate inside at 65-75°F. Option 5: Wait for fall.
Heat-Sensitive Varieties
| Variety | Max Germination Temp |
|---|---|
| Lettuce | 80°F |
| Spinach | 75°F |
| Cilantro | 80°F |
| Peas | 80°F |
| Broccoli | 85°F |
Common Questions
Can I refrigerate seeds to break dormancy? Not helpful for heat dormancy.
Will lettuce seeds germinate in summer? Sometimes, with shade and constant moisture.
Should I water seeds with cold water? No. Use room-temperature water.
Can I plant in partial shade in summer? Yes. Morning sun + afternoon shade.
How do I know if seeds are dead vs dormant? Paper towel test at 70°F.
Is it better to start indoors in summer? Yes, for cool-season crops.