Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu
Many vegetables are commonly direct seeded in the field. There are many factors that affect seed germination but soil temperature and moisture are the most critical. Other factors include seed quality (age, conditioning, handling), seed treatments, and seeding depth.
Early Spring Planted Crops
The table below shows the average days to germination for cold season crops. For example, peas will take over a month to geminate with soil temperatures at 41°F, two weeks with soil temperature of 50°F, and one week with soil temperature in the 70s. Spinach, onions, and radish will germinate at the lowest temperatures. Some crops (celery, lettuce, and spinach) stop germination at high soil temperatures.
| Average Days to Germination | ||||||||
| Crop | 32˚F | 41˚F | 50˚F | 59˚F | 68˚F | 77˚F | 86˚F | 95˚F |
| Beets | — | 42 | 17 | 10 | 6 | 5 | 5 | 5 |
| Cabbage | — | — | 15 | 9 | 6 | 5 | 4 | — |
| Collards | — | — | 15 | 9 | 6 | 5 | 4 | — |
| Carrots | none | 51 | 17 | 10 | 7 | 6 | 6 | 9 |
| Cauliflower | — | — | 20 | 10 | 6 | 5 | 5 | — |
| Celery | none | 41 | 16 | 12 | 7 | none | none | none |
| Kale | — | — | 15 | 9 | 6 | 5 | 4 | — |
| Lettuce | 49 | 15 | 7 | 4 | 3 | 3 | 3 | none |
| Onions | 136 | 31 | 13 | 7 | 5 | 4 | 4 | 13 |
| Parsley | — | — | 29 | 17 | 14 | 13 | 12 | — |
| Parsnips | 172 | 57 | 27 | 19 | 14 | 15 | 32 | none |
| Peas | — | 36 | 14 | 9 | 8 | 6 | 6 | — |
| Radishes | none | 29 | 11 | 6 | 4 | 4 | 3 | — |
| Spinach | 63 | 23 | 12 | 7 | 6 | 5 | 6 | none |
| Turnips | none | none | 5 | 3 | 2 | 1 | 1 | 1 |
Warm Season Crops
Most warm season crops will not germinate util soil temperature is above 50°F. Sweet corn will take over 3 weeks to germinate at 50°F but less than a week at 68°F. Snap beans will take over 2 weeks at 59°F but only one week at 77°F. Cucumbers are similar.
| Average Days to Germination | ||||||||
| Crop | 32˚F | 41˚F | 50˚F | 59˚F | 68˚F | 77˚F | 86˚F | 95˚F |
| Lima Beans | none | none | none | 31 | 18 | 7 | 7 | none |
| Snap Beans | none | none | none | 16 | 11 | 8 | 6 | 6 |
| Sweet Corn | none | none | 22 | 12 | 7 | 4 | 4 | 3 |
| Cucumbers | none | none | none | 13 | 6 | 4 | 3 | 3 |
| Eggplant | none | none | none | none | 13 | 8 | 5 | 5 |
| Melons | none | none | none | none | 8 | 4 | 3 | 3 |
| Okra | none | none | none | 27 | 17 | 13 | 7 | 6 |
| Peppers | none | none | none | 25 | 13 | 8 | 8 | 9 |
| Tomatoes | none | none | 43 | 14 | 8 | 6 | 6 | 9 |
| Watermelons | none | none | none | none | 12 | 5 | 4 | 3 |
This information came from UC Davis research over 60 years ago. Since that time, some crops have been bred for better cold germination such as sweet corn.
Spinach direct seeded on March 14 germinated in 10 days.