We recorded 56-58°F temperatures from soils in various Central Jersey commercial vegetable fields on April 15 –Tax Day– just before the recent multi-day cold front rolled in. The good news is 56-58°F was higher than I anticipated.
What do soil temperatures have to do with your early vegetable seedlings?
- Mean spring soil temperatures determine early root growth and crop development.
- By tracking spring soil temperatures from your fields you’ll become a more profitable farmer.
- Matching your earlier warming fields to tolerant seedlings of vegetables found in the table below is worthwhile.
When it is sunny or when the wind is howling, judging the suitability for planting is clear. However, field specific soil temperature differences are also critical for various seedlings. Farmers have well known “hot fields,” that over many seasons have proven reliability for early planting. Likewise, most sweet corn seed companies provide relative ratings as to how well particular varieties tolerate emergence in colder soils. It pays to track your field soil temperatures. Ideally, a soil thermometer should be used but even a metal food thermometer is acceptable.
While it’s best to measure soil temperatures in your own fields, there are online soil temperatures alternatives like The Rutgers NJ Weather & Climate Network. Twelve of the weather stations offer real time soil temperatures. Check the numbered station nearest your fields, and bookmark the station. Syngenta GreenCast offers broad regional soil temperature maps, with a 5-day soil prediction forecast feature. This is useful data when weather conditions are less than favorable and only narrow planting windows exist.
These temperatures represent vegetable seedling survival tolerance, not necessarily best performance:
| Average Minimum Spring Soil Temperatures | Vegetable Seedlings Tolerating Minimum |
| 40°F | Beet, Cabbage, Potato, Spinach, Turnip |
| 45°F | Pea, Mustard, Leek |
| 50°F | Carrot, Lettuce, Onion, Sweet Corn |
| 60°F and above | Bean, Cucumber, Pumpkin, Squash |
| 70°F and above | Eggplant, Watermelon |
