What ground temperature is best for planting tomatoes, beans, and marigolds?
Seeds of cool-season vegetables such as radish, lettuce, cabbage, carrot, etc., need at least a 45 degree F ground temperature to germinate. Tomatoes, beans, and marigolds need higher temperatures of more than 60 degrees F.
Tomato plants can be transplanted at 55 degrees F, but growth will be slow. Use a rule of thumb of a night air temperature minimum of 55 degrees F. By then, the days are a lot warmer and the soil is warmer than the coolest night air.
You can transplant tomatoes earlier by using wall-o'-waters. Fill the tubes with water. Place them over the planting site about a week prior to planting. Then remove the wall-o'-water and plant where it sat. After planting, replace the wall-o'-water over the plant until night temperatures reach 55 degrees F.
If you plant bean and marigold seeds when the soil is less than 60 degrees F, the seed will just sit. Some people wait until the temperature is 68 to 70 degrees F. Pepper and eggplant transplants should go in at this higher temperature.