Tomatoes should be planted when there is no danger of frost or cold weather. Generally, tomatoes can be planted outdoors around May unless the climate is particularly cold. Seeds started indoors can be started before the last frost around February.
Tomatoes do not grow when the temperature is too cold. Before planting tomatoes, it is best to check the soil to determine whether it is warm enough. The easiest way to check soil temperature is with a soil thermometer. If the soil temperature is 55 F or higher, tomatoes can be planted. Tomatoes planted in soil that is lower than 55 F could experience issues such as poor growth or seed rot.