April 15th marks the average last frost date for most of Oklahoma. It’s important to note, though, that this is an average. Freezes may end as early as March or sneak up on gardeners in early May. Warm season vegetables can be planted once the freeze threat has passed.

This is true for tomatoes, one of the most beloved garden vegetables. Even though tomatoes are a warm season crop, they are not particularly heat tolerant. Tomatoes are native to the high elevations of the Andes Mountains and prefer warm, mild days and cool nights. Specifically, plants perform best with daytime temperatures between 70° and 76°F and nighttime temperatures around 68°F. These conditions only exist in Oklahoma for a short period before transitioning into a much hotter environment.

The cool nighttime temperatures are critical for fruit set. When exposed to higher than optimum temperatures, pollen development accelerates and viability is reduced before fertilization can occur. Flower structure can also be distorted by high temperatures, making it difficult for pollen to be properly transferred within the flower.