One trick to successful gardening in Texas, especially vegetable crops, is knowing when to plant. Checking the signs of the moon and trying to predict the last frost in Texas is a fun mental challenge, but it might not be very predictable.
Soil temperature is the most important factor to consider for good seed germination and seedling growth. Soil temperature for vegetable seed growth is classified into four categories: the minimum temperature for seed growth; the optimum temperature; a realistic temperature; and the maximum temperature for germination to occur.
The minimum soil temperature is the lowest temperature the soil can be for seed germination. Some cold season crops like beets, cabbage, chard, radish, and turnip have a minimum soil temperature of 40 degrees F. If we plant at the minimum soil temperature, we might have slow germination and weak seedlings. The maximum soil temperature is the highest temperature at which the seeds will germinate. Seeds planted at the maximum soil temperature or higher will not be likely to germinate.
The optimum soil temperature is the best temperature for seed germination. The optimum temperature for seed germination of cucumber, okra, and watermelon is 95 degrees F. At this temperature, we will get the best germination. Unfortunately, if we plant those seeds when the soil temperature is 95 degrees F, the summer heat will stress the plant and reduce plant vigor and yield.
Gardeners want to hit the sweet spot of the realistic soil temperature. This is somewhere between the minimum and optimum temperature so the seeds will germinate and have the best chance for growth. For example, the optimum soil temperature for seed germination of lettuce is 75 degrees F, and the minimum soil temperature is 35 degrees F. The realistic soil temperature to plant lettuce is 45 degrees F so the lettuce has a good chance to germinate and the plant will have plenty of time to grow before the weather gets too warm.
If you are getting ready to plant a spring garden, be sure to buy a soil thermometer and look up the soil temperature recommendations at https://aggie-horticulture.tamu.edu/vegetable/easy-gardening-series/.
For more information about gardening, contact the Williamson County AgriLife Extension Office at 512-943-3300.
