When to divide? “This is the perfect time to divide daylilies in our zone. I live just 40 miles west of Houston and we always wait until the hot days and cool nights have passed. Now that the temps are in the range from 75-85 this means the weather is perfect. You can also pot up daylilies that you have divided. I use 3-gallon pots for either new purchases or one that I want to keep for the Spring sales. You can divide daylilies up until December in our lower part of the state.” Forum response from here.