USTIN—They’re bright, blue and beloved. And they’re barely starting to show themselves in small patches along highways.

Blossoming bluebonnets signal spring is arriving and usher in Texans’ annual love affair with the famous wildflower.

Relatively dry weather the past few months should make for only an average Texas bluebonnet season, but moist conditions in the weeks to come could strengthen the display, said Andrea DeLong-Amaya, horticulture director at the Lady Bird Johnson Wildflower Center in Austin.

“The rain is good,” she said. “A lot of the bluebo...