This recommendation is specific to Texas and may or may not apply to your area.
The Mesquite tree blooming and a supposed final frost is not the signal to fertilize turf. The soil temperature must warm and the main grass type (e.g., St. Augustine, Bermuda) must begin to grow and be mowed twice before a slow-release fertilizer such as 19-5-9 should be applied. In San Antonio, that will not occur until May. If you fertilize too early, you will stimulate weed growth. When in doubt about timing of lawn maintenance activities, contact your local Cooperative Extension Service office for assistance.