When installed, minimal additional soil was added on the existing ground before placing our celebration bermuda sod. The natural ground in our area of Texas (Leander, North of Austin) consists of minimal soil with fractured limestone.

Rather than just keep the lawn green as is, I would like to increase it's capacity for moisture and improve the soil. Beyond regular feedings of milorganite and alfalfa pellets (which the deer love) and occasional shampoos, I plan to semiannually add about 1/4" of a top dress mix from a local nursery (which consists of loam, sand, screened compost, and granite fines). I plan to follow this regimen for several years until I've increased overall soil depth on the lawn by about 1".

For this locality, would a top dressing in September be appropriate? I think we still have a couple months of growing left before the grass goes dormant. Also, is there a problem with spreading milorganite PRIOR to top dressing?

Thanks for any advice!
Will