St. Augustine is a warm season, semi-tropical lawn grass commonly planted as an ornamental lawn, but rarely for activity-heavy turf grass. While St. Augustine is considered to be fairly drought tolerant, it requires regular irrigation to remain green and lush according to Texas A&M University Extension. Extended periods of drought will stress the lawn and kill off the top foliage in patches. Reducing stress on the grass during periods of drought is key to its survival and rehabilitation.
Irrigate the lawn deeply once to three times per week, applying at least 1 inch of water per week. Water enough to keep the soil moist to the touch just under the thatch. Water in the early morning hours to reduce moisture loss to evaporation and bolster the lawn during the hottest part of the day.
Raise the mowing height on your St. Augustine lawn grass to slow its growth and the respiration rate of the lawn grass. Increasing the mowing height by 1/2 inch or more from normal height, will reduce the plants' need to create new blade growth as quickly, thereby conserving moisture and soil nutrients. Keep your St. Augustine grass between 2 and 3 inches in blade length during drought conditions.
Refrain from applying nitrogen fertilizers during periods of drought. Fertilizers drive the plants to produce new top growth, stressing the plants, exacerbating drought stress and depleting precious moisture and nutrients in the soil. Resume a regular fertilizing regimen when the lawn has recovered, temperatures have cooled a bit, and water is plentiful.