St. Augustine grass (Stenotaphrum secundatum) is a warm-season turf variety used across the Southern United States for its dense, carpet-like growth and blue-green color. It thrives in warm, humid climates and exhibits good shade and salt tolerance, making it a common choice in coastal regions and under trees. This guide details the specific preparation and care required to establish this resilient grass from seed.
Understanding the Viability of St. Augustine Seed
St. Augustine grass is traditionally established using sod or plugs because most cultivars do not produce commercially viable seed. Most St. Augustine cultivars are propagated vegetatively, meaning they are grown from pieces of the plant itself, not from seed. Viable seed is rare, often expensive, and typically only available for proprietary cultivars bred to produce fertile seed.
If viable seed is acquired, planting timing is crucial. The seed requires consistently high soil temperatures for successful germination, ideally between 70°F and 80°F. This period generally occurs in late spring to early summer, between May and August, after the last threat of frost has passed. Growing St. Augustine from seed is a high-risk method compared to using sod or plugs, which offer instant coverage and a higher rate of establishment.
Preparing the Planting Site
Thorough site preparation is the most important factor for success when planting St. Augustine seed. Begin by completely clearing the area of any existing vegetation, including old turf, weeds, and debris, to eliminate competition for the young seedlings. Applying a non-selective herbicide two weeks before planting can help ensure a clean slate, but any remaining residue should be removed before sowing.
Perform a professional soil test to determine the exact pH and nutrient levels. St. Augustine grass performs best in a slightly acidic to neutral pH range, ideally between 6.0 and 7.5. If the soil test reveals the pH is outside this optimal range, amendments like lime (to raise pH) or sulfur (to lower pH) should be incorporated into the soil.
The soil needs to be loosened to a depth of 4 to 6 inches to promote healthy root development. Tilling allows for the incorporation of organic matter, such as compost or peat moss, which improves drainage and water retention. Apply a starter fertilizer that is low in nitrogen but high in phosphorus to encourage strong root growth. Lightly rake the fertilizer into the top inch of soil, then lightly roll or level the surface to create a smooth, firm seedbed.
Sowing the Seed and Initial Application
Sowing the seed must be done evenly to ensure uniform density in the final lawn. The recommended application rate is typically between 1/3 and 1/2 pound per 1,000 square feet. Using a drop spreader is the most effective method for achieving precise and consistent coverage.
To ensure uniform distribution, divide the total seed amount into two equal halves. Apply the first half by walking the spreader in one direction, then apply the second half perpendicular to the first pass, a technique known as cross-hatching. Lightly incorporate the seed into the soil to ensure good seed-to-soil contact. This is done by lightly raking the area or rolling it, ensuring the seed is covered by no more than 1/8 inch of soil.
Apply a thin layer of straw or peat moss over the seeded area to help retain moisture and protect the seed from wind or heavy rain. The mulch should be thin enough so the soil is still partially visible, allowing sunlight to reach the seeds. This initial cover helps moderate soil temperature fluctuations, supporting the sensitive germination process.
Nurturing the Seedlings for Establishment
The care of new seedlings is the most delicate stage, as improper watering is the most common cause of failure. During the germination phase, which can take between 14 and 21 days, the top inch of soil must be kept constantly moist, but never saturated. This usually requires light, frequent watering sessions, perhaps three to four times daily, depending on the heat and sun exposure. Once the seeds have successfully germinated, you can begin to reduce the frequency of watering while increasing the duration, a process that encourages the roots to grow deeper into the soil.
After the first week or two, transition to watering once or twice per day, applying a slightly larger amount of water each time. By the third or fourth week, the new grass should be established enough to reduce watering to a deeper application every two or three days. The first mowing should occur when the grass blades reach a height of 3 to 4 inches.
Set the mower deck to the highest setting, never removing more than one-third of the total blade height in a single pass to prevent shocking the young plants. The bare soil between the new seedlings is highly susceptible to weed growth, which will compete with the grass for water and nutrients. Pre-emergent herbicides, which prevent weed seeds from sprouting, should be avoided until the St. Augustine lawn is fully established, typically six to eight weeks after germination. Any weeds that appear before this time should be carefully removed by hand to minimize soil disturbance and protect the delicate new grass roots.