An effective fertilizer for St. Augustine grass is two to four pounds of nitrogen per 1,000 feet of lawn a year, according to Clemson University's Cooperative Extension. The fertilizer should first be applied in the spring, after the last frost. A nitrogen-phosphorus-potassium fertilizer with a 4-1-2 ratio is sufficient.
To fine-tune the fertilizer needs of the lawn, the soil should be tested. It may need amendments such as lime or other nutrients.
Nitrogen fertilizers can be quick- or slow-release, according to SFGate. Lawns respond to quick-release fertilizers in as little as a week, while it can take 10 weeks to see results with a slow-release fertilizer. It doesn't matter if the fertilizer is organic or inorganic.