St. Augustine is a beautiful, lush, frustratingly high-maintenance turfgrass. Between fertilizing, mowing, irrigating, and pest management, a healthy St. Augustine lawn can be a real labor of love.
Warm-season grasses like St. Augustine have similar maintenance requirements. However, this turf can be sensitive, so it’s important to implement a holistic care schedule to prevent pests, diseases, and thatch buildup.
Proper fertilizer choice and a timely application schedule is the key to a truly healthy St. Augustine turf. Balance a consistent fertilizer schedule with the proper mowing height, weed control, and irrigation schedule for a thick carpet of vigorous grass.
In a hurry? Download our FREE printable St. Augustine Fertilization And Maintenance Planner before you go!
What’s In A Fertilizer?
Fertilizers comprise a broad range of amendments that add some kind of nutritional benefit to the soil. Some are nutrient-specific, while others provide the full range of macro and micronutrients.
The most common fertilizers supply a balanced amount of nitrogen, phosphorus, and potassium. These amounts are represented on fertilizer bags by three numbers, like 12-12-12, 8-4-6, or 10-10-10. Multiply these percentages by the weight of the bag to determine the weight of each nutrient.
For example, a 10lb bag of 12-12-12 is 12% nitrogen, 12% phosphorous, and 12% potassium. The other 64% is fillers. To calculate the weight of each nutrient, multiply .12 by the total weight of the bag (10lbs.)
.12 x 10 = 1.2lbs each of nitrogen, phosphorus, and potassium.
Many cities have passed laws to limit the amount of nitrogen per application to 1lb per 1,000sq’. Nitrogen leaches through the soil easily, which can pollute nearby water sources. Most fertilizer schedules will recommend application rates between .5lbs and 1lb of nitrogen for the health of the lawn, but you can help prevent water pollution by using a slow-release fertilizer like compost.
The Difference Between Quick-Release and Slow-Release Fertilizers
There are three main components of fertilizer: nitrogen, phosphorus, and potassium. The king among these three is nitrogen.
A quick-release fertilizer makes all of the nitrogen available immediately upon application. Nitrogen is responsible for green top growth, so a large dose will result in quick, deep green growth that makes your lawn appear healthy for a short time.
These fertilizers will also release supporting nutrients, but phosphorus and potassium are not as easy for plants to absorb, so plants will absorb a disproportionate amount of nitrogen before they can take in adequate amounts of phosphorous and potassium. These nutrients help support root growth and other chemical processes that contribute to the whole plant structure.
Forcing a lot of green growth without a supporting root system will stress out your lawn and will require frequent reapplications to keep up a healthy appearance. The more often a quick-release fertilizer is applied, the more stressed your turf will be. Eventually, stress will lead to susceptibility to pests and disease.
A slow-release fertilizer makes small amounts of nitrogen available over a specific length of time. Small doses will result in a slow, controlled top growth during the growing season along with supporting nutrients to encourage root growth.
Slow-release fertilizers will not give your lawn a quick shot of lush, green growth. But, it will provide sustainable nutrition that supports your plants as a whole. This will result in a strong turf that resists pests and diseases (source).
Slow-release fertilizers can be synthetic or organic, but organic fertilizers provide many benefits that synthetic ones can’t. Compost is the best organic, slow-release fertilizer. It provides all of the 16 nutrients that plants need to thrive, plus it introduces beneficial microbes and compounds that support the overall health of the entire lawn. Compost also improves the texture of a lawn’s topsoil, which will help water and oxygen permeate the soil and aid in the decomposition of thatch.
Synthetic slow-release fertilizers are better than quick-release fertilizers but lack the benefits of organic options. The use of synthetics may require additional applications of nutrient-specific amendments, like chelated iron, to fix deficiencies.
How Fertilizer Influences Lawn Health
A lawn is a lot like a person. With the right nutrition, hydration, and physical maintenance, it’s easier to fight off disease and stay healthy. However, if your lawn has an imbalance of these factors, it becomes stressed, and its ability to fight off pests and diseases is weakened.
St. Augustine Growing Seasons
Balanced nutrition is at the core of a healthy lawn. Throughout the year, grass goes through stages of growth where it has different nutrient requirements.
St. Augustine breaks dormancy in mid-spring. During this greening-up period, the nutrient requirements are fairly low. Fertilizing during this time will encourage weak, unsustainable growth, which is a prime target for cooler-weather diseases like brown patch fungus.
St. Augustine takes off during the summer. Warm, humid environments are the perfect growing climate for St. Augustine. After you’ve mowed a few times, the lawn will be triggered to grow deeper roots and to send out runners to fill in bare patches of soil. This is the time to begin fertilizing.
During warm weather, when St. Augustine is actively growing, it needs a consistent supply of nitrogen, phosphorus, and potassium to grow deeper root systems, send out runners, and maintain new leaf growth. Consistent, vigorous growth helps the lawn resist pests and disease, and also helps it cope with potential drought conditions.
St. Augustine goes dormant once the soil reaches 550. As the lawn prepares for winter, nutrient requirements lessen. Fertilizing during this time will encourage weak, unsustainable growth that will be susceptible to disease.
St. Augustine is dormant during cooler temperatures. Plants, unlike animals, don’t need to store up much nutrition for the winter. Dormancy is a means of protection from cold temperatures that would otherwise kill the plant. Fertilizing near or during this time will make it difficult for the grass to stop active growth, which will make it susceptible to damage from insects, diseases, and cold temperatures.
Other nutrients, like iron, calcium, sulfur, etc., are equally important for the plant, but less important in a fertilizer. Each nutrient has a chemical makeup that determines how well it will bond to the compounds in the soil (cation exchange capacity).
It is nearly impossible for soil to hold on to nitrogen, which is why it is so easy for nitrogen to leach into water sources. However, other nutrients, like phosphorus, bond too well to the soil, meaning it doesn’t leach out, but it’s also difficult for plants to absorb it. Consistent applications of these nutrients maintain a healthy level of plant-available compounds.
Nitrogen, phosphorous, and potassium are absolutely crucial for plant growth and health and are also the most difficult nutrients to maintain in soil. This is why they are the star players in fertilizer, while the other 13 equally-important nutrients are all but ignored unless plants show signs of deficiency.
If you are looking for a natural lawn fertilizer that is safe for pets and children, be sure to read this article.
St. Augustine grows in warm, humid environments. During the summer, when it is actively growing, it needs consistent nutrition to keep up with growing deeper roots, longer runners, and replacing top growth lost from mowing.
During cooler weather, St. Augustine is susceptible to many different fungi and diseases that thrive in cool, moist environments. These diseases attack stressed lawns. St. Augustine goes dormant during cool weather, so a shot of fertilizer at the wrong time can force new, green growth when the plant is trying to rest. This green growth may look nice, but it’s a target for fungi, and the plant isn’t aggressive enough during this time of year to fight off disease.
Fertilizing & Irrigation
Nutrition and water go hand-in-hand. Plant roots have to absorb nutrients in order to use them, and then they have to circulate those nutrients throughout their system in order to utilize them.
This isn’t possible without an adequate amount of water. However, it’s also not possible if there’s too much water.
Roots need an equal amount of water and oxygen in order to absorb and use nutrients. Healthy irrigation schedules saturate the soil and then allow it to breathe.
Watering too frequently will leach nitrogen from the soil before the lawn is able to absorb much, meaning you’re washing time and money down the dirt. However, if you rely on mother nature to supply your irrigation, the fertilizer may sit and accumulate in sections of your lawn, and result in nitrogen burn when it finally sees some moisture.
Consistent, deep, infrequent irrigation is the key to healthy lawn growth and healthy use of applied fertilizers. For St. Augustine, water once per week for 45 minutes – 1.5 hours, depending on your soil structure. For clay soils, you may need to extend time between irrigation and for sandy soils, you may need to irrigate more often.
Thick thatch layers can restrict the amount of water that the soil can absorb, so spend time dethatching St. Augustine in the spring if your thatch layer has built up to over ½” and feels spongy.
Fertilizing & Mowing
Mowing puts calculated stress on your lawn, which encourages growth as a response. This is much like a muscle’s response to exercise; some tissue is broken down, so the body responds by rebuilding and strengthening the area. And, just like a muscle, a lawn can only repair itself if it has adequate nutrition.
The key to a healthy mowing schedule is to remove enough growth to trigger new growth, but not so much that the lawn is unable to recover. Follow the 1/3rd rule, but be sure to maintain a height of at least 2.5” for St. Augustine.
Bare patches of soil are prime real estate for weed seeds to germinate and take hold in your lawn. Most warm-season grasses spread out through above-ground runners and underground rhizomes, meaning they can be cut quite short and still fill in quickly. However, St. Augustine doesn’t have rhizomes, so it has to maintain enough top growth in order to send out runners to repair itself after mowing and to fill in bare patches of soil.
If you mow too short, St. Augustine will be constantly trying to get back to square one, instead of filling in your entire lawn and choking out weeds.
Keep in mind that the active part of the growing season for this turf is during the heat of summer, so most of your lawn’s ability to fight off weeds will be determined by your fertilizing/mowing schedule for mid-summer, even though weeds tend to germinate earlier and later in the season when the weather is cooler.
Fertilizing & Pest Management
Pests can be anything from weeds to insects to diseases. The driving factor behind pest management is a healthy lawn. Sick lawns get sick. If your lawn is malnourished, mowed at an improper height, or given too much/too little water, pests will find a way into your yard.
While many homeowners see the goal of fertilizing as having a nice looking lawn, the real goal is having a lawn that resists the pests that will make it look bad. All components of a maintenance schedule revolve around making it extremely difficult for pests to get comfortable in your lawn.
Insects, diseases, and weeds thrive in poor environments. If you create a healthy environment, pests are unable to thrive, and your lawn gets to enjoy a solid, nutritious foundation.
However, if you follow the wrong fertilization schedule, and try to over-fertilize in an attempt to make your lawn appear healthy, you will create a poor environment of weak growth. Poor environments breed pests, and you will constantly be fighting bugs, weeds, and fungi.
So, before you begin any maintenance schedule, make sure you are putting your effort into sustainable, healthy growth. Trying to force your lawn to green-up before it’s ready, stay green longer, or grow too much during the summer will only create the very issues that make your lawn look unhealthy, which defeats the whole purpose.
Fertilizers vs. Soil Conditioners
Compost is generally labeled as a type of fertilizer, and while it does provide nutrition, it’s actually considered a soil conditioner.
Conditioners are more than a quantifiable source of vitamins and minerals. They provide microbes, electrical charges, carbon, bulk, and other components of soil that fertilizers just don’t have. They increase the overall health of the soil, which makes fertilizers even more effective because it creates a healthy foundation for the lawn to grow into (source).
Compost is not applied like a fertilizer. Fertilizers are concentrated particles of nutrients, while compost is more of a system overhaul.
Apply compost as a topdressing in the spring and in the fall to help build up healthy topsoil and replace a few synthetic fertilizer applications.
St. Augustine Fertilizer & Maintenance Schedule
We’ve included a detailed maintenance schedule/tracker in our free printable download. But, for the abridged version, here’s the cliff notes:
- Before the lawn turns green (March): Get a soil test. Make plans to correct deficiencies/toxicities
- After the first mowing (March-May): Dethatch with a thatch rake if the thatch layer is over ½”. Topdress with ½” of compost.
- After the 3rd mowing (March-May): Fertilize with a slow-release fertilizer at the rate of 1lb – 1.5lbs per 1,000sq’ (depending on your soil). Apply a pre-emergent weed killer. Begin irrigating consistently; every 5-10 days as your lawn shows water stress.
- Every 10 weeks during the growing season: Fertilize with slow-release fertilizer at the rate of 1lb – 1.5lbs per 1,000sq’ (depending on your soil).
- 6 weeks before the first frost (September): Fertilize with a high-potassium, low-nitrogen fertilizer at the rate of .5lbs per 1,000sq’. Apply a pre-emergent weed killer.
- 4 weeks before the first frost: Stop irrigating unless the lawn is water-stressed. Topdress with ¼” of compost.
- October-February: Water as needed. Do not fertilize.
Water St. Augustine when the leaves get dark and your shoes leave footprints in the grass. Saturate the soil 6” deep.
Note: Always irrigate after fertilizing.
Start the season with a shorter mowing height (2.5”) and gradually increase to 4” before summer. Near the last fertilizer application of the year, begin decreasing the mower height to 2.5” so the lawn is shorter before dormancy. Don’t bag your clippings.
Sharpen your blade at least once per season.
Pre-emergent weed control kills weeds before they can germinate. This is important after fertilization because you don’t want weeds to take root and absorb all the nutrients that were meant for your lawn.
If you have established weeds, use a broadleaf weed killer, like 2-4D, and spot-treat your lawn as needed.
Compost is an extremely slow-release type of fertilizer, but it also helps with water retention and keeping pests at bay. Use a thicker topdressing in the spring and a thinner topdressing in the fall, when your lawn is about to slow down.
For a .5” layer of compost, use 1.5 cubic yards per 1,000sq’. For best prices, order compost from a local nursery supply company.
Healthy lawns are a product of careful planning and commitment. While all turfgrass maintenance has the same underlying principles, each yard is different, and every homeowner will have a different vision for their ideal lawn.
Climate zone, weather patterns, and proximity to the coast will affect the exact timing of certain maintenance tasks. Keep notes each year about what worked, what didn’t, and what you want to change next time. This way you can create a maintenance plan that is tailored to your lawn.
For more information on St. Augustine lawns, read these important articles:
- Dethatching St. Augustine
- St. Augustine vs. Bermuda
- St. Augustine vs. Centipede Grass
- St. Augustine drought tolerance.
Note: You can also use worm castings on your lawn as an organic lawn fertilizer.