Oddly, dethatching St. Augustine grass is a hotly-debated question in the horticulture world. Of course, it’s possible to dethatch any lawn. The real question is: should you?
The reason this is such a touchy subject is that you should dethatch St. Augustine before you need to use a machine, which can destroy the grass. But, most people don’t recognize a thatch problem until it is severely restricting growth. Use dethatching rakes, core aeration, and healthy maintenance practices to keep thatch at a manageable height.
Don’t worry- even if you have a sizable thatch buildup, there are ways to remove it without completely destroying your lawn. However, you should be prepared to do some damage control.
What Is Thatch?
Thatch is the layer of dead plant material that settles on top of the soil. Most thatch is from dead grass clippings that build up throughout the summer, but dead leaves, pine needles, and other plant material can contribute to a thatch layer.
If the thatch is under 1/2” thick, it is actually beneficial for your lawn. A thin layer of dead plant material will help retain moisture, and as the leaves decompose, they return nutrients to the soil. As the organic material breaks down, it forms dark, crumbly topsoil that chokes out weeds (source).
However, thatch will only break down in a healthy, properly-maintained lawn. Like compost, a thatch layer will only decompose if it is moist, warm, and aerated.
To keep your thatch layer at a manageable height, use the following maintenance practices:
Use a deep, infrequent irrigation schedule. Water once per week for 45 minutes – 1.5 hours, which will saturate the soil and keep thatch moist enough to decompose.
Use a core aerator in the spring. Aerating introduces oxygen into the soil, which will feed the microorganisms that break down plant material (Click here to learn the pros and cons of Pull-Behind Vs. Rental Aerators).
Use a mulching blade, and follow the 1/3rd rule. Thatch breaks down easier if the grass clippings are small, so use a mulching blade and mow twice per week, never cutting off more than 1/3rd of the growth.
If you already have a few inches of thatch buildup, you can encourage decomposition by changing your maintenance practices. You may even be able to avoid renting a power dethatcher after a growing season of healthy upkeep.
When Should A Lawn Be Dethatched?
Dethatching should be done once your lawn has broken dormancy and begun to actively grow. Once your grass has grown enough to need to be mowed, it can handle dethatching. For St. Augustine, this will be in mid to late spring. A thatch rake can be used during most of the growing season since it does not harm the stolons, but you still want to leave enough time for a small layer to build up before dormancy.
Why Do People Say To Not Dethatch St. Augustine Grass?
There are two settings for a power rake: a wide setting for bunch grass, and a narrow setting for sod-forming grass. Most sod-forming grasses spread through above-ground stolons and below-ground rhizomes. If you cut through and remove a majority of the runners above ground, the grass will regenerate from the rhizomes down below.
St. Augustine is a sod-forming grass, but it doesn’t have rhizomes. Therefore, if you use a power dethatcher, you will end up removing most of the top growth, which is how it spreads and fills in bare patches of soil. Dethatching is generally paired with a very low mowing height, but St. Augustine struggles if it’s cut under 2.5”.
If you take off a considerable amount of top growth and cut the remaining growth to 1”, your lawn will have little chance for survival. So, most professionals advise against dethatching to prevent needing to completely replace your lawn. However, what they’re really advising against is using a power rake, not the act of removing thatch.
Dethatching St. Augustine With A Hand Rake
The best way to prevent the need for a power dethatcher is to use a hand thatch rake (link to Amazon). Again, wait until your lawn has actively started growing.
Note: this is not the same as a leaf rake: See Can You Dethatch A Lawn With A Leaf Rake? Dethatching Options
Irrigate your lawn the day before you rake. Dethatching works best when the clippings are moist. Mow St. Augustine to 2” so the thatch is easier to access. This is too low for regular mowing, but not so low that it can’t recover.
Use the hand rake to pull the thatch layer up to the surface. If it comes up easily, you can rake it into piles and remove it. However, if it’s deep and compacted, you may have to rake up what you can, and then go over the lawn again with a mower. Use a bag to collect the clippings and loose thatch.
Continue to remove thatch until you can see the soil. Although ½” of thatch is healthy in most lawns, the bottom ½” of a thick thatch layer will be compacted and too thick to break down quickly. It’s best to remove as much as you can and let a small layer accumulate naturally.
Power Dethatching St. Augustine
There are two machines that you can rent for dethatching: a dethatcher, and a power rake.
A dethatcher is less aggressive, and is the best machine for St. Augustine. It will be a machine or attachment that uses tines to pull thatch up from the surface. It’s not nearly as damaging to the stolons, and your lawn will recover quicker.
A power rake is the most aggressive dethatching machine, and it will probably destroy your St. Augustine lawn. Most hardware stores use “dethatcher” and “power rake” interchangeably, so make sure you don’t accidentally rent a power rake when you’re looking for a dethatcher. A power rake will cut into the grass and down into the soil to break up thick layers of thatch.
The main difference between a dethatcher and a power rake is that a dethatcher is for prevention, while a power rake is a solution.
Irrigate your lawn deeply the day before dethatching to help break up tough layers. Mow your lawn short (some dethatchers come as attachments to your mower, so you can do it in one step).
Run the dethatcher across your lawn as you would a mower, and pick up the dislodged plant material. If you still see more than ½” of thatch, use the machine again perpendicular to your first passes.
If your lawn has a substantial thatch buildup (more than a few inches) it may be time to start over. Power raking is quite labor-intensive, and large thatch layers generally sit on top of compacted soil. Ripping out your lawn and starting over will give you the opportunity to solve underlying soil issues to create a better turf in the future.
What To Do After Dethatching St. Augustine
After dethatching, your lawn will be stressed and in shock. For the next several weeks, the grass will attempt to heal and fill in bare spots. Get your lawn off to the best start by beginning preventative maintenance and providing the nutrition your grass needs to heal.
Be sure to read How To Clean Up After Dethatching: A Practical Guide
Fertilize after dethatching. Your lawn has likely been starved for nutrients due to a thick thatch layer that acts as a filter. Now that you have removed the thatch, the soil can absorb the nutrients that your lawn needs to grow. Use a slow-release fertilizer that is equal parts nitrogen, phosphorus, and potassium so your lawn can begin recovering.
Irrigate after dethatching. A thatch layer provides protection against moisture evaporating from the soil. Now that you have removed that layer, water will evaporate very quickly until the new grass fills in. Your grass will also be absorbing fertilizer and putting a lot of energy into new growth, so it will use more water than normal. Continue to irrigate deep and infrequent, but you may need to irrigate longer or decrease the amount of time between watering.
Treat for weeds after dethatching. Bare soil is an open invitation for weed seeds. Don’t let your time spent dethatching go to waste by allowing broadleaf weeds to take over. After dethatching, put down a pre-emergent weed killer to make sure weeds seeds can’t germinate while the St. Augustine fills back in.
Continue to mow after dethatching. Mowing encourages your lawn to keep growing. The main concern after dethatching is root growth because healthy roots create healthy lawns. Work your way up to a 4” mowing height gradually, but continue to mow every 4-5 days after dethatching to keep encouraging new growth.
Implement a soil-improvement plan after dethatching. Thatch buildup can either cause or was caused by, poor soil. Compacted soil will make it difficult for dead plant material to break down and incorporate into the topsoil, so take a moment after dethatching to collect some soil samples and get a soil test at your local extension office. Use compost to topdress your lawn at the beginning and end of each growing season to improve texture.
Once you have a healthy, thriving St. Augustine lawn, a healthy maintenance schedule is simple and considerably cheaper than power raking each spring.
Recommended Next Read: Will St. Augustine Choke Out Bermuda Grass?