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Crabgrass is an unattractive weed that seems to live and spread forever once it gets started in a yard. In some cases, weeds can be “choked out” by a healthy lawn. Centipede grass is very sensitive to some herbicides so it may be tempting to try and allow it to choke out the crabgrass.
Will centipede grass take over crabgrass? It is possible for centipede grass to take over crabgrass with proper watering and fertilization, but unlikely. The better solution is to keep the lawn healthy to prevent new growth use herbicides specifically recommended for centipede lawns to kill existing crabgrass.
Centipede grass is known for its excellent heat tolerance and extremely low maintenance requirements — a favorite of lawn owners interested in minimal upkeep. However, centipede grass has very specific climate and soil requirements that can make the prevention and elimination of crabgrass more difficult. It will take planning to have a centipede grass lawn free of crabgrass.
Characteristics of Centipede Grass
Centipede grass is Granny Smith apple green in color. Over-fertilization with nitrogen to make it a darker green will lead to several different problems, including increasing maintenance and decreasing cold hardiness. Centipede grass likes acidic soil that many other kinds of grass would not be able to tolerate.
Centipede grass does not go dormant in the winter, so it is not cold hardy. It does best in zones 9-10. It is tolerant of the heat and has moderate drought tolerance. It needs six hours of sunlight a day but can handle some moderate shade.
Centipede grass spreads by stolons. This means that it spreads on the surface and not through its root system. This results in slow-growing, slow-spreading lawn. It is likely any bare spots will have to be overseeded as they fill in very slowly. However, it also means that centipede grass does well near flower gardens as it will not spread under the borders.
Preventing Crabgrass
Crabgrass is very difficult to kill once it gets started in your yard. Crabgrass is annual, so it only lives and grows for one year. In that year, it can do enough damage in a yard to have long-lasting consequences. It is important to understand the life cycle of crabgrass to prevent or eliminate it from a lawn.
Cycle of Crabgrass
Crabgrass is a warm-season annual. It has a life cycle that spans one year or growing season. However, during that time, it can produce 150,000 seeds making it very likely to re-seed itself and to appear on the same lawn again next year. Some of the typical non-herbicide lawn treatments, such as mowing the lawn short, will not help because of the number of seeds.
Once crabgrass has started growing in a lawn, the seeds will continue to germinate all growing season. Each crabgrass plant will grow to about a foot in diameter. The newest research has identified chemicals in the crabgrass that actually inhibit other plants, allowing it to expand and choke them out.
Crabgrass will begin dying at the first frost, and by winter, it will be gone leaving behind a bare dirt patch. These patches can be a foot in diameter. Overlapping circles may leave large areas of the lawn bare or very sparse. The next season before the regular lawn grass can fill this circle in; the new crabgrass will sprout from seed.
Mowing Conditions
The first priority to preventing crabgrass is to have a nice, thick, healthy lawn. The healthier and thicker the lawn, the less chance crabgrass seeds have to take root. Careful mowing can help create a lawn that is healthier and less susceptible to crabgrass. Mowing a lawn too short can lead to a thin, sparse or sickly lawn that provides great growing conditions for crabgrass.
Crabgrass needs sun and soil temperatures above 55 degrees to germinate. Mowing lawns taller will help create conditions that are less likely to germination crabgrass seeds. Taller lawns also help keep the soil cooler and keep sunlight from reaching the soil. Centipede grass does well even if mowed to a height of 2 inches, helping with making the lawn taller.
After mowing, it is important to take care when using edging tools or weed eating. When clipping back the grass along pathways and borders, do not scalp the edges of the lawn. This will lead to thin or bare spots, creating the perfect place for crabgrass seeds to germinate.
Other lawn care tips include
- Mowing with sharp blades
- Never mowing when the grass or the soil is wet
- Use a mulching mower
- Never mow centipede grass below one inch.
Watering
A lawn that is overly dry is susceptible to crabgrass. Many lawn owners wait until their lawns are very dry. This is often late spring or early summer, right when crabgrass is about to sprout. Waiting to water leaves the grass dried out and thinner, creating the sparse conditions that allow crabgrass to take root. The grass may even be slightly dormant.
The homeowner then soaks the lawn thoroughly. The regular grass will take time to recover. During that time, the crabgrass will be sprouting and growing before the regular grass has thickened up. The result is grass that is stressed and crabgrass that is growing.
Centipede grass needs careful watering. If watered too lightly and frequently, it will develop a very shallow rooting system. Watering ahead of the typical time frame for crabgrass sprouts and then allow the grass to dry out, as usual, can help. Centipede grass does need to dry out (but not the point of thinning) to help control the crabgrass without damaging the centipede grass.
Seeding
Seeding can help keep a lawn thick. A thick lawn does not have thin or bare spots where the crabgrass can take root. Centipede grass does not spread rapidly. Bare spots need to be seeded to prevent crabgrass. Seeding in the spring will help to prevent crabgrass. Seeding in the fall will help fill in any bare spots created by the crabgrass after it dies but is not usually recommended since Centipede seeds will not germinate over the winter and you run the risk of them being washed away.
Fertilizer
Since having a thicker yard is often a way to prevent crabgrass, many places will state early and often applications of fertilizer will assist in deterring crabgrass. The problem with this possible remedy is that Centipede grass does not do well with over-fertilization. In early spring, this can lead to fast growth that dies back with a late frost creating bare spots in the yard for crabgrass.
Over-fertilization, especially with nitrogen, can also lead to long term damage to Centipede grass. This damage can leave a yard thin and sparse with bare spots. This opens the door to crabgrass. Over-fertilization can also change the pH in the soil and further weaken the Centipede grass. The key is to do regular fertilization meeting the lawn’s needs.
Soil testing is an important part of any fertilization program. This is especially true with Centipede grass due to its specific needs. Spending some time and money on soil testing can potentially save on time and money using a fertilizer that is not needed and repairing the damage.
Pro tip: I have put all of this worrying about the right type of fertilizer to rest using a natural lawn fertilizer that is customized to my soil’s needs.
Pre-emergent herbicide
If crabgrass was a problem in the past year, a pre-emergent herbicide could be used in the early spring to prevent seed germination. Centipede grass is sensitive to some herbicides. So, care needs to be taken to make sure the grass is able to withstand the treatment. Otherwise it the herbicide will kill not just the weeds, but the whole lawn.
When using a pre-emergent herbicide, make sure it is one designed to kill crabgrass as it is resistant to many of the herbicides on the market. Centipede grass is especially sensitive to herbicides during its “green up” time, so try and wait until it is fully green before applying. However, it is important to apply it before soil temperatures reach 55 degrees.
Prodiamine 65, commonly referred to as “Barricade”, is a pre-emergent liquid herbicide that is frequently used in centipede lawns. In fact, Centipede is listed as a tolerant turfgrass for Prodiamine by the University of Texas Institute of agriculture (source).
You can check the latest pricing for Prodiamine on Amazon or purchase from a local lawn and garden store.
You can also obtain Prodiamine in granular form for spreading with a broadcast spreader. Just be sure to water after applying to activate it.
When applying a pre-emergent herbicide, wait 60 days and two mowings before overseeding any bare or thin area that has been treated with herbicide. Centipede grass should never have a 2, 4-D herbicide. Always read the label and use caution when applying any herbicide. In some areas, you can find herbicides specifically labeled safe for centipede grass.
Post Emergent Herbicide For Centipede Grass
Crabgrass can take root in even the most cared-for yard. Once it does, a pre-emergent herbicide will no longer be effective. A post-emergent herbicide designed for crabgrass will be needed. Care will need to be taken to ensure that any herbicide used will not kill the centipede grass. Otherwise, the lawn will develop bare spots where the crabgrass can take root again.
Best post-emergent herbicide for centipede grass: The most effective post-emergent herbicides for use on centipede grass are Tenacity (mesotrione), Solitare (quinclorac + sulfentrazone), and Pylex (topramezone). These herbicides are specifically formulated to attack crabgrass and are approved for use on Centipede lawns.
Source: University of Tennessee Institute of Agriculture
Links to Amazon for these herbicides:
Note: Herbicides can be either selective or nonselective. Herbicides that are non-selective will kill most plants and should not be used on lawns. Herbicides that are selective will only kill specific plants as listed on their label. This is why it is especially important to use the correct product.
Many herbicides that are labeled for lawn use are selective and designed to kill broadleaf weeds, such as dandelions and thistles. They will not kill grasses. Since crabgrass is, however, a form of grass, many of those herbicides will not kill it. Other herbicides are formulated to kill grassy weeds, but they could potentially kill not just the crabgrass, but the entire lawn.
It is very important to read the labels and use only products that are recommended for use on Centipede lawns. For example, BioAdvanced All-in-One Lawn Weed & Crabgrass Killer is a popular spray for crabgrass but the manufacturer’s website specifically states that the product is not for use on Centipede lawns (source).
With proper watering and fertilization, it is possible for centipede grass to “choke out” the crabgrass. But this is not likely. In fact, crabgrass tends to be so hearty that it can actually overtake sections of Centipede. With some care and planning, though, Centipede grass can be kept free of crabgrass.
If you have a lot of larger growth areas, the herbicide you may need to use is a bucket and a pair of kneepads.
Physically removing the crabgrass is sometimes the first step to getting this stuff under control.
Improve Soil To Help Centipede Fight Crabgrass
Crabgrass loves compacted soil like clay but it will grow in almost any soil type. It can be grown in very dry conditions and over-wet conditions. Aerating clay soil will help relieve compaction and can improve centipede growth. This will need to be postponed if a pre-emergent herbicide was applied. Disturbing the soil after application will break the barrier designed to stop the seeds from germination.
Crabgrass can grow in very acidic soils, down to a pH of 4.8. One common way to decrease crabgrass is to raise the pH of the soil by adding lime. However, this will not work for Centipede grass as it also needs acidic soil. Centipede grass prefers soil pH of 5.5-6, so it can be raised if needed to these levels. Soil testing is important to ensure it does not raise any higher.
You should take steps to improve your soil so that the centipede can flourish, thereby reducing opportunities for crabgrass to take root. The healthier your centipede grass, the less likely it is to be overtaken with crabgrass.
Conclusion
It is unlikely that centipede grass will choke out crabgrass on it’s own, but with the help of pre-emergent and post-emergent herbicides, proper watering, soil conditioning, fertilizing, and reseeding of bare spots, you can create an environment in your lawn that is unwelcoming to crabgrass. The thicker and heartier your centipede grass, the less likely you will have issues with crabgrass.
Be sure to read our guide on Centipede Grass Care By Season to ensure that you are providing the nutrients and soil conditions necessary for your centipede lawn to thrive.