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Zoysia is supposed to be one of the most aggressive warm-season grasses. In fact, it’s so aggressive that it’s supposed to choke out weeds so thoroughly that you don’t need to do much chemical weed control.
But, will zoysia choke out crabgrass? Zoysia can choke out crabgrass if the lawn is maintained properly. Extreme infestations require that you first spray and dig up existing plants, and then encourage zoysia to fill in bare patches through consistent irrigation, mowing, aeration, and topdressing.
Crabgrass is an ugly, frustrating weed. It’s a common problem in zoysia lawns, because zoysia is a grass that is usually ignored during the growing season.
A few crabgrass plants may go unnoticed, and they can quickly turn into hundreds if they are not removed or sprayed.
Zoysia vs. Crabgrass
The biggest difference between zoysia and crabgrass is that zoysia is a turfgrass while crabgrass is simply a weed.
Crabgrass is never grown on purpose and it has led to the development of many different crabgrass-specific herbicides.
Zoysia is a low-maintenance, warm-season turfgrass that thrives in hot, dry climates. Zoysia is extremely sensitive to cold winter temperatures, and it will go dormant as soon as temperatures reach 55 degrees.
Although zoysia is an aggressive turfgrass, it also goes dormant quickly after a week without moisture, which can slow its competitive growth against weeds. Consistent irrigation and a proper maintenance schedule will encourage zoysia to thrive, which is the key to helping it choke out weeds and other grasses.
Crabgrass is an ugly, conspicuous, yellow-green creeping grass that can be found throughout the United States. Although crabgrass has the word grass in its name, it is never a viable option for a turf grass.
Crabgrass is an annual weed that can put out over 150,000 seeds and 700 runners from a single plant (source). Crabgrass is classified as a warm-season grass because it thrives in hot, dry climates.
However, because it is an annual, crabgrass can grow in any climate; winter temperatures only affect how soon the plants die off. The seeds will stay dormant during the winter and sprout as soon as the soil temperature reaches 55-60 degrees.
It is easier to control crabgrass in cool climates where it has a shorter growing period and less-than-ideal growing conditions. The hotter and drier the climate, the more vigorous and stubborn crabgrass becomes.
Zoysia vs. Crabgrass: Growth Habit
Zoysia and crabgrass are both warm-season grasses, so they both send out stolons and rhizomes to spread.
However, crabgrass can fill in an area much quicker than zoysia because crabgrass also puts off viable seed that can germinate in as little as two weeks. Zoysia can also go to seed, but most of its seed will be sterile, so it does not help the lawn fill in any faster.
Zoysia comes out of dormancy in late spring. Mowing, irrigation, dethatching, aerating, and topdressing all begin in mid-April through May.
Once temperatures reach 55 degrees, which is usually in or near October, zoysia goes dormant for winter.
In a weed-free lawn, zoysia should be fertilized during the summer when the turf is actively growing. Consider a natural lawn fertilizer to prevent the accumulation of chemicals in the soil from long-term use.
However, summer fertilization gives crabgrass a boost of energy, so it’s best to avoid this until the crabgrass is under control.
Instead, focus on core aeration and topdressing with a high-quality compost each spring. This will slowly build up a healthy, fertile soil, which gives zoysia a good foundation to establish a strong root system.
Zoysia can thrive without annual fertilization as long as the soil drains easily and has some organic material.
Crabgrass seeds can begin to germinate weeks before zoysia breaks dormancy. This is good news for homeowners, because during this window, it’s open season on crabgrass.
As long as zoysia is still dormant, you can spray herbicides that will only affect crabgrass.
Crabgrass spreads through rhizomes and stolons, but it takes over a lawn by reseeding itself in huge numbers. While you may kill off the plants during the growing season, seeds from previous years can still germinate and take back over in a matter of weeks.
The key to eradicating crabgrass is to prevent the grass from going to seed by killing the seedlings each spring and summer as they germinate. While the mature plants are ugly, they are relatively harmless until they go to seed.
Crabgrass can withstand more severe drought conditions, poorer soil, and shorter mowing heights than zoysia. If a zoysia lawn is neglected, crabgrass will quickly take over as zoysia suffers.
Crabgrass Control In A Zoysia Lawn
Crabgrass is most vulnerable in the spring before it has had a chance to go to seed. In order to eradicate a crabgrass infestation in your lawn, you must use both chemical and manual control methods.
Chemical Crabgrass Control
There are two types of chemical control for weeds: pre-emergent herbicides and post-emergent herbicides. Pre-emergents prevent seeds from germinating, while post-emergents kill living plants.
Crabgrass Control With Pre-emergent Herbicides
Pre-emergents are used on lawns where seeds are present, but have not germinated. They are applied in the spring as temperatures warm and become ideal for germination.
Most pre-emergents are active for 2-3 months after application, so they can be applied in February/March and then again in April/May to prevent dormant seeds from germinating.
Pre-emergents are not selective, which means they will kill all seeds before they can germinate.
Some homeowners overseed a cool-season grass on their zoysia lawn so the grass greens up earlier in the spring. If you have an active crabgrass infestation, make sure you eradicate the weed from your lawn before you decide to overseed your zoysia lawn with a cool-season grass.
Crabgrass Control With Post-emergent Herbicides
Post-emergents kill living plants. Weeds are classified as either broadleaf or grasses. Selective herbicides are targeted towards plants with similar growth habits. Broadleaf weed killers are safe on lawns because they target plants with a very different growth pattern.
Grasses can be more difficult to spray for, because weedy grasses have the same growth habits as turf grasses.
Be careful to purchase herbicides that are formulated for crabgrass, or else you will kill the turf you want to keep. Ortho Weedclear (link to Amazon) is designed to kill crabgrass while being safe for Zoysia lawns.
Post-emergents can be sprayed throughout the growing season, but focus on killing active plants before they are able to go to seed, which is usually in late summer.
Manual Crabgrass Control
Chemical control will keep most crabgrass infestations in check, but in order to completely eradicate the weed, you need to combine chemical control with manual control.
Crabgrass Control: Manual Removal
It’s usually not a good idea to pull warm-season grasses because they can regrow from roots left in the soil. However, because crabgrass is an annual, manually removing crabgrass can be an effective control method.
Even if the grass comes back, it may not have time to go to seed, which drastically reduces the following year’s population.
Dig out the grass and as much of the root system as possible. Irrigate after digging up crabgrass to encourage zoysia to fill in bare spots.
You may also spray a pre-emergent after manual removal to prevent dormant seeds from germinating in new bare spots.
Crabgrass Control: Healthy Maintenance
The best way to control weeds in your lawn is to maintain healthy growth through consistent maintenance practices. Encourage your zoysia lawn to fill in and choke out crabgrass by mowing at the proper height (.75”-1.5”), irrigating .5”-1” per week, and aerating and topdressing each spring.
With proper maintenance practices, zoysia will be able to choke out crabgrass once it has established a healthy root system, which can take 2-3 years after planting.
Crabgrass is a frustrating, aggressive weed, but after a few years of consistent control practices, you can have a weed-free, healthy zoysia lawn.
For more information on zoysia, read Thriving Yard’s articles on zoysia vs. fescue, and how to grow zoysia in clay soil.