Zoysia grass is a popular choice for lawns due to its dense, carpet-like appearance and drought tolerance. However, Zoysia has a specific sensitivity to certain chemicals and management practices, making weed control challenging. Applying the wrong product or using correct products at the wrong time can severely damage the turf. This article provides safe, effective strategies tailored to Zoysia grass to eliminate unwanted weeds without causing harm.
Essential Timing for Zoysia Weed Control
The timing of weed control application is the most important factor for protecting Zoysia turf. Zoysia is a warm-season grass that turns brown during winter dormancy. Herbicides applied when the lawn is fully dormant are generally safer because the grass’s biological processes are significantly slowed.
Applying herbicides during the transition periods—spring green-up or fall slow-down—can be highly detrimental. During these times, the grass is actively diverting energy, making it highly susceptible to chemical damage. Always wait until the Zoysia is fully green and actively growing before applying post-emergent products.
Before treatment, correctly identify the target weed as either an annual or a perennial species. Annual weeds complete their life cycle within one year and are best controlled with pre-emergent products. Perennial weeds live for multiple years and require targeted post-emergent applications once they are actively growing.
Selective Chemical Strategies Safe for Zoysia
Chemical weed control relies on distinguishing between pre-emergent and post-emergent herbicides. Pre-emergent herbicides create a chemical barrier in the soil, preventing weed seeds from germinating. These products are the primary defense against common summer annual weeds like crabgrass, goosegrass, and foxtail.
The correct application window for pre-emergent products is determined by soil temperature, not the calendar date. Applications should occur when the average soil temperature consistently reaches 50 to 55 degrees Fahrenheit for several consecutive days. Applying the product too late, after weed seeds have sprouted, renders the treatment ineffective. A second application in the fall, when soil temperatures drop below 70 degrees Fahrenheit, prevents winter annuals like Poa annua and chickweed.
Post-emergent herbicides kill weeds that are already visible and actively growing. When selecting these products, confirm the label explicitly states they are safe for use on Zoysia grass. Many broadleaf weed killers contain a combination of active ingredients to target a wide spectrum of weeds.
Look for products containing active ingredients such as 2,4-D, dicamba, and mecoprop (MCPP), which Zoysia generally tolerates when used according to label directions. These combinations effectively control common broadleaf weeds like clover, dandelion, and plantain. For grassy weeds that have already emerged, quinclorac is a commonly used and tolerated active ingredient.
Specific perennial weeds, such as nutsedge, require a specialized post-emergent product. Look for ingredients like halosulfuron-methyl or sulfentrazone. Always spot-treat isolated patches of weeds rather than applying a blanket treatment when using these stronger formulations. Avoid any product not explicitly labeled for Zoysia use, as the turf is highly susceptible to phytotoxicity.
Non-Chemical and Cultural Suppression Methods
Physical removal remains a direct and reliable method for addressing isolated weed issues without chemicals. Hand-pulling is most effective for newly sprouted weeds or those with shallow root systems, especially when the soil is moist after rain or deep watering. Removing the entire root structure prevents regrowth.
Cultural practices suppress weed growth by maximizing Zoysia turf density. Mowing height should be kept relatively high, typically between one to two inches, allowing the dense blades to shade the soil surface. This shading reduces the sunlight available for weed seeds to germinate. Never remove more than one-third of the grass height in a single mowing session, as this stresses the turf and gives weeds a competitive advantage.
Proper watering techniques also discourage common weeds. Zoysia should be watered deeply and infrequently, encouraging the grass to develop deep, robust root systems. Shallow, frequent watering keeps the soil surface constantly moist, creating an ideal environment for shallow-rooted weeds to thrive.
Horticultural vinegar, a natural alternative, can be used as a non-selective spot treatment to desiccate weeds. This product contains a much higher concentration of acetic acid than household vinegar and rapidly burns the foliage. Extreme caution is necessary when applying horticultural vinegar, as it will also damage or kill any Zoysia grass it contacts.
Long-Term Lawn Health for Weed Exclusion
The most effective long-term strategy for weed exclusion involves creating an environment where Zoysia grass can thrive and naturally crowd out intruders. This begins with periodic soil testing to determine its pH level and nutrient balance. Adjusting the pH to the optimal range for Zoysia (generally slightly acidic to neutral) improves nutrient uptake and turf vigor.
A proper fertilization schedule ensures the Zoysia has the energy to maintain density. Fertilization should coincide with the grass’s peak growth periods in the late spring and mid-summer. Applying a controlled amount of nitrogen encourages lateral growth and dense coverage, leaving less space for weeds to germinate.
Aeration and dethatching are mechanical processes that alleviate soil compaction and remove thatch. Compacted soil restricts root growth and nutrient absorption, weakening the turf and making it susceptible to weed invasion. Dethatching removes excessive thatch buildup, allowing water and nutrients to reach the root zone more efficiently.
By addressing the underlying health of the Zoysia lawn—improving soil conditions, feeding it correctly, and managing compaction—the turf naturally becomes a dense, competitive surface. A thick, healthy stand of Zoysia is the most sustainable, long-term defense against common lawn weeds.