Zoysia and St. Augustine grasses are both warm-season turf varieties that thrive in the heat and humidity of the Southern United States. Homeowners often desire the dense, fine-bladed texture of Zoysia or the lush, broad-leaf coverage of St. Augustine for their lawns. While both are adapted to similar climates, their differences in growth habit and maintenance requirements make them unsuitable for a harmonious coexistence in a single lawn area.
The Competitive Nature of Mixing Zoysia and St. Augustine
The primary obstacle to successfully mixing Zoysia and St. Augustine lies in their aggressive and differing growth patterns, which leads to a biological battle for dominance. Both species are creeping grasses, but Zoysia spreads using both underground stems (rhizomes) and above-ground runners (stolons), creating a dense, mat-like turf. St. Augustine, however, relies almost exclusively on thick, fast-spreading stolons to cover ground rapidly.
When planted together, the result is not a blended lawn but a patchy, uneven turf where one species quickly outcompetes the other. St. Augustine often gains an initial advantage due to its rapid lateral growth. Conversely, Zoysia’s dense root and rhizome structure allows it to form a thick canopy that can choke out the St. Augustine over time, especially if mowed at a lower height. This competition means the mixed lawn will eventually devolve into a mottled appearance as the two grasses struggle for resources.
Key Differences in Maintenance and Aesthetics
Maintaining a mixed lawn presents conflicting needs that make proper care difficult for the average homeowner. The required mowing height is one of the most significant differences for optimal health. Zoysia grass is typically maintained at a lower height, often between 1 and 2 inches, to encourage its dense growth pattern. St. Augustine, with its coarser blades, must be cut much higher, generally between 3 and 4 inches, as mowing it too low severely stresses the plant and exposes its fragile stolons.
Setting a mower to a compromise height, such as 2.5 inches, weakens both species. Zoysia will not achieve its full density, and St. Augustine will be scalped, making it vulnerable to heat stress, pests, and disease.
Another conflict arises from their differing light requirements. St. Augustine has superior shade tolerance compared to Zoysia, which prefers full sun. In a mixed lawn, shaded areas will favor St. Augustine, while sunny spots will allow Zoysia to thrive, resulting in uneven thinning and color variations across the yard.
The aesthetic differences further contribute to the lack of uniformity of a mixed turf. Zoysia is known for its fine-to-medium-textured blades, which create a plush, carpet-like appearance. St. Augustine has a much coarser texture with noticeably wider blades, giving it a more open and lush look. The contrast in blade width, density, and color between the two grass types is immediately noticeable.
Strategies for Lawn Monoculture
Since mixing the two species is not conducive to a healthy, uniform lawn, homeowners must commit to a single species. If a lawn is already mixed, transitioning entirely to St. Augustine is often the easier path due to its aggressive growth habit and superior ability to spread. This transition can be accelerated by vertical mowing the Zoysia patches to open up the canopy, followed by plug planting or sprigging St. Augustine into the newly exposed soil.
Transitioning to a pure Zoysia lawn is generally more challenging and requires more direct intervention to remove the resilient St. Augustine. Homeowners can employ selective herbicides, such as those containing quinclorac or Fusilade II, which are known to suppress St. Augustine without significantly harming Zoysia when applied correctly. This method requires careful application and may need multiple treatments over a growing season to completely eliminate the St. Augustine.
For a faster and more complete conversion, the most effective method is a full lawn renovation, which involves using a non-selective herbicide like glyphosate to kill all existing vegetation. After the previous turf is completely dead, the area can be re-sodded or sprigged entirely with the chosen Zoysia variety. The final choice between Zoysia and St. Augustine should be based on the specific environmental conditions of the yard, prioritizing factors like shade cover and the homeowner’s desired maintenance level.