Aztec grass (Ophiopogon japonicus ‘Aztec Grass’) is a popular ornamental plant with striking variegated foliage. Its green and white striped leaves form tidy, clumping mounds, making it a favored choice for edging pathways, mass plantings, or adding texture in garden beds. Understanding its ability to withstand cold temperatures is important for its longevity and vibrant appearance.
What Cold Hardiness Means
Plant cold hardiness refers to a plant’s capacity to endure low winter temperatures. The USDA Plant Hardiness Zone Map is the primary tool for assessing this, dividing regions into zones based on average annual extreme minimum winter temperatures.
Each zone represents a 10-degree Fahrenheit difference, with lower numbers indicating colder regions. Each zone is further subdivided into ‘a’ and ‘b’ segments, denoting a 5-degree Fahrenheit increment. This system helps gardeners select perennial plants likely to survive winter in their location.
Aztec Grass Hardiness Zones and Limits
Aztec grass is hardy in USDA Plant Hardiness Zones 6 through 10 or 7 through 11. This broad range indicates its adaptability to various winter climates. For example, Zone 6 experiences average minimum temperatures between -10°F and 0°F, while Zone 10 ranges from 30°F to 40°F.
When temperatures drop below Aztec grass’s hardiness threshold, foliage can suffer damage, often appearing as browning or dieback. In severe cases, especially in zones colder than its recommended range, Aztec grass may only survive as an annual plant. However, even with top growth damage, Aztec grass frequently recovers from its roots once warmer spring temperatures arrive.
Winter Protection for Aztec Grass
Protecting Aztec grass in colder climates or during unexpected cold snaps helps ensure its survival. Apply a thick layer of mulch, at least 2 inches deep, around the base of the plants to insulate roots from freezing temperatures. Apply mulch once the ground has sufficiently frozen to prevent the plant from remaining active during winter.
Ensuring adequate moisture before a freeze is beneficial, as water in the soil helps retain heat, protecting the roots. For extreme cold, covering plants with materials like burlap or frost cloth provides additional insulation. These covers should extend to the ground to trap warmer air and be removed during the day to prevent overheating.
Caring for Cold-Damaged Aztec Grass
If Aztec grass experiences cold damage, foliage may appear brown, mushy, or withered. Resist the urge to prune immediately after a freeze. Waiting until new spring growth emerges allows for a proper assessment of which parts of the plant are truly dead.
Once new shoots appear, the dead or severely damaged foliage can be trimmed back. This can be done by shearing or mowing the plant down to about three inches from the ground, or by hand-trimming browned tips. Aztec grass is resilient and often recovers well from the roots, even if all above-ground foliage is damaged.