Centipede grass is a popular choice for warm-season lawns across the Southern United States due to its minimal maintenance requirements. Known for its distinctive apple-green color, this turfgrass thrives in poor, sandy soils. When centipede grass takes on a reddish or purplish hue, it signals that the turf is under stress. This visible change indicates a physiological disturbance caused by the grass’s environment or soil chemistry.
Reddening Due to Phosphorus Deficiency
The appearance of red or purple coloring is often a direct result of a deficiency in phosphorus (P), a macronutrient essential for energy transfer within the plant. Insufficient phosphorus disrupts metabolic processes, slowing the grass’s ability to use sugars produced during photosynthesis. This carbohydrate backup triggers the production of anthocyanin, a red or purple pigment usually hidden by chlorophyll. The accumulation of this pigment causes the leaves, particularly older tips or margins, to display the reddish color. Although centipede grass requires lower nutrient levels than other turf types, a phosphorus deficiency causes this marked change in coloration and stunts growth.
Environmental Triggers and Seasonal Changes
Not all reddening is due to chronic nutrient deficiency; environmental stressors can also temporarily induce anthocyanin pigments. Cold stress is a common non-nutrient cause, especially during early spring green-up or late fall dormancy preparations. Centipede grass is sensitive to temperature fluctuations, and cold snaps temporarily inhibit root activity and nutrient uptake. This slowdown in absorption, even when nutrients are present, mimics the effects of a true deficiency. Severe drought stress can also cause a reddish-purple tint as the plant conserves resources. When the weather stabilizes and temperatures rise, the grass often recovers its normal color without intervention.
Addressing Soil pH and Nutrient Availability
A chronic nutrient deficiency in centipede grass is often rooted in improper soil chemistry, particularly the soil’s pH level. This turf is an acid-loving grass, thriving in a narrow range, ideally between 5.0 and 6.0. If the soil pH rises above this range, becoming neutral or alkaline (above 6.5), the availability of essential nutrients, including phosphorus and iron, is severely reduced. This is known as nutrient lockup, where nutrients are chemically present but unavailable for root absorption. The inability to absorb phosphorus due to high pH is a frequent underlying cause of red coloration in established centipede lawns.
Soil testing is the most reliable method to confirm if the pH is too high and determine the exact level of phosphorus deficiency. Centipede grass is also sensitive to excessive phosphorus, which can interfere with the uptake of micronutrients like iron, leading to yellowing. Therefore, applying phosphorus without a confirmed soil test can create new problems, even if red symptoms are present. The primary goal is ensuring the soil environment is acidic enough to make existing nutrients accessible to the grass.
Actionable Steps for Lawn Recovery
The first step toward recovery is getting a professional soil test to determine the exact pH and nutrient levels. If the test reveals a high pH, the long-term solution is gradually lowering the soil acidity using elemental or granular sulfur. Sulfur works slowly, relying on soil bacteria to convert it into sulfuric acid, which lowers the pH over several months. Apply granular sulfur in conservative, split applications, generally not exceeding five pounds per 1,000 square feet in a single application. Attempting large pH adjustments too quickly can damage the turf, requiring patience as the soil chemistry changes over the growing season.
If the soil test confirms a phosphorus deficiency, apply a targeted starter fertilizer containing a higher middle number (P). Select a fertilizer with little to no nitrogen for the initial correction to avoid over-fertilizing this low-input grass. For environmental stress, ensure the lawn receives deep, infrequent watering to encourage strong root growth. Water the grass to deliver approximately one inch of water per week, allowing the soil to dry slightly between sessions.