Genetic and Soil Causes of Color Variation in Kentucky Bluegrass

Beyond Nutrient Deficiency

Same Denver scenario as previous article, but this expert (JHG) offered additional explanations beyond iron.

Genetic Differences Between Old and New Grass

• Modern patented cultivars bred for darker color, disease resistance, etc.
• Old lawn may be common-type or older variety with lighter genetic color.
• Even with identical care, genetic color potential differs.

Diagnostic Test: Nitrate Starvation

• Stop fertilizing until entire lawn shows minimum color (nitrogen starvation).
• Then apply high-nitrogen fertilizer uniformly.
• Observe green-up uniformity. Persistent differences = genetic or soil variability.

Soil Variability Factors

• Localized drainage differences.
• Compaction variations.
• Organic matter pockets.
• Previous treatment history (spills, pet spots, etc.).

Remediation Approaches

• Iron supplementation: Helps both genetic and soil-related pale color.
• Top-dress problem areas: Compost/potting soil to improve root zone.
• Equalize water/sun: Ensure uniform irrigation and pruning.
• Consider alternative grass: Tall Fescue cultivars (SR-8600, Rembrandt) more consistent in Colorado transition zone.

CSU Reference

Colorado State University campus grounds use improved varieties—observe their selections for local adaptation.