About Colorado cracked lichen (Acarospora coloradiana H. Magn.)

Colorado cracked lichen is a small, vibrant, crustose lichen found in the southwestern United States and parts of Mexico. It grows in alpine meadows, high-ridge areas, and on rocky outcrops. While often mistaken for "cracked lichen" due to its pale appearance, it is actually a microscopic, moss-like plant that grows in dense clusters. It is highly prized by landscape architects as it provides a textured, earthy surface that mimics the native terrain without being toxic to most mammals.

Growing Conditions

USDA Zone: Ideal for zones 5 through 8.
Sunlight: Thrives in full sun (full or partial shade is generally acceptable).
Soil: Requires well-draining, neutral to slightly acidic soil. It prefers loose, compacted earth. Avoid planting on wet, saturated ground.
Water Needs: Moderate. It likes slightly moist but well-draining soil. Water is best applied when the top 4 inches of soil feel dry.
Mature Size: Typically grows to a height of 4 to 10 inches. These clusters are dense, forming a compact mat that can be a natural ground cover for ditches or erosion control.

Planting Guide

Timing: Plant in late winter or early spring before the ground freezes, or immediately after the last snowfall has melted to avoid damaging seedlings.
Spacing: Space each cluster 8–12 inches apart. The lichen prefers a loose, clumping growth habit; dense planting can lead to overcrowding and rot.
Establishment Care: Water the plants deeply once established, but avoid wetting the undersides of leaflets, as this encourages fungal decay. Monitor for pests and diseases closely; if leaves turn yellow or die back, it may indicate an early infection.

Seasonal Care

Spring: Begin by establishing the clumps by water-soaking soil and lightly troweling to loosen it. This allows new growth to emerge before the summer heat and drought stress.
Summer: Reduce watering frequency as soil dries. Monitor closely for pests like aphids or spider mites. If leaflets become necrotic, remove dead tissue to prevent spreading pathogens.
Fall: Consider applying a mulch layer (straw or bark) around the base to suppress weeds and retain moisture. Ensure the soil remains slightly acidic; lime can be added as needed.
Winter: Do not dig up dead clumps that are dead. If any survive, water them thoroughly to encourage dormancy. Do not cover them with soil, as this can kill the plant. In Southern states, ensure that the soil is well-drained to prevent root rot during this period.

Common Problems

Throat Myths: While often called "cracked lichen," Acarospora coloradiana is harmless to humans.
Fungal Infections: Infection of leaflets can occur via contact or airborne spores. Treat by removing infected tissue and replacing it with healthy seedlings.
Bacterial Wilt: Insect pests such as aphids can transmit bacteria to leaflets. Remove infected leaves and inspect the area for fungal growth.
Root Rot: Overcrowded soil or poor drainage can lead to this.

Companion Plants

These plants help suppress weeds and reduce competition for sunlight and water around your lichen clumps:

Duckweed: Grows rapidly in slow water, competing effectively with lichen mats for moisture.
Black Walnut: Produces thick bark and a strong scent that repels many herbivores and weeds.
Barnyard Grass (Phragmopoides): Its dense foliage shades the area well and is highly effective at controlling grass growth near the edge of the lichen.

Pro Tips for Professional Landscapers

Mulch Management: Professional landscapers often recommend using organic mulch (like shredded leaves) around the base of every lichen cluster. This not only retains moisture for the lichen but also protects it from frost. However, avoid covering the entire plant mass; the lichen can tolerate direct sunlight when it emerges from the ground.
Seeding Quality: When using lichen as a seed source, ensure the seeds are from a high-quality source. Low-quality seeds are difficult to germinate in the cold soil of Southern states and can lead to poor establishment.