What is snow mold, and what can I do about it?
Snow mold (Latin: Microdochium nivale) is—contrary to what its name might suggest—not necessarily tied to frost or snow. The mushroom thrives especially in conditions of high humidity (e.g., dew or fog) and fluctuating temperatures between 0 and 8 °C.
If snow lies on unfrozen ground, this further promotes the growth of snow mold.
Factors that contribute to snow mold
Several factors can contribute to the growth of snow mold:
high humidity (dew, fog)
Alternating between low and mild temperatures
Snow on unfrozen ground
Intensive mechanical treatment of the lawn in the fall
High nitrogen applications in late fall
Potassium Deficiency
compacted soil
high pH level
Typical Symptoms of Damage
At first, small, watery-gray spots—about 5 cm in size—usually appear; these are also known as “wet rot.”
These spots can:
Enlarge to up to 25 cm
connect with one another
grow from the inside out
An active zone with brown to orange coloring is often visible at the edge of the affected area. The grasses often regrow from the center of the patches.
When humidity is high, a white-gray to pink, cotton-like fungal mycelium forms on the leaves.
What helps against snow mold?
The most important step is to avoid moisture as much as possible and to prepare the lawn well for winter:
Apply a low-nitrogen fertilizer in the fall
Apply a potassium-rich fertilizer in late fall
Regularly remove leaves, branches, clippings, and organic debris
Prevent waterlogging and reduce soil compaction
Do not subject the lawn to unnecessary heavy mechanical treatment in the fall
An Overview of Preventive Measures
The following measures can help effectively prevent snow mold:
Low nitrogen levels in the fall
Potassium Fertilizer in late fall
Reduce thatch (e.g., with turbogrün Lawn Aerator
light topdressing ( (Besanden)
Consistently remove leaves, branches, and pruning debris
No lime application in the fall
Scarifying in the Spring
longer drying periods between waterings
Keep the lawn as dry as possible overall