Lawn Health
Lawn Fungus Explained (and How to Keep It in Check)
Fungus is a normal part of healthy soil — until heat, humidity, and excess nitrogen let it explode. Here's what fungus does, the warning signs, and how to control it in summer.
May 15, 2026 · 4 min read
Fungus has a bad reputation, but it’s actually a vital part of healthy soil. The trick is keeping it balanced.
What fungus does for your lawn
Fungi are living organisms that feed on dead material, helping to decompose it. In your lawn, fungi break down the clippings from mowing — and as that material vanishes into the soil, it becomes nutrition for future plant life.
In other words: the more fertile your soil, the healthier your turf — and fungi are part of what makes soil fertile.
When fungus becomes a problem
Heat and fungus conditions combine to stress a lawn, and can even damage it. The visible warning signs:
- Mushrooms popping up in the lawn
- “Dog vomit” fungus — a slimy growth that signals fungus is active
During hot weather (think August), humidity, and excess nitrogen, fungi populations get out of control. Their life cycle — from baby to adulthood to reproduction by the millions — can be as short as 18 hours. In winter, cold weather slows that cycle way down.
The two things fungus needs
Fungus requires two things to run wild:
- Excess water
- Excess nitrogen
We can’t avoid watering during the summer — the lawn needs it. But we can avoid the excess nitrogen.
How to keep it in check
- Do not apply nitrogen fertilizer during the warm summer months. This is the single biggest lever you control. (See our fertilizing guide →)
- Apply Ferrous Sulfate instead to keep color without feeding fungus.
- Aerate the lawn during summer to improve airflow and reduce the damp conditions fungus loves.
Manage water and nitrogen wisely, and fungus stays the helpful soil partner it’s meant to be.
Frequently asked questions
- Is lawn fungus bad?
- Some fungus is actually good — fungi decompose grass clippings and dead material into nutrients that feed your lawn. The problem is when heat, moisture, and excess nitrogen let fungus populations explode and stress the grass.
- What are signs of fungus in my lawn?
- Mushrooms and a slimy growth often called 'dog vomit' fungus are signs that fungus is active in your soil.
- How do I control lawn fungus in summer?
- You can't avoid watering in summer, but you can avoid the other trigger: excess nitrogen. Don't apply nitrogen fertilizer in hot months — use Ferrous Sulfate instead, and aerate the lawn to improve airflow.