Moss can quickly take over a lawn in July, but a simple method using ferrous sulphate (iron sulphate) kills it and prevents regrowth without harming grass, according to BBC Garden Rescue presenter Lee Burkhill, known online as the Garden Ninja.
Moss thrives in July due to rainy weather and frequent watering. While some gardeners tolerate its fairy-tale appearance, moss kills grass by blocking sunlight and absorbing soil nutrients, leaving lawns thin and parched. Burkhill shared his advice to combat this.
Why Ferrous Sulphate Works
Burkhill explained: “Moss killers typically contain ferrous sulphate (iron sulphate), which is highly effective at killing moss whilst also providing iron that grass loves. You can buy moss killer as either a granular or a liquid product. Both work well, though I find granules easier to apply evenly across larger lawns.”
Moss is highly sensitive to iron, which disrupts its cells and causes rapid dehydration, turning it brown and dead. Grass, however, benefits from iron as it aids chlorophyll production, resulting in a lush green colour. Ferrous sulphate also creates an environment less favourable for moss regrowth.
Application Tips for Summer
To apply, check the weather forecast first. Avoid treating lawns during a heatwave or on hot days, as grass is already stressed. Ferrous sulphate works best when soil is moist, so apply the day after rain when it is cool and cloudy.
Remove debris from the lawn, then mix ferrous sulphate with water according to package instructions. Keep the solution away from patios, driveways, or paving, as it can stain stone. For patio moss, a baking soda solution is recommended instead.
Results and Aftercare
After seven to 14 days, moss will turn brown and die, making it easy to remove by hand. Burkhill noted that moss only grows on weakened grass, which is common in summer. Ferrous sulphate does not fix underlying issues, so he advises aerating and scarifying the lawn before summer ends to improve grass health and prevent moss from returning.
