Precautions With Ferrous Sulfate & Iron for Moss

Ferrous sulfate, also called iron sulfate, is often used to kill unwanted moss -- members of the Musci class. Unlike most common garden plants, mosses lack true vascular systems and roots. Iron-based moss killers work by desiccating moss. When using ferrous sulfate or other iron-based moss products, take precautions to time applications properly, protect surrounding areas, apply safely and prevent a mossy return.

The effectiveness of iron-based products against moss depends on timely applications. Mosses grow in every climate, from U.S. Department of Agriculture plant hardiness zones 1 through 13 and beyond. Apply ferrous sulfate and other iron-based products when moss is moist and actively growing. A cool day with no precipitation forecast for 48 hours or more is best. In most U.S. climates, late fall and early spring are the best seasons to apply iron-based moss killers. Take precautions to time applications properly, and mosses turn black and die within days. Leave them to decompose, or rake them away.

Applied in the recommended quantities, ferrous sulfate and other iron-based products target moss and leave surrounding grasses and plants unharmed. New grass can be iron-sensitive, so avoid newly planted lawns. These natural-based products have little effect on established plants. The iron in these products can permanently stain concrete, brick and stone. When using any type of iron-based product, stay away from sidewalks, patios, stone pathways and similar areas, unless you want them rusty red. If the product accidentally touches these surfaces, stop what you're doing and wash and clean the area immediately.

Most lawn grasses prefer soil pH in a slightly acidic range from 5.8 to 6.5, but using high-nitrogen turf fertilizers tends to lower soil pH over time. Because mosses prefer even more acidic soil, their presence may signal low soil pH. Sulfur in ferrous sulfate and similar products can lower pH even more. Take precautions and periodically test soil pH levels so your lawn stays in the grass-enhancing range. Low pH also limits the availability of nitrogen to plants. Many moss killers add nitrogen to offset acidity and stimulate grass growth in treated areas.

Follow the label instructions carefully for iron-based commercial moss products. To apply ferrous sulfate directly, mix 5 ounces of ferrous sulfate with 4 gallons of water in a lawn sprayer to treat 1,000 square feet. If you plan on reseeding, apply lime to deactivate iron, which can be toxic to seedlings. Once the moss dies, apply 5 to 10 pounds of ground limestone over the same treatment area. Whenever you're working with ferrous sulfate, lime or other lawn and garden products, take proper safety precautions. Wear protective clothing, including gloves and protective eyewear, and avoid chemical contact with exposed skin. Clear the area of people and pets, and wash thoroughly with soap and water afterward.

Mosses don't take over and force grasses out; they simply move in where grasses fail. After using ferrous sulfate and other moss-killing products, take measures to ensure the moss stays gone. Correct conditions to make your lawn more grass-friendly and less hospitable to moss. Lawn mosses prefer poor drainage, constant moisture, shady areas, scalped lawns and compacted soil -- the opposite of most lawn grass preferences. Improve drainage, avoid overwatering, aerate the soil, mow at proper heights and adjust the surroundings so sun streams in. Healthy, strong grasses keep mosses away.