Is Iron Sulfate Safe for Home Gardens?

Garden Application

• Iron sulfate is used to supply iron in deficient soils as well as to lower the pH of soils to suit the needs of acid-living plants. It is a safe and nontoxic fertilizer and soil amendment when used in this context. But applying it as a source of iron in situations where lowering the pH is not needed can yield disastrous results. Thus, it is important to know the pH of your soil, as well as the pH requirements of the plants you are working with before applying iron sulfate. A soil test provided by the local cooperative extension service can determine the pH value of your soil, though simple pH test kits are available at most well-stocked garden centers.

Iron Sulfate in Excess

• Iron sulfate can acidify the soil to a degree that is inhospitable to any plants if applied in excess. An excess of iron can also limit the availability of manganese, zinc, phosphorus in the soil. This is unlikely if the application rates suggested on the package are followed, but only a soil test can confirm the exact quantity to apply in a given location. Care should also be taken to prevent iron sulfate from entering waterways. The iron can put delicate aquatic ecosystems out of balance and the acidification of water can be fatal to fish. Do not apply iron sulfate in areas immediately adjacent to waterways.

Personal Precautions

• Iron sulfate is derived from naturally occurring minerals and if used correctly does not pose a significant threat to humans, pets or wildlife. But it is a granular product that produces dust when applied, so take care not to inhale it. There is not a huge cloud of dust when using the product, so inhalation is unlikely as long as it is applied at arm’s length. A dust mask is a good precautionary measure when working with iron sulfate on windy days, however. Wear rubber gloves when applying iron sulfate -- the material has an unpleasant odor and causes dryness and itchiness where it contacts the skin. Iron sulfate can cause serious health hazards if ingested, so always take common sense precautions like storing the product out of the reach of children.

Staining

• One of the greatest dangers of iron sulfate is not a health risk but a cosmetic issue. Most materials are stained a rusty brown color on contact with the product. This includes concrete surfaces, lawn furniture, cars, clothing and skin. This fades quickly on some surfaces, but concrete in particular holds the color indefinitely, much to the chagrin of unsuspecting gardeners. In fact, iron sulfate is intentionally used by masons as a nontoxic concrete stain.