Iron and Turfgrass

Iron is considered a micronutrient for turfgrass. Iron is a key component of proteins and plant enzymes involved in nitrogen metabolism, plant respiration and chlorophyll synthesis. Due to its role in the chlorophyll synthesis process, iron level can impact turf color in many situations.

Turfgrass will absorb iron via the roots. The iron will be in a stable, reacted form – examples are shown below. Each source has a different iron content and a different availability to the turf via water solubility.

  • Ferric Sulfate
  • Ferrous Sulfate
  • Iron Sucrate
  • Ferric Oxide
  • Ferrous Oxide
  • Chelated iron
  • Organically derived iron

The words “ferrous” and “ferric” designate the oxidation state of the iron atom – ferrous referring to Fe++, which is relatively soluble in water and ferric referring to Fe+++, which is only somewhat water-soluble and only in acidic environments (pH of 6 or less). Iron oxide typically contains both ferric oxide and ferrous oxide. Iron sucrate is iron oxide combined with sugars to reduce staining risk (discussed later). Chelated iron features iron paired with a chelating agent that can be spray applied. It is easily absorbed by the turf. Organically derived iron refers to the iron present in sources such as biosolids and compost – normally at a very low percentage.

For turfgrass, the generally accepted target range for iron level in soils is 30 – 100 ppm. Turf deficient in iron suffers from “chlorosis” – identified by a pale green overall color. Usually the reason for chlorosis is that the iron in the soil is not available to the plant – especially in alkaline soil conditions. If the soil pH can be adjusted down to 6.0 or so, the iron in the soil will become available and the turf color should gradually improve.    

Some turf fertilizers have an iron content of 1 – 3% from iron oxide. The intention of this fertilizer formula feature is to supplement the iron level resident in the soil. This is an economical benefit, but the iron content is derived primarily from ferrous oxide – so the soil pH needs to be 6.0 or below to see an effect. Any visual effect (such as a deeper green color) will also be minor and slow – perhaps several weeks.

When applying granular iron compounds to the soil, be aware of the risk of staining on flat surfaces – particularly light colored concrete. If the iron particles are crushed on the concrete (by tires, human shoes, or even heavy sweeping), rust colored stains will appear that can be found objectionable and difficult to remove. Iron products based on oxide or sulfate are known for this undesirable property. Particles landing on susceptable surfaces should be lightly swept or blown into the turf. Iron sucrate can be used as an alternative to reduce the risk, but particles should still be removed.

As with any turf care product, read and follow the Directions for Use provided by the product labeling.