Iron / Ferrous Sulfate Heptahydrate – Iron for a green lawn


Hello, I live near downtown Toronto, so my front and rear yards are very small – each under 700 sq ft. I am not lawn care savy and don’t know how to care for my lawn. All I do is mow & rake. I let the rain water my lawn. I read that to get a deep green colour, I should use iron. Scotts Green Max is 27-0-2 with 5% Iron – – and Canadian Tire GolfGreen NitroGrow is 34-0-12 with either 2% or 4% – their website isn’t clear – . sells Ironite 1-0-1 with 20% Iron, but is no longer sold in Canada – . Can I use Ferrous Sulfate Heptahydrate – ? Do you know how much powder to mix with how much water and what area it will cover to get 20% iron? Or should I apply a lower percentage? Thanks.


There are a couple of reasons to apply iron to a lawn – to correct an iron deficiency, or  simply to achieve a greener lawn.  From your note, it seems that you are keen that your lawn remain healthy, but also would like the lawn to look greener.

Several nutrients are essential for a lawn to remain healthy.  This includes iron, a micronutrient that helps grass produce chlorophyll, which is needed in photosynthesis.  Chlorophyll is green in colour, and when grass is deficient in chlorophyll (this is called chlorosis), its blades turn yellow or sometimes nearly white.  Most soils should have enough iron present to meet the needs of the lawn, so a supplement is not needed.

However, if you feel the soil is iron-deficient, the first issue to determine would be whether the soil pH is too high (too alkaline).  If this is the case, then soluble iron fertilizers would help provide iron in a form that plants can absorb.  The best time to apply iron would be in the spring.  However, in the long-term, the best solution for iron deficiency would be to correct the soil pH.

Here are some steps to consider in keeping your lawn healthy:

This includes

  • Nourish the soil. Use compost during the growing season and apply fertilizers in late summer/early autumn. Balanced/complete fertilizers contain several nutrients, including iron.
  • When you mow the grass, leave the clippings on the lawn – don’t remove them.
  • Aerate the lawn to prevent compaction of the soil and permit more water and air to penetrate.
  • Overseed in the spring and fall to avoid growth of weeds.
  • Ensure the lawn gets enough water. If rain does not suffice, the lawn should be watered deeply once a week.

However, although a lawn may be healthy, iron fertilizer is applied by some to enhance the green colour of the lawn.  See Penn State Extension. Turfgrass fertilization.   Search for “iron” and towards the end of this document you will see a section that discusses the iron salts that may be used and how these are applied. You’ll see that the rate/amount of iron fertilizer used for grass varies depending on the type of iron used (different iron salts will have different iron concentrations), the time of year (if applied when grass is growing quickly, the enhanced green colour may last for just 2-3 weeks, while applications during slow growth periods may last for a few months) and number of applications.   See also University of Arizona Cooperative Extension. Iron applications for turf.  Note that if too much iron is applied, it can turn the grass a greyish colour and could be harmful.  As well, iron can stain hard surfaces like driveways, paths or decks.

It is not permitted for us to recommend any particular product to use. I suggest that you check Landscape Ontario  and contact a lawn care expert to determine if an iron-containing product would be recommended for your lawn, and if so, which iron product should be used and at what concentration.