Foliar Iron Application

Foliar Iron Application

Note : the article below was written by fellow lawn care enthusiast MorpheusPA and is being reproduced here with his permission. Head on over to his blog for more great tips on lawn and garden care : The Green, Green Grass of Home

Iron applications help with the lawn color, but generally do little for the soil.  They’re always optional, but if you find your lawn color is more yellow than you like, they will help restore color.

There are three methods–bottled iron products from any big box store, ferrous sulfate, and ferrous ammonium sulfate.  This article discusses all three below.

Warning:  Iron should never be applied if the temperature will exceed 85 within the next 24 hours.  If the weather takes you by surprise, irrigate the grass enough to wash the iron off of the leaves.  Failing to do so may risk a burn.

Bottled Iron Products:

Almost every big box and local gardening store will carry pre-mixed bottles of iron.  Often, the iron is listed as “chelated,” or bound to an organic molecule to preserve it against chemical reaction.  While this isn’t important when the product is on the leaves, it will help the grass continue to absorb the iron after the product has been watered in.

Most bottled iron products contain 3% to 6% iron by weight, although there are certainly exceptions.  Check the label to make certain that the product’s price is reasonable for the amount of iron it contains.

Simply follow the label instructions and observe all warnings about temperature of application.  If the temperature limit of usage is not listed, assume it shouldn’t be used if temperatures exceed 85.

Most of the chelates used aren’t effective at higher pH levels, so there isn’t much sense in paying for the chelation if your pH is much over 7.2.

These products are readily available, pre-mixed, and sometimes come in their own spray containers.  The down-side is that they tend to be much more expensive than home-made options.  They’re a great initial test to see if your lawn will respond well to iron, and a good option even after that for people who don’t wish to mix their own.

Ferrous Sulfate:

Ferrous Sulphate

The name sounds a bit scary, but it’s just iron sulfate, or iron bound to sulfur and oxygen. Ferrous sulfate (technically, ferrous sulfate heptahydrate, or including 7 molecules of water attached to the ferrous sulfate) is 15% elemental iron by weight, or one of the higher amounts of iron easily available to homeowners and safe for lawns.

Ferrous sulfate, or iron sulfate, is often available in small quantities at gardening stores in the Bonide brand, and the quality is excellent. Larger quantities can be purchased online.

For elite bluegrasses, 4 ounces of ferrous sulfate per thousand square feet diluted in a minimum of 1 gallon of water seems to be the best amount to use.  For non-elite bluegrasses, any amount up to and including 4 ounces of ferrous sulfate in 1 gallon of water per thousand square feet seems best.  For fescues and ryegrasses, 2 ounces per thousand in 1 gallon of water per thousand square feet maximum would be the limit.  Overapplication will result in very dark grass.  In the case of fescues and ryegrasses, it can turn an unnatural almost black-gray-green color that’s fairly unattractive.  The grass is healthy, and will eventually regain normal coloration, but this can take several weeks to months.

Mix externally in a bucket and pour the solution into the sprayer, leaving any undissolved ferrous sulfate and foreign material behind.  This will reduce clogging considerably.

Mix the above amount of ferrous sulfate plus a small amount of any surfactant into 1 gallon of water.  For a surfactant, you can use a quarter to half an ounce of baby shampoo or inexpensive adult shampoo, dish soap (non anti-bacterial), or Morpheus Soil Conditioner.

Again, never spray the lawn if the temperature will exceed 85 degrees within 24 hours.  If you discover that the weather has changed and the temperature is now too warm, irrigate the lawn immediately to wash the mix off the leaves and into the soil.

Discard any unused solution appropriately as it doesn’t store well and will rapidly turn to rust.  Make certain to clean your sprayer afterward, including running water through the wand, to avoid clogs.

Ferrous Ammonium Sulfate:

Ammonium Sulphate
Ammonium Sulphate

This name sounds a bit scarier than ferrous sulfate!  However, it’s simply iron and ammonia bound to a sulfate.  Although it contains less iron by weight than ferrous sulfate, the mix is home-made and will contain the same amount of elemental iron as the ferrous sulfate you put into it.  Consequently, if you used 4 ounces of ferrous sulfate, you’ve applied 0.60 ounces of elemental iron.

So why use it?  The darkening from ferrous ammonium sulfate exceeds that of ferrous sulfate.  Ferrous ammonium sulfate is a somewhat more stable solution as well, being less likely to turn to rust before the grass can absorb it. Ammonium sulfate contains 21% nitrogen, supplying the nitrogen needed to generate chlorophyll (the green color) in plants.

Making ferrous ammonium sulfate requires two chemicals:  ferrous sulfate and ammonium sulfate.

Ferrous sulfate, or iron sulfate, is often available in small quantities at gardening stores in the Bonide brand, and the quality is excellent. Larger quantities can be purchased online.

Ammonium sulfate is often not available at local stores, but can be purchased online from The Organic Store.  The link is to the main fertilizer section, so you will need to scan down to find ammonium sulfate.

For elite bluegrasses, 4 ounces of ferrous sulfate per thousand square feet diluted in a minimum of 1 gallon of water seems to be the best amount to use.  For non-elite bluegrasses, any amount up to and including 4 ounces of ferrous sulfate in 1 gallon of water per thousand square feet seems best.  For fescues and ryegrasses, 2 ounces per thousand in 1 gallon of water per thousand square feet maximum would be the limit.  Overapplication will result in very dark grass.  In the case of fescues and ryegrasses, it can turn an unnatural almost black-gray-green color that’s fairly unattractive.  The grass is healthy, and will eventually regain normal coloration, but this can take several weeks to months.

To create ferrous ammonium sulfate, take the amount you chose above and multiply by 0.85.  Add that much ammonium sulfate to the mix.

So for several mixing levels:

Ferrous sulfate amount: Ammonium sulfate amount:
1.0 oz 0.85 oz
2.0 oz 1.70 oz
3.0 oz 2.55 oz
4.0 oz 3.40 oz

 

…and so on, always using 0.85 ounces of ammonium sulfate for each ounce of ferrous sulfate you use.

What happens if you make a slight mistake?  Nothing, really.  Using too much ferrous sulfate is no issue at all, you’re simply applying a mixed solution of ferrous sulfate and ferrous ammonium sulfate.

Using too much ammonium sulfate is not much greater of an issue.  Although ammonium sulfate can strip a bit of calcium from the plant, a minor imbalance in the amount used won’t cause any problems.  Some fertilizers use ammonium sulfate as their primary nitrogen source and work well without damaging the grass.

Mix externally in a bucket and pour the solution into the sprayer, leaving any undissolved ferrous sulfate, ammonium sulfate, and foreign material behind.  This will reduce clogging considerably.  When adding it to your sprayer, use a small amount of any surfactant into 1 gallon of water.  For a surfactant, you can use a quarter to half an ounce of baby shampoo or inexpensive adult shampoo, dish soap (non anti-bacterial), or Morpheus Soil Conditioner.

For this chemical, spraying above 80 degrees is not recommended as it has a higher probability to cause burning.

If you discover that the weather has changed and the temperature is now too warm, irrigate the lawn immediately to wash the mix off the leaves and into the soil.

Discard any unused solution appropriately as it doesn’t store well and will rapidly turn to rust–although more stable, it will still transform over a day or so.  Make certain to clean your sprayer afterward, including running water through the wand, to avoid clogs.

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