Iron is needed by grass in smaller amounts than nitrogen, phosphorus, and potassium, but it’s still a critical growth component. Regularly adding iron to your lawn during the spring, summer, and fall can help keep it green and lush. Iron lawn supplements are available in liquid and granular form and can be applied every two to four weeks in most cases.
How do I know if my lawn needs iron?
Iron deficiency, also known as iron chlorosis, typically gives your lawn a yellowish, mottled appearance. The deficiency shows in this manner because iron is a chlorophyll component, making the grass look green.
Symptoms initially show as a light green cast across the uppermost part of your lawn while the lower blades stay a darker green. As the deficiency worsens, the yellowing spreads to the entire leaf blade. In severe cases, the upper leaves can turn white, or the veins in the grass blades may appear dark green with pale yellow between them.
To confirm an iron deficiency in your soil, it’s best to take a soil sample and have it professionally tested for iron concentration. While you’re at it, you can have the lab analyze nitrogen, phosphorus, and potassium too. The soil test report can offer insight on your soil’s fertility and may recommend fertilizer rates tailor to your yard, including how much iron you need to add.
Pro tip: In many cases, you can have soil testing done through your local cooperative extension office. A cooperative extension is a program within a land-grant university that helps the community with issues related to gardening and agriculture. You can use this list of cooperative extensions nationwide to find your nearest office.
When to apply iron to your lawn
Iron supplements can be applied to your lawn, whether cool-season or warm-season turfgrass, throughout the growing season. As long as your grass is actively growing, it’s okay to give it a boost of iron to help it green up.
However, it’s best to avoid foliar-applied liquids and stick to granular products during the summer when the sun is blazing and temperatures are soaring. Granular iron products will help prevent your grass from burning.
Spring
Once early season temperatures are 60 to 70 degrees Fahrenheit, an iron application can help your lawn green up. You can also apply iron after scarification — a process that removes moss and thatch — to help your grass recover.
- Early spring: Apply iron as the turf begins to green up after winter dormancy to enhance its color and overall health.
- Late spring: Apply iron before the onset of summer stress to help the grass maintain its vigor and color.
Summer
Warmer temperatures and intense sunlight in the summer often stress your lawn, giving it a slightly lighter green appearance. A mid-summer application of a slow-release, granular iron product can help keep it green, especially with cool-season grasses like Kentucky bluegrass and perennial ryegrass that usually go dormant during the hottest parts of the year.
Fall
When the weather cools, you can change to applying liquid or granular iron to your lawn.
- Early fall: Apply iron after the heat of summer has subsided to help the turf recover and prepare for winter.
- Late fall: Apply iron just before the grass goes dormant to enhance its color going into winter and boost early spring green-up.
The different types of iron products
Iron lawn additives come in two forms: as liquid or granules.
- Liquid applications can be diluted and sprayed onto the grass, where they are absorbed through the blades and begin to work almost immediately. Liquid iron products typically cost between $20 and $50 for 32 ounces.
- Granular products can be spread across the lawn and take effect once watered into the soil. These applications don’t work as quickly but may last longer, so you need fewer treatments for a green, healthy lawn. This type of iron costs approximately $25 for a 15-pound bag.
These products are often “chelated,” where an organic compound is added to keep the iron soluble and more easily absorbed by the grass roots. The organic molecule has multiple binding sites that “claw” onto the metal iron ion, helping to stabilize it and keep it available for plant uptake.
What causes iron chlorosis?
Turfgrass may experience iron chlorosis because the soil is iron-deficient, or soil conditions like high pH or compaction make the iron unavailable for plant uptake.
Chlorotic grass fades from its usual beautiful green to a yellowish color because iron is needed to make chlorophyll, the pigment that gives grass its green color. Without chlorophyll, the grass can’t continue to photosynthesize, eventually leading to poor strength and vigor.
Tips for applying iron to your lawn
- Run a soil test before applying iron to make sure you have an iron deficiency.
- Check the soil pH to see if it’s in the recommended range between 6.0 and 7.0 for lawns. Adding extra iron doesn’t do much good if the pH is out of this range, as it quickly becomes unavailable in the soil. You’ll need to adjust the soil pH before adding iron.
- Before applying iron, make sure your lawn is getting enough water and macronutrients like nitrogen, phosphorus, and potassium.
- Avoid applying iron during hot weather.
- Follow the package instructions to prevent overapplying.
- Some experts recommend applying iron after mowing because the freshly cut grass allows for better contact between the iron and the soil.
- Apply granular products to damp lawns and water them well to activate and move them into the soil.
- Apply iron products evenly to avoid creating dark and lighter green stripes on your lawn.
FAQs about adding iron to your lawn
How long does iron application last?
With most iron applications, label recommendations state you can reapply after two to four weeks. This quick reapplication schedule is possible because iron rapidly binds with other nutrients once in the soil — especially in alkaline soils — and becomes unavailable for plant uptake.
Is yellow grass always an iron deficiency?
A yellow lawn doesn’t always indicate a problem with iron; it can also signify a nitrogen deficiency. A key to determining which nutrient is lacking is where the symptoms are showing up on the plant. Nitrogen is mobile within the plant, while iron isn’t, which means your grass will move nitrogen from older tissues to newer tissues to meet its needs. It can’t do this with iron.
Because of the differences in mobility, you’ll see nitrogen deficiency in old growth and iron chlorosis in new growth. If the lowermost, older leaves turn pale green or yellowish-green, it’s likely a nitrogen deficiency. Iron chlorosis is likely if the uppermost, newer leaves turn pale or yellowish-green.
How much iron should I apply to my lawn?
Running a soil test that checks soil pH and iron concentration is helpful in calculating application rates. Once you know those two parameters, you can determine how much iron to add.
The University of Arizona Cooperative Extension recommends applying 2 to 4 ounces of product per 1,000 square feet of lawn to fix iron chlorosis.
Need a hand with lawn care?
No one wants to stand on their back steps and look out across their lawn to see a yellow-green hue where they want to see a lush green expanse. If you’re trying to figure out the problem and feeling overwhelmed by soil testing, adding amendments to adjust the pH, and applying iron (or other fertilizer to correct nutrient deficiencies), turn to the pros.
Lawn Love will connect you with a local lawn care expert who will work diligently to give you a lush, green lawn so you don’t have to lift a finger.
Main Image Credit: Jerry Norbury | Flickr | CC BY-ND 2.0
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