When to Apply Iron to Lawn

When to Apply Iron to Your Lawn for Best Results

Iron application can help make your lawn greener and healthier. If you’ve noticed that your lawn’s color is a lighter green or even bordering on yellow, it’s possible that your soil has an iron deficiency. Properly adding iron to your lawn requires careful application and timing. Knowing when to apply iron to lawn areas will get you the best results to keep a green lawn all summer. That said, applying Iron at the wrong time can do more harm than good.

Today I’ll explain what you need to know about the timing of Iron applications to your yard to get that rich, deep green color you want for your grass.

Let’s get started with some basics.

Trust and Accuracy Information

This article was last updated on by Lawn Chick Owner Sarah Jameson
Article content reviewed for accuracy by Horticulturist Arthur Davidson, A.S.

Why is Iron Important for Your Lawn?

Iron supplements for lawns became especially popular with homeowners trying to rival the lovely green grass of golf courses.

It’s especially effective when you apply iron to Kentucky Bluegrass or Fescue Grass lawns. It can help these types of grasses retain a dark green shade during the hottest parts of the summer.

Why Apply Iron to Lawns?

Iron also doesn’t cause extra growth or create a need for additional irrigation, which nitrogen fertilizers do. If you’d like to learn more about the difference between Nitrogen and Iron applications, start here.

When Should You Apply Iron Supplements to Your Lawn?

The general rule is that you should use iron supplements on your lawn in the spring. Of course you can apply iron supplements at almost any time of year, but iron will deliver the best results when applied to your lawn when air temperatures are between 40 and 80 degrees Fahrenheit. The ideal air temperature is in the 60s or 70s. This is why Iron application during the heat of summer may not be as effective or deliver the desired results — it’s too warm out.

Always remember to read the instructions to make sure you are using the supplement properly. Remember that you want to avoid overdoing your lawn with iron.

Apply Iron Only As Needed

Grass usually doesn’t need a large amount of iron. In fact, it’s usually only beneficial to apply extra iron if you have a soil test indicating iron deficiency.

Don’t automatically assume an iron deficiency is the cause of your lawn yellowing or being light in color.

Iron Application Schedule for Lawns - When to Apply Iron for Best Results?

First, ensure that it’s sufficiently watered and has all other major nutrients. If those don’t work, you can consider using iron supplements, but your best way to know for sure what your lawn is lacking and how to improve performance is to perform a soil test. This is the one I use. I order it from Amazon every spring and let those results guide me in applying the right products (and not wasting money on things my lawn doesn’t need) each year.

Best Overall Lawn Soil Test Kit

The Soil Test Kit I Use & Recommend

There are many options for testing your lawn’s soil, but I prefer a lab-based soil test that provides a detailed analysis of your soil’s nutrients and what’s needed for your lawn to thrive.

I use this one from MySoil every year.

And if you’re interested in taking the guesswork out of what to do next after you get your soil test results, consider Sunday’s subscription lawn-care plan. They test your soil for you and use local weather data to send you exactly what your lawn needs, when it needs it. It’s pretty fool-proof – you can Click Here for Your Instant Lawn Analysis and take 15% off your order with promo code LAWNCHICK2024.

Two Kinds of Iron Supplements for Your Lawn

Iron fertilizers are found in multiple varieites, but they can be grouped into two main categories:

  • Organic Iron Fertilizers
  • Synthetic Iron Fertilizers

Organic Iron Fertilizer Products

Organic iron fertilizer is comprised of organic iron sources, such as those found in Greensand and Milorganite. These break down more slowly but are healthier for your lawn in the long term. The iron in them also has natural chelation, which makes it easier for your grass to absorb.

With organic iron fertilizer, you won’t have to worry about your concrete getting stained either. Also, these organic fertilizer products with Iron tend to contain other ingredients that help make your lawn healthier.

Synthetic Iron Fertilizer Products

Synthetic iron fertilizers tend to be inexpensive and act quickly to improve your lawn. Sometimes these will need to be sprayed on your lawn, but many of these products are available in granule form.

If you go overboard with synthetic fertilizer products with Iron you could end up with grass that turns gray (yes, really). Also, synthetic iron fertilizers can leave stains on concrete.

Be careful while applying this kind of product so you do not over-apply or spill it on your concrete driveway or walkways.

Two Forms of Iron Supplement for Your Lawn

Iron supplements for your lawn generally come in two different forms:

  • Spray / Liquid
  • Granular

Iron in Spray Form

Using liquid iron in a spray form facilitates foliar feeding. This kind of feeding tends to have a more efficient and expedient effect on your lawn (you’ll see results quickly).

When to Apply Liquid Iron to Lawn

You can put the iron directly on the blades of your grass. This means that it will get into the plant’s system more quickly. This kind of treatment will last between 3 and 4 weeks.

Products like spray-on Ironite and LawnStar Chelated Liquid Iron (the liquid Iron product I use, here’s the Amazon link) act quickly and can be useful to improve your lawn’s health and appearance.

Remember to be moderate in how you apply this. If you put on too much, you may end up with a gray lawn instead of the deep green color you’re after.

Iron in Granular Form

Apply granular iron supplements directly on the lawn soil with a broadcast fertilizer spreader or drop spreader. This type of iron supplement for lawns will take longer to have an effect since the structure of its molecules needs to be broken down, which happens over time.

When to Apply Granular Iron to Lawn

You won’t have to use this kind of iron supplement as often as you would a spray form, though, and the effect on the color of your grass tends to be more enduring.

What to Watch Out For When Applying Iron

It’s important to be aware that iron can stain concrete, and therefore you should be careful to avoid walkways, athletic courts, and concrete driveways when applying iron to your lawn.

This happens because of the chemicals in some synthetic iron supplements.

Iron can leave ugly orange stains (think rust stains) on your concrete patios and other hardscape features of your landscape, so this is something that you will want to keep in mind.

I use a supplement called Dr. Iron (Amazon link) which delivers great results and does not stain concrete, and I highly recommend it, especially if you’re concerned about preserving the beauty of your hardscape features. It works wonderfully to green up my lawn.

Avoid Summer Application to Stretch Your Dollar

Iron may be useful in making your lawn a deeper green color so it really pops in your neighborhood.

When to Use Iron on Lawn

And while it’s tempting to throw down Iron supplements early and often, you should apply it when air temperatures are below 80 degrees Fahrenheit to get the best results. Apply in the heat of summer and your supplement will be less effective since your grass won’t be able to absorb it quite as effectively.

Whenever you choose to apply Iron, it’s important to read and follow the manufacturer’s recommendation about coverage and application rate. Use one of these online tools to measure your lawn size to get your application just right.

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Additional Resources


Sarah Jameson’s blog, Lawn Chick, is read by over 2 million homeowners each year and she is regularly cited as an expert source of lawn care knowledge by major publications. Her goal is to meet you where you are, and help you achieve a yard you’ll be proud of. Ready to take the next step toward improving your lawn? Grab her free lawn care cheat-sheet: What to Do When - Take the Guesswork Out of Lawn Care, or upgrade your garage by browsing her favorite DIY lawn care products.

2 thoughts on “When to Apply Iron to Your Lawn for Best Results

  1. Robert Noble

    I am going overseed the lawn can i apply liquid iron with starter fertilizer? I will also be spraying tenacity for some weed issues. Ant thoughts on this concoction? Thanks.

    • Hey, Robert!

      You shouldn’t have any issue spraying the iron along with the starter fertilizer – just check to make sure there’s no iron in the fertilizer so you don’t go overboard. Too much iron and you’ll have a gray lawn (and lots of looks from the neighbors).

      If it were me I’d probably make sure I sprayed the Tenacity either a few weeks before or well after overseeding. It’s one herbicide that usually doesn’t bother turfgrass at all (which is why I love it), but seedlings can be finnicky, and I always try to avoid spraying any herbicides around seed or young grass just to make sure that investment in seed isn’t wasted.

      I also wonder what you’re planning to spray – if it’s something like Crabgrass that you want to clear out before overseeding, that can make sense (just do it well in advance so you can rake out the dead stuff and expose the soil for your new seed), but remember that crabgrass is an annual weed so everything you have now will die back on its own this winter anyway. A good pre-emergent application in the spring will stop most of the seeds it leaves behind from germinating next year. Not sure of your situation, but thought maybe that was worth mentioning!

      Good luck with your project – sounds like you’ve got a good combination of things planned for the fall. Hope it turns out great!

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