Milorganite vs Ironite: Which Is Right for Your Lawn?
Milorganite and Ironite are two of the most recognized specialty lawn products in the US, and they are frequently compared because both contain iron and both are used to improve lawn color. The comparison is somewhat misleading, because the two products serve different primary functions. Milorganite is an organic nitrogen fertilizer that also contains iron. Ironite is an iron supplement, not a fertilizer. Choosing between them depends on whether your lawn needs nitrogen, iron, or both.
What Milorganite Is
Milorganite is an organic nitrogen fertilizer produced by Milwaukee Metropolitan Sewerage District from heat-treated, dried biosolids. It has an NPK of 6-4-0 with approximately 2.5% iron. The nitrogen in Milorganite is organic and slow-release, delivered through microbial decomposition in the soil.
What Milorganite does:
- Supplies nitrogen (slow-release organic form)
- Supplies phosphorus (useful for lawn establishment, less relevant for established turf)
- Supplies iron for chlorophyll production
- Builds soil biology through the organic matter it delivers to the soil
- Is safe for all grass types and carries essentially no burn risk
What Milorganite does not do:
- It is not a high-iron supplement. At 2.5% iron, the iron content is meaningful but is not the primary value proposition of the product.
- It does not work as fast as synthetic nitrogen, the organic release is tied to soil temperature and microbial activity.
Full timing and use guidance is in when to use Milorganite on your lawn.
What Ironite Is
Ironite is a mineral supplement, not a fertilizer in the conventional NPK sense. Scotts Ironite Mineral Supplement 1-0-1 contains 20% total iron, 1% nitrogen, and 1% potassium. Its primary function is to supply iron to lawns that are iron-deficient, producing a greening response without the nitrogen surge that a standard fertilizer would cause.
What Ironite does:
- Supplies iron to correct iron chlorosis (interveinal yellowing)
- Provides a quick greening response when iron deficiency is the cause of discoloration
- Can be applied without triggering a growth surge, making it useful during summer when high nitrogen is undesirable
What Ironite does not do:
- It is not a substitute for a full fertilizer program. The 1-0-1 NPK means it delivers essentially no nitrogen or potassium nutrition. A lawn using Ironite alone is not being fertilized.
- It does not correct nitrogen deficiency, pH problems, or drainage issues that may be causing yellowing.
Head-to-Head Comparison
| Factor | Milorganite | Ironite |
|---|---|---|
| Primary function | Organic nitrogen fertilizer | Iron supplement |
| NPK | 6-4-0 | 1-0-1 |
| Iron content | ~2.5% | ~20% |
| Nitrogen type | Slow-release organic | Minimal (1%) |
| Burn risk | Essentially none | Low at labeled rates |
| Response speed | 2 to 4 weeks | 1 to 2 weeks (iron uptake is faster than organic N) |
| Best use | Regular lawn feeding program | Correcting iron chlorosis |
| Safe for all grass types | Yes | Yes |
| Corrects nitrogen deficiency | Yes (slowly) | No |
| Corrects iron deficiency | Partially | Yes |
When to Use Each
Use Milorganite when:
- You want to maintain a regular, low-risk organic fertilization program
- You are feeding any grass type with burn risk concerns (new lawns, sensitive warm-season grasses, summer applications on cool-season turf)
- You want a product that combines nitrogen and iron maintenance in a single application
- You are looking for a year-round organic fertility option
Use Ironite when:
- Your lawn is showing interveinal chlorosis (yellowing between veins while veins stay green) consistent with iron deficiency
- You want to improve lawn color during summer without applying significant nitrogen
- A soil test or visible symptoms suggest iron deficiency specifically
- You want to supplement iron between standard fertilizer applications
Use both when:
- Your lawn needs both nitrogen and elevated iron correction at the same time. Some homeowners apply Milorganite as their base fertilizer and add a separate Ironite application when summer chlorosis occurs, maintaining organic nitrogen delivery year-round while spot-addressing iron demand during the summer green color challenge.
The Deer Deterrent Factor
Milorganite has a well-documented secondary use as a deer and rabbit deterrent. The biosolid origin of the product produces a scent that many deer find repellent. This is not a function of Ironite. For homeowners managing deer browsing on garden plants and landscape beds adjacent to the lawn, Milorganite’s dual function as fertilizer and deterrent is a practical advantage.
Cautions with Ironite
Because Ironite delivers 20% iron, repeated applications can accumulate iron in the soil to levels that eventually cause iron excess or interfere with manganese and phosphorus uptake. Use Ironite when symptoms or a soil test indicate iron deficiency, not as a routine every-season application. For the signs of iron excess and how to correct it, see too much iron in lawn: signs and how to fix it.