Why Is My Lawn Yellow Even Though I Fertilize? Iron Chlorosis on Hill Country Soil
You fertilized. It rained. And the lawn is still yellow — maybe yellower. Around Burnet, Marble Falls, and much of the Hill Country, that’s usually not a feeding problem at all. It’s iron chlorosis, and no amount of regular fertilizer will fix it.
What’s actually happening
Much of the Highland Lakes sits on limestone and caliche. That rock makes our soil alkaline — pH often 7.5 to 8.2. At that pH, iron in the soil gets chemically locked into forms grass roots can’t absorb. The iron is there; the grass just can’t touch it.
Grass needs iron to make chlorophyll — the green. No usable iron, no green. So the lawn fades to yellow-green, then yellow, even while it’s being fed and watered perfectly.
How to tell iron chlorosis from other yellowing
- The stripes tell the story. Iron chlorosis shows up as yellow leaf blades with green veins — a faint pinstripe look, most visible on newer growth.
- Nitrogen deficiency yellows the oldest leaves first and shows no striping — and it responds within days to fertilizer. If feeding didn’t fix it, it probably wasn’t nitrogen.
- It gets worse after heavy watering or rain, in compacted areas, and in St. Augustine more than Bermuda.
- Patterns follow the soil. Yellow patches over buried caliche or builder’s fill, green where topsoil is deeper, are classic.
Why more fertilizer makes it worse
Pushing extra nitrogen forces the grass to grow faster, which dilutes what little iron it has — the new growth comes in yellower than ever. Some phosphorus-heavy fertilizers also bind iron further. This is the most common self-inflicted lawn problem we see on Hill Country caliche.
The actual fix
1. Confirm it with a soil test
A lab test tells us your pH, your actual iron availability, and what else the soil is hiding. It turns the program from a guess into a prescription — the same way turf is managed on a golf course, where chlorosis on a fairway isn’t an option.
2. Chelated iron, not iron sulfate
On alkaline soil, plain iron sulfate gets locked up almost as fast as you apply it. Chelated iron (look for EDDHA chelation on high-pH soils) stays plant-available and greens the lawn in weeks, not months.
3. Feed to the soil test, not the bag
The right nitrogen rate, no unnecessary phosphorus, and applications timed to the grass’s growth cycle keep color steady instead of cycling yellow–green–yellow all season.
You can’t practically change the pH of caliche ground — but a program built for alkaline soil makes the pH irrelevant. That’s the difference between treating the symptom every summer and solving it.
Want this handled for you?
Texas Turf Pros builds and runs weed control & fertilization programs across the Highland Lakes — Kingsland, Marble Falls, Horseshoe Bay, Burnet, and Llano. TDA-licensed, run by an owner with golf course superintendent experience.
Quick answers
Will iron chlorosis kill my lawn?
Not quickly, but chronically iron-starved turf thins over time, and thin turf invites weeds and disease. Lawns that stay yellow through summer are also far more vulnerable to drought stress.
How fast does chelated iron work?
On a correctly diagnosed lawn, visible greening typically starts within one to three weeks. Because alkaline soil keeps locking iron back up, most Hill Country lawns need it as a recurring part of the program, not a one-time fix.
Can I just spread a bag of ironite?
Store iron products help briefly, but most rely on iron forms that alkaline caliche soil locks up quickly, and some stain concrete badly. A soil test plus properly chelated iron at the right rate is cheaper than repeated bags that don't hold.