# Is it too late to add Ferrous Sulfate to reduce the pH of my lawn before applying fertilizer?



## Skrepo (Jun 23, 2021)

I have a question about applying ferrous sulfate to reduce the pH of parts of my lawn at this time of year.

I tested my soil where there is no growth and found that potassium and phosphorus levels are sufficient but nitrogen is severely low and the pH is hovering around 7.5 to 7.6. I checked my soill type and I essentially have loam, some sections sandy loam, and one area that is clay loam.

On a reference that I found in a book, it was recommended that one apply 1.5 lbs of iron sulfate per 100 SQ ft for 0.5 pH drop or 3 lbs per 100 SQ ft for a 1.0 pH drop with a loam type soil

Now to my understanding if the pH of the soil is not sufficient in the pH 6.0 to pH 7.0 range any amount of fertilizer goes to waste as the nitrogen cannot be properly used. I have heard of people combining ammonium sulfate with ferrous sulfate but the amount I'm using is sufficiently higher and that people using the ammonium ferrous sulfate are using it to grow and green up their lawn that I'm presuming is at least decent.

I live in coastal Orange County California and unlike the rest of Southern California we haven't really experienced a heat wave yet. The highest it's been has been about 83-84 with 74-76 being the norm in the shade at ground level. That said, the lawn in question is in the sun 10 to 12 hours a day, north facing. All the great looking lawns in my area are either east or west facing so they do not get nearly as much sun as I do

Is it too late for me to set down the iron sulfate on the soil at this moment in time within the confines of summer to lower the pH? I would like to add fertilizer to my lawn to keep it up to snuff as it is showing distress but I don't want any unutilized fertilizer to run down to other parts and burn the grass that I still have.

Any help or insight would be appreciated

The picture below is where I did one of the soil tests and the nitrogen test, along with the pH test. I used a pH meter mind you to get a more exact answer


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## g-man (Jun 15, 2017)

1.5lb of FS/100sqft is 10.5lb of FS/Ksqft. This will be a good way to kill your lawn. I think the recommendation you read is for gardens to address the soil before planting.

The pH is not bad and it is not the reason for issue with your lawn. A soil test via a lab will be give you more accurate results than the home test. The first post in this soil folder has info on some options.

Based on the image, i suggest you check the watering (1.5in/week?) and do a spoon feeding of nitrogen to see how the lawn reacts. The cool season guide in my signature has general information that should help get you in the right track.


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## corneliani (Apr 2, 2019)

Gman is saying exactly what I was going to say. This recommendation is not for existing lawns, for sure. There are weed killer products out there that use Iron Sulfate as their main/only ingredient, at a much lesser rate than you mention.


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## Skrepo (Jun 23, 2021)

g-man said:


> 1.5lb of FS/100sqft is 10.5lb of FS/Ksqft. This will be a good way to kill your lawn. I think the recommendation you read is for gardens to address the soil before planting.


I'm confused because even the link below indicates one to use ferrous sulfate on an existing lawn but at a higher level to decrease pH

https://homeguides.sfgate.com/make-lawn-acidic-90957.html


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## g-man (Jun 15, 2017)

This is an article from Purdue university on lowering soil pH. Lowering it without killing your lawn is tricky. If you want to do a test of 10lb of FS/ksqft, take before and after pictures of your lawn so we can see the results.

https://www.extension.purdue.edu/extmedia/ho/ho-241-w.pdf


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## Skrepo (Jun 23, 2021)

g-man said:


> This is an article from Purdue university on lowering soil pH. Lowering it without killing your lawn is tricky. If you want to do a test of 10lb of FS/ksqft, take before and after pictures of your lawn so we can see the results.
> 
> https://www.extension.purdue.edu/extmedia/ho/ho-241-w.pdf


Thank you for that! Ideally is it alright for me to do soil amendments this late in the season. I see mentions of fall so you are ready for springtime but nothing that specifically says that it is a huge no no during the summer.

My main worry is the battling of the dormancy of the grass during the summer months while simultaneously changing the pH a bit quicker than just laying down Sulfur.

Thinking of just doing a gentle top dressing over the next couple months while throwing just a tad of nitrogen out and see how the grass responds. I have been watering definitely, but with the pending drought in my neck of the woods it remains to be seen on the potential cutbacks that may be happening.in the near future


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