Zone 8? What kind of grass?

Is it water soluble? Maybe it's supposed to be sprayed on as a foliar application. If so, don't do it if the highs are going to be above 80-85 degrees in the next 5 days.

Question: why do you think your lawn needs iron? Has it given you some indictation it needs such.

Any complete fertilizer will have the trace elements that lawns benefit from. The zinc, molebdymum (sp), et al, includes iron.
The package of lawn fertilizer will say what it contains and if it doesn't stipulate it has the trace element 'iron' in it, then pick another bag.

When you fool around with elements that your lawn and soil do not need, many times what happens is you come crying back for advice about "whot happend"...

The only sure way to tell if your soil needs iron is to get a soil test. Such tests are commonly done by nurseries, garden centers, extension services provided by many STATE universities and or agricultural colleges.
A state university is one that is supported by the state government and is not privately governed.

There are other methods to give your lawn 'iron' if it so needs it. Packages of chelated iron are found on shelves everywhere and directions for use is given.

Iron is not specifically for "greening" up a lawn...actually, nitrogen does a pretty good job of doing this when given in early spring.
Nitrogen, when given in too much volume, can cause problems by lowering the pH too much to the acidic side and often people make a habit of giving their lawn some lime to counteract high nitrogen readings.

Generally, most people who do give their lawns lime do not harm it any way---the lawn can accept the amounts of lime without causing undo harm. Only by getting a soil test can one be assured they are doing right by their lawns.

I wanted to green up the lawn just for appearance sake- I used Scott's organic for the summer. I really don't like to use synthetic in the heat. The Scott's does not list iron as an ingredient and I like that deep green look without pushing growth in the heat. It's mostly SA and I notice that sometimes synthetic increases leaf spotting- Anyway took the chance and applied Fri night then let the sprinklers water later- temps were 100 on Sat but everything looks fine- it was cloudy and cooler with rain today so that worked out well. I've never actually heard of anyone liming their lawn around here- they do sell it in the stores here so somebody must be using it for something. I do know most soils here are on the acid side- I rarely see any azaleas that are chlorotic. Maybe someone is using it in their veg gardens but never heard of it either.