St. Augustine grass turning yellow

[tommy compton]

I have a st. augustine lawn that has taken a turn for the worse. It has been green and spreading since it was planted two years ago. In the past month it has began to turn yellow and I would like to know what to do to save it. I have watered twice per week and last year this seemed to be the correct amount of watering to keep it green even during the hot summer. Any suggestions or comments that might tell me what is wrong?

[Dchall_San_Antonio]

Hi Tommy,
I need to know more about your situation.

Where do you live? If Texas, please give distance and direction to the nearest big city?
How much do you water when you water?
What would you call your soil? (for example clay, sand, caliche, forest floor, etc.)
Have you had any drenching rains this summer?
Does water seem to puddle up anywhere when it rains or you irrigate?
Have you applied any fertilizers or compost since May?
Have you applied any chemical fungicides, herbicides, or insecticides this season?
Is the yellow color over the entire yard or spotty?

I need the info so I don't give you a South Texas answer if you live in East Texas or on some different soil or you're in a drought, or any of another conditions.

[tommy compton]

To answer your questions, I live 40 miles northwest of Waco in central Texas. I have watered with a single sprinkler covering the entire yard for about one hour in each area. The soil is mostly black dirt and some sand around the foundation area. The water does not puddle in areas when it rains.We have had some drenching rains over the past three months. I have not fertilized since may and some diazinon has been used once to treat for ants. The yellow color was spotty at first and is now taking over the entire yard.

[Dchall_San_Antonio]

Okay that's good stuff. It sounds like the rain may have had something to do with it. You should have fertilized in July but that might not be the current problem.

When we grow turf on our calcium based soils, we establish a very small zone of relative acidity. Right in the root zone the microbes will ply their trade and create humic acids that buffer the pH at or near 7.0. But when we get drenching rains, the effect of the buffer is overcome by the enormous amount of water flushing through. The effect is the iron in the soil goes from being available to unavailable at the new higher pH. So the grass will turn yellow seemingly overnight.

The solution for that condition is to use glauconite. It is bagged and sold as Texas Greensand and a few other names that always seem to include greensand. Glauconite is a subsea mineral deposit that is now above the sea. When you look at the chemical composition, it has a little bit of everything in it including iron and some other things. I'm not sure what happens chemically with glauconite in the soil, but the immediate (and long lasting) effect is to release the iron back to the grass.

You can apply glauconite any time but it should last at least a year or more depending on how much rain you get and how alkaline your soil is.

Plain glauconite does not go through a spreader very well so it seems to work best when mixed with some corn meal or something dry and then spread. I scatter it by hand. I put it on my daughter's wagon and reach in with a 64 ounce cup from Stop-n-Go, scatter the cup, and move to the next location.

If iron is your problem, you can apply fertilizer from now on and you won't green up. It needs the iron. I've used Ironite but consider it a waste of money. Greensand is what works for me.