Question
Hi Ken
I live in Stuart FL, zip 34996. I have a St Augustine lawn that I ALWAYS mulch when mowing. I'm noticing some yellow areas on my grass and my neighbor says I should put Epsom Salts  and start bag collecting my grass for a couple months to reduce the mulch thickness--grass goes very fast and is in good shape. I bought the Epsom Salts but now how do I apply it? I also bought some Aerator Sandals--spikes in bottom of sandals to walk on grass to aerate. How do I use these--and how often? Thanks. Mike

Answer
Yellowing of grass can be due to many factors. Thatch build up on st.augustine lawns is very well documented, however. Thatch is a thick layer of partially decomposed roots, stems, and runners which form an unpenetrable layer between the grass and the roots. Water, oxygen and nutrients can't reach the roots, and carbondioxide can not escape. You can walk on the lawn with your sandles to punch holes through the thatch layer (often 1/2 - 2" deep).
A better method is to rent a vertical mower (verticutter, dethatcher, etc) and run it over the lawn to thoroughly dethatch the lawn. If the lawn starts to turn yellow, this should help.

However, a lawn can also turn yellow due to lack of water, too much or too little fertilizer, insects and disease. Dethatching will not solve these problems.

You can cut a core of soil from the lawn and look carefully at the layer between the soil and the green growth. You will notice a brown (almost color of soil) of matting looking material. If this layer is more than 1/2" deep then I recommend dethatching. If in doubt, bring a few cores to a landscaper or professionally run garden center. Dethatching equipment can be rented, or landscapers will do this for a small fee. You may only need to do this every few years.

Epsom salt is a good source of magnesium and sulfate, but chances are that your lawn do not require excess of these. Epsom salt is often proposed by home owners and tv-gardening gurus for a varity of gardening problems, but in reality it will probably not solve your problem.

Make sure to water deeply when you water, fertilize on regular basis and mulch mow as you have been doing. If excess thatch is the problem, the best resolution is dethatching (the sandles are moderately effective at best). Until you dethatch, it is a good idea to catch the clippings, but then start to mulch mow immediately afterwards again.

Good luck