Our HOA has always kept our St. Augustine lawns mowed to 4" to 4.5" and the grass was always green and full. A new contractor began mowing to 3". Since that change the crabgrass has grown through the St. Augustine, resulting in large brown weed patches allover the lawn. I've been told by a large, national lawn company that grass height for St. Augustine should always be 4" to 4.5". What is the optimum mowing height for an established grass?
I would trust the lawn company. This should only be pruned down to about 4 inches. Any lower risks killing off the grass, or leaving it unable to grow properly.
The gentleman that treats our St. Augustine lawn called it floating lawn, The lawn doesn't seem to be attached to the soil. What causes this and what can I do about it?
I would talk to your local extension service to find out the exact cause, because it can have several. Usually fungal but it could be due to dry compacted soil as well. This link will take you to a page that you can find the closest extension service to you: https://www.gardeningknowhow.com/extension-search/
This website is dedicated to find issues similar to yours: http://neilsperry.com/2008/04/identifying-issues-of-st-augustine-lawn-management/
There are spots of the newly installed grass that is brown and dying. It is getting enough water so what else can I do to save it?
You should be watering your sod two times per day for 15-20 minutes. Our recommended times are (8:00 am, and 1pm). After 2 weeks please shut off your water for 1-2 days and let your SOIL dry out a little bit so that you can walk on it.
After your lawn becomes established it requires approximately 1 ½ inches of water per week, ½ inch every other day, during the heat of the summer. Spring and fall may only require once or twice a week watering depending on weather conditions. Cut water back during the winter, sometimes your lawn will only require watering once or twice a month, depending on weather conditions.
The soil should be soaked through when watered. Water should penetrate at least 6 inches into the soil to insure deep rooting.
Are St. Augustine and fescue grasses suitable lawn grasses for zones 5a/5b, northern Illinois. If not what is recommended?
St. Augustine grass will not likely survive well in your area. Fescue will be barely hardy in your area. These grasses are too warm natured, and too cold natured, respectively.
This article will give you some better suited grasses for your area: https://www.gardeningknowhow.com/garden-how-to/gardening-by-zone/zone-5/zone-5-native-grasses.htm
What type of fungicide do I use to get rid of a fungus on St Augustine grass?
Your first step is identifying which type of fungus you have. There are several that affect St. Augustine grass. The Florida Master Gardeners can help you figure out the problem. Find your local office at Search.Extension.org. The following article discusses 2 fungal diseases that affect St. Augustine grass; perhaps you can figure out which you have. That done, you can find the right fungicide. Other prevention tips are included. https://www.abchomeandcommercial.com/blog/yard-fungus/
I just bought a home in south Florida. The lawn is pretty patchy. More weeds than St Augustine. What is the best way to get rid of the weeds and fill in with thick St Augustine?
You can use a post-emergent herbicide to kill as many weeds as possible, then overseed with grass. First determine if the patchiness is due to disease. You may want to consult your local Extension agent for help determining which disease. Here's information on lawn disease, overseeding, and St. Augustine grass:
I am pulling these sprouts, but is this a sign of fungus or root rot? How to treat??
Apparently the grass runners won't reproduce on dry soil, thatch or compacted soil, so they keep stretching. Prevention is proper mowing height, about 2 1/2 inches, proper fertilization, avoid overwatering, and adding a light helping of compost to the lawn in spring to aid soil health.