Hi Rich! I have the same exact problem! Where did last years lawn go? All the weeds I killed of last year have come back with a vengeance! Looking forward to some advice on this myself!

Well, once the irrigation went down for the count, the St. Augustine lawn we had slowly started to fade away...it seemed like in patches...we tried to keep it up by mowing (we hired a lawn care company to mow), but without the irrigation, it seemed like the weeds flourished where the grass couldn't (maybe the weeds were more dry/hot resistant). Now, I only see a few patches of actual grass (and I think it may be crab grass, not the ol' St. A stuff).

First, there is no St Augustine seed, so you can't do that.

Second, once the sprinkler system goes, you have to buy a hose or two and a sprinkler. I recommend the turbo style oscillator sprinklers because they apply the most even pattern and coverage along with a very slow application so the water can sink in. I have a house now where I turned off the automatic system and use only oscillator hoses. They cover the area much better than the center-throw pop-up heads.

St Augustine is pretty easy to grow once you figure out how to water it. Like every other grass out there, it needs to be watered deeply and infrequently. Deeply means 1 full inch every time you water. If it rains 1/2 inch, then you need to add another 1/2 inch. Infrequently means no more than once per week in the hottest heat of summer and less often when the weather is cooler. With temps in the 80s, you should go up to 2 weeks between deep watering. Most people in Florida seem to want to water a few minutes every day. That process develops grass with very short roots. Short roots are intolerant of drought, so if you miss a couple days of watering, or if one of your sprinklers clogs or breaks and you don't notice it, you could lose a lot of your lawn. But if you are deep watering on an infrequent basis, the roots will develop deeper down into the soil/sand and be much more tolerant of head and drought. Also weed seeds practically rely on daily watering to germinate. When you deny the water from the weed seeds, they will not germinate and develop into plants. So you can almost eliminate new weeds without any preemergent or other herbicides simply by controlling your watering.

Mowing

Always mow St Augustine at your mower's highest setting. There is never any reason to lower the deck. Tall St Aug provides shade to other plants, grasses, and weeds that might be trying to grow. Dense St Augustine will be the dominant plant in your yard.

Fertilizing

With your sand I strongly urge you to use nothing but organic fertilizers on the lawn. These will build the organic matter in your soil rather than deplete it like chemical fertilizers. Organic fertilizers feed real food to the microbes living in the ground. Those are the organic matter that matter. My preference for organic fertilizer is either alfalfa pellets (Rabbit Chow) or ground corn meal. Corn is very inexpensive this year...at least in my neighborhood. Corn is also relatively low in protein, so I tend to use it fairly heavy at 20 to 25 pounds per 1,000 square feet. Alfalfa pellets can be used at 20 pounds per 1,000. Call your local feed store to get prices for a 50-pound bag. Be sure they understand you want alfalfa pellets and not bales of alfalfa hay. And be sure they know you want corn meal and not corn GLUTEN meal and not deer corn. I start fertilizing with organics about now then repeat on Memorial Day, 4th of July, Labor Day, and Thanksgiving.

If you do those three things, and note that you were going to mow and water anyway, the only cost is for the fertilizer. You should have minimal weeds.

Now...how do you get St Augustine reestablished in the yard. Since you don't have money then you must have patience. If you can afford to buy a few pieces of sod, you can reestablish the lawn in a couple of seasons. Most recently I've used Floratam, but you have to use what you can get locally. I like Floratam because it seems to grow faster than disease spreads. It is a dense turf that loves full sun. Prepare the ground by clearing out anything that's growing and place the sod down. Start watering it lightly at breakfast, lunch, and dinner time every day for 2-3 weeks until the roots have grown down into the soil underneath. Once that happens you can start to water longer and less often. You're trying to develop those deeper roots. You don't have to water the weeds at all, so a hose and hand sprayer is fine for now. When the temps are between 65 and 85, St Augustine spreads and spreads. In my neighborhood that happens in the spring and again in the fall. I get about 5 feet of runners each time for a total of 10 feet of spreading per season. Your mileage will vary.

Back on the topic of mowing, I have a house where I mow it with a string trimmer down to 12 inches high. When it gets up to 16 inches or so I cut it back down. If I had a push or riding mower that would mow that high I would keep it at 12 inches. That's not great for playing in but it looks perfectly manicured, uses almost no water, and seems to need much less fertilizer to stay dark green. Also, since it's so tall and never gets anything but rainwater, there are no weeds or disease. I'm not necessarily suggesting that for you, but I am suggesting that if you were going to neglect something, neglect mowing and let the grass get much taller.