it's definitely not nutsedge, which has a different and distinctive look. first question to ask yourself:is it the exact same grass as the rest of your lawn? if it is, then extra water or fertilizer in that area is producing extra fast growth. If it's definitely a different plant, then you have a weed grass in there. I've had that. Big mess. Hard to get rid of. Good luck

@ kimmsr... Not sure how recycled tires got into this discussion? @ OP... Just called the landscape company that supplies the mulch. It is called "Playmat" mulch. There is no dye in it and it is NOT put through a shredder, rather it is put through a chipper. They claim that it provides more cushion when it's not shredded. The mulch is also NOT heat treated. That's good stuff to know, although shredder vs. chipper is just a matter of particle size in the finished product. The ASTM standards for which play mat mulch is certified are in regard to moisture retention and erosion control. Here's a description of play mat mulch that I found: Play mat exceeds all ASTM (American Society for Testing and Materials) requirements and is superior in quality. Our virgin hardwood chips are processed to create mulch that is clean and free from twigs and leaves. Our playground surfacing compacts in layers to give incredible impact resistance, therefore, receiving one of the highest government safety ratings. He suggested to fluff the existing mulch with a rake and put another 4 inches of Playmat on top of it. This seems like an instruction that is in direct opposition to the results you want. Stirring up the mulch will allow more weed seeds to get to the soil. You could probably have a load of wood chips delivered for free via tree trimming service. The last sentence of the description I pasted above mentions compaction as a factor in impact resistance. If the person you called knew that, that should be more reason for them to not give you the "fluffing" instruction because the reason you have the mulched area is that it's under a play structure. I also asked for a herbicide recommendation and he mentioned that a number of his guests use a product called "Crossbow". I need to do some research on this product. Great idea, putting poison in a children's play area definitely warrants research. If you could go into the future and ask your grown children if they would rather have pulled weeds or played in poisoned wood chips, I think you will have done as much research as necessary, though.

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.

Pine Barrens? Marcus Hook area? You're near the end of the window, but you still have a little time. Grasses like fescues and rye will have time to establish. Kentucky bluegrass will be a bit more touchy, but you'd get at least most of it if you went now. If that general area is incorrect, the map will change... As DCHall said, I think I'd Round Up soonest, and mow down the weeds as short as possible before the seeding (bag the leavings this one time). We're getting late enough that I don't think I'd water and re-Round Up in a week as your first frost date (for Marcus Hook, the area I'm most familiar with) is November 14th. It gets too cold to reliably sprout grass seed somewhat before that. When you water to grow the seed (once per day absolute minimum, two to four times per day is better), you're going to make the weeds grow explosively. At seeding time, use a starter fertilizer with Tupersan in it. It's pricey, but it'll help suppress out some of the weeds. Not all by any sense (Tupersan is safe for grass seed and doesn't have a very wide range of weeds it suppresses), but it'll reduce your weed sprout a bit. Then, in spring, skip the weed and feed and spray with Weed B Gon. The weed and feed will feed the grass at the wrong time in the wrong amounts, and the weed killer isn't all that effective unless used exactly correctly either.