You probably heard that from someone who is in the business of taking $5 worth of dirt and charging hundreds to spread it out. In my opinion there is absolutely no value in that. There are hazards to the existing lawn, though. These can be time consuming and very expensive to fix.

What is the problem you want to solve with the topsoil?

In addition to compost, which I will never use again, you can start applying organic fertilizer now. I believe that is the best, most cost effective thing you can do for your soil. There is a house around the corner from me where they apply compost every other year. Every other year they smother the St Augustine and it takes until the following season to fully recover. I should take a picture but I'm waiting for the clouds to come to show it off just right. It has been since March when the compost was applied and the grass has not filled in yet. For St Augustine I believe compost is highly overrated.

My idea to use layer of topsoil is to add organic matter to my "sandy nothing" under lawn, previous owner have not mulched or fertilized for at least las 3-4 years, I can tell, lawn looks bad and soil is very high in pH and carbonates, I need to start somewhere to fix that.

Okay so the lawn looks bad. Before going any further, I would need to know where you live. Topsoil almost never contains any organic matter. The compost mentioned by tiemco is 100% organic matter. However, if you have sand soil, don't get your hope up too high for compost solving all your problems. Really need to know where you are.

How do you know the soil has a high pH? Again, depending on where you are, you can address that or forget about it. St Augustine grows extremely well at a pH of 8.5. Assuming you are there or below, then you might not need to do anything. I live on a limestone formation that extends 50 miles in all directions and is 700 feet deep. I'm never going to dissolve all the lime to get down to a pH below 8.

If you would like to have your soil/sand tested for chemistry, the best lab is Logan Labs in Ohio. Whatever your local county extension service is offering for $20 or less cannot match the depth and breadth of the $20 test you get from Logan Labs.

While you are waiting for results, you can get started with organic fertilizer to improve your soil. My favorite is alfalfa pellets for the amount of protein you get for the price. You can usually find it at any feed store. It goes by that name or rabbit/chinchilla chow. Apply at 20 pounds per 1,000 square feet. The more often you apply the faster your soil will improve. Monthly apps are fine. It will take a full 3 weeks before you notice the improvement, but it will really make a big difference in color, density, and growth. A 50-pound bag of alfalfa should cost around $12. After you apply moisten the pellets. They will soak up the water and burst which prevents other critters (mainly birds) from flying off with them. Feeding alfalfa to the soil is the fastest way to improve your sand/soil. If you absolutely cannot find alfalfa, try Milorganite, soy bean meal, cottonseed meal, or corn gluten meal. The last resort would be ordinary corn meal and used coffee grounds (free from Starbucks).

Obviously alfalfa is organic and will help develop the soil so that it destroys any thatch you might have. You should be watering once a week for an hour at a time. And you should be mulch mowing at the mower's highest setting once a week. If you are not doing either of those, correcting that is going to help, too.

I am in ft lauderdale area, 10 a/b zone, nothing will survive in 8.5 ph conditions, palms, hedges they all around in south florida gardens and lawns, what are you talking about? if you do care only about your st Augustine grass and nothing else around, take a break, there are more than that to be conserned about!

Hey I payed 30 $ per alfalfa bag , I do not care about numbers I just wanted to have healthy organic backyard, did I got that? Not sure, have I spend extra money? Surely, for what? No one knows besides organic lawn care ideologists, it is what is sound stupid!

What were the results? We are in south central San Antonio. Our land is like beach sand. Trying to grow bermuda. Was just thinking about applying topsoil. Brought in bermuda sod a few years back. Did great for about 2 years and slowly died back. Sand does not seem to hold the nutrients. Grows great between the rocks in our sidewalk and growing well through our roadbase driveway. Oh, and before I read this post I started the Alfalfa pellets last year. But it was kinda late when I did.

Any advice appreciated.

I think it's OK for topsoil or compost (the organic matter being a key difference), but don't put such a thick layer that your grass couldn't recover from it in a timely fashion. You are not "burying" or "planting" something, you are just adding nutrient or leveling up the area. If you have a lot of leveling up to do, work it in small portions over time.

At the same time, one of the primary methods of getting nutrient into the soil for the turf grass is to use the other products, not just compost. You can buy a ready-made mix or you can make your own concoction, but you'll have to research on the components you want and how much to add (such as some mixture of molasses, fertilizers, azomite, alfalfa, etc -- whatever you wanted to add in from your own research)

First to Tamie. Please post a new topic if you want people to see and reply to your bermuda issue. This topic is about St Augustine. Quick answer is don't add topsoil or compost. Add organic fertilizer at least once per year to keep the soil biology happy. The more alfalfa and more often the faster your soil will become healthy. I have used Von Ormy sand as fill in my garden for decades. It's good but you have to keep the organic matter fed.

Back to the OP.
I would strongly discourage you from adding topsoil for two reasons. The topsoil is going to change your drainage whether you like it or not. Compost will not change drainage. The second reason is that every single blade of St Aug that ends up buried underneath either topsoil or compost will die leaving a hundred bare spots in your yard. I see this in my neighborhood every single year. This one house applied compost/sand so heavily it will likely have the bare spots for two full seasons. They never learn. I've been there 20 years.

Soil provides no organic matter. If you want to replenish the organic matter in your soil, simply apply alfalfa pellets or any of the additives suggested by gardenper. Organic fertilizers replenish the soil biology by feeding them. Then they repopulate. Whatever you mix together, a safe amount to apply is 20 pounds of the final mix per 1,000 square feet. It's really usually safe to apply that rate for each and every one of those materials, but that ends up being a waste of time, money, and effort.

I have St Agustine grass doing poorly. Dead spots, really dead, soil showing with dead runners. I'm in Nacogdoches TX and it's averaging highs 95 degrees daily. Do I fertilize dead spots and add soil.or compost for runners around spots to take over. Plant new squares of grass??

Is it too hot to fertilizer now. I've looked at Sunday Texas brand to fertilize with, if I Should. No evidence of Grubs, chinch bugs or such.

I'm 84 lady so if anyone can advise, thanks!! Also no rain in a week so I just watered 1 inch on lawn. My bushes and gardenia are doing well, also. Thanks for any advice!!

Trisha, you should have started a new topic, but this one is not too long to make it unwieldy to read through.

Watering wrong is usually the reason for poor St Augustine performance. Assuming you have drainage away from the poor areas, then repeat the 1 inch watering every week. Measure 1 inch using tuna or cat food cans. Time how long it takes to get a full inch and write that time down to remember it. In my neighborhood with my water pressure, hoses, and oscillator sprinkler, it takes 8 full hours to get 1 inch of water. Your time will vary, so you have to get out the cans and do the test.

DO NOT GET MORE SOIL unless you do have low spots in the yard.

Another reason for dead spots is a fungal disease. Can you take a picture of the grass from a distance of 6 inches and post it here? I'll show you what I'm looking for.

Do you see the lesions on the grass blades? If you have those, then no amount of watering will bring it back. One thing that will bring it back is ordinary corn meal. If you have a large area to do, get corn meal at the feed store. Here is a link to feed stores in your area. The application rate is 20 pounds per 1,000 square feet. It's getting late in the year to treat for this disease, but it really does work. Usually it takes 3 full weeks and you'll see the St Aug coming back.

Dchall… you water your lawn for 8 hours to get an inch? Did I read that correctly? That’s insane.

That is correct. With my hose, my sprinkler on full sweep, and with my water pressure it take 8 hours to fill the cans. But at least it is the same inch that my neighbor gets in 20 minutes, so no water wasted. It's a very gentle application with the oscillator sprinkler. One disadvantage of the oscillator is if you live in a windy area and the water blows away out of your control.