Now would probably be the best time but you'll have to do some prep work first. Why now? Because the grass is growing as fast as it will grow. By leveling when the grass is growing fast you minimize the chances and severity of smothering. If you have areas where it is deeper than an inch, you should probably pretreat now with sand. I think you can use any kind of sand but there is a good argument to use builders' sand (not playground sand). Playground sand remains loose like pea gravel. Builders' sand should lock in and give you a firmer surface.
Here's how you do this.
- Fertilize any time but preferably 2 weeks prior to doing the leveling.
- Mow the grass down as low as your mower will go. This will probably take a couple weeks of mowing twice a week.
- Mow one last time.
- Spread sand everywhere.
- Level the sand with a drag made from a 5-foot (or longer) piece of chain link fence connected to a rope and with some weight on top. I used a 2x4 and tied the rope through the fencing to the 2x4. Then I added weight to the 2x4. Drag in all directions until you think it is level. If you have a riding mower this goes very easy. Otherwise your wife will get tired pulling the plow all afternoon in the heat
- Roll the sand down with a water fillable roller.
- Water the sand to settle it. Let that dry but not completely.
- Add more sand where you think you need it and repeat steps 4-6 again.
- Repeat 3-6 until you have it perfect. When all is done you should not have raised the surface of the soil except in the low spots. Your original high spots should still be the same height.
- Serve pizza and beer to the people who helped you.
- Water it 3x per day for 10 minutes each time for 2 weeks until the grass peeks back out. I know this is too frequent for normal lawns but this leveling process is not normal.
St Augustine is very easy to smother. What you are doing with the drag is helping to pull the short St Aug blades out from under the sand. Only those blades sticking out from the sand will survive this process. That is why you should pre-fill the deeper areas.
The proper amount of weight for a roller is enough so that your foot prints behind it are not showing. It really needs to have some weight. This will not compact your soil. It will help settle it. Settling takes 3 years unless you help it along. That is probably why you have bumpy soil now. It was probably tilled prior to sodding. Tilling is the fastest way to an unsatisfactory lawn.
If you buy too many bags of sand, you can return it later. If you buy not enough sand, you will have to stop in the middle and go get more. Be sure you have everything you need before you start.
Keep a push broom handy. It can be used to dress the surface of the sand and help bring the St Augustine blades up.