I have been asked this question many times. Unfortunately, their is not one easy answer that I can give you.
Why not? Moss is a product of a few different problems and usually you need to take care of all of them to keep the moss form coming back.
Do Moss Killers Work? Yes and No. They do work, but most of them Don’t solve the problem and it just turns the moss a dead orange color. You still need to rake it out and change the enviromental conditions that it favors. Until I was ready to take care of it the right way, I would rather see green moss than bright orange moss. Save your money.
Does Lime Kill moss ?
Let me say this. No, lime does not kill moss. Never did. Its a popular misconception because Lime increases PH and moss usually likes acidic (lower PH) soil. Adjusting your PH will help, but it wont kill any moss you have. More on Ph below.
Well, how do you get rid of moss then?
Moss is usually a product of Shade, low PH, bare spots, moisture and drainage problems.
It is most commonly found in the shade (but not exclusively) where grasses don’t usually grow real well. It prefers acidic soil (low PH) and likes moisture.
I would try these steps:
Rake out the moss with a hard rake.
Try pruning nearby branches to allow even a little more light in
Adjust PH. Lime is fine, but can take 4-6 months. Try using a product called Solu-Cal. It works real fast and that speed may help prevent the moss from coming back. It will also create a better enviroment for any seeding you do.
Try seeding with the proper seed to fill in the bare spots. If its shade, then a quality shade seed. Heavy shade will be difficult to grow grass, and that is a topic for another day. If you need help see my previous post Selecting Grass Seed. You will need to water it to germinate it.
Try improving air flow and/or drainage in the area. The pruning will help. Aerating deeply may also help. Incorporating some organic matter may also help.
Once grass is germinating and the moss is out, try to maintain the PH levels with regular Lime or Solu-cal use. You don’t want to give it an invitation to come back.
One last thing.
I have seen moss in full sun and in thick lawns. In these lawns, I would suspect the PH to be low and compacted soil. I usually see moss in the full sun in newer lawns. New developments in wooded areas that are 10 years old and less seem to have the most trouble. I suspect it has something to do with excavating the wooded area that naturally contained moss to build the houses. They also drive many heavy machines all over the place to build these developments. This creates heavily compacted soils that don’t drain well. Contractors usually bring in 2-3 inches of topsoil on top of these native compacted soils so you could have a compaction problem even if the top 2-3 inches is aerated and drains well. Once it gets below that layer is when it runs into problems.
In cases like this, Correct the PH and do your best to improve drainage. Maintaining a proper fertility program will also help .
Here are a couple other links to moss help from universities. they pretty much sum up what I explained here, but some other points as well.