Moss grows in soils that are compacted and too wet, soils that lack adequate levels of organic matter, although I have moss growing in full sun on loose sand. Moss is a first stage plant that Ma Nature grows in soils that need more organic matter so higher order plants can grow there. Correct your soils problems, add organic matter, and the problem with the moss will go away without spending money, needlessly, on something to kill what Ma Nature put there to try to correct a problem.

In your photo there are LOTS of little seedlings, which means there must have been lots of seeds in your lawn or in the compost you put down. You didn't mention the lawn having lots of weeds previously so I wonder about the compost. Where did it come from?

Your options are limited while the new grass is just getting started since many broadleaf herbicides can damage the grass seedlings too. If you wait until the grass is established at least 8 weeks, then you may be able to use herbicides. Check the label of any product before using it on new lawns.

I agree with kimmsr that correcting soil problems is the way to manage moss in a lawn. Moss is not a competitive plant, as you can see by the very limited root system it has. It grows in lawns where the grass is already doing poorly. This can be cause by lack of soil fertility (the most common cause in my experience), too much shade, heavy soils that drain poorly, and excess acidity (pH below about 5.2). Lack of organic matter isn't normally limiting for grass, but adding organic matter can improve drainage if that is the problem.

Have you had a soil test done? You mention that the soil was determined to be acidic. What was the pH?

Daniel, moss may not be a competitive lawn plant in many areas, but if you are on the W side of the mountains here with our acid PH and ample rainfall, it's a constant problem in otherwise healthy lawns:)

You have more than one weed growing there and while it's at a very young stage, the seedling most numerous is looking suspiciously like Cardamine/shotweed, aka bittercress...you may have raked dormant seed to the surface light, or it could have come in with your compost. If it is bittercress, it will begin to form little white flowers here in winter - please don't let it go to seed or it will plague you for years.

I keep moss to a minimum (still a little in shadier areas) by aerating every year (rent a plug removing type machine) and several years ago I switched to slower acting organic fertilizers only...Ringer Lawn Restore has been one good brand.

My lawn isn't the main focus of my garden, but with our more unique-to-moss climate, you might get more hands on advise on the Northwest Gardening forum where just about everyone deals with problem moss at one point or another.

Thanks for your responses!

botanybob: The compost I used was from Lowes. Probably not the best, but I'm pretty new to this :P. As far as the pH. I used a home testing kit that said the soil was approximately 5. Do you recommend any herbicides that would be good to use? Is there any good way to add organic matter to soil?

morz8: I live north of Seattle, so I feel your pain in terms of ample rainfall :). Thanks for your advice, I'll go checkout the Northwest Gardening forum.

If that soil test can be believed it is no winder you had moss growing and since the best method of controlling moss when the soils pH is low is to correct the soil conditions, not be spraying some poison, you need to contact your local office of the Washington State University USDA Cooperative Extension Service about have a good, reliable soil test done and what would need be done to correct that soil problem. If your soil pH is that low your grass will not grow well and the "weeds" will alwaus be a problem.