what is the best method/product/timing for removing moss from the lawn?
Multnomah County Oregon
The easy answer is Lilly Miller Moss Out - a liquid iron product. The more water you can apply with it the more effective it will be. However, there are 3 possible strategies.
The first strategy is to do nothing and let the moss naturally recede as temperatures warm up and the rain stops. Moss fills a niche in Oregon during the winter time when the lawns thin out and then it will often recede in the summer.
The second strategy is to apply a moss control product like Lilly Miller Moss Out which is a liquid iron product, or apply a fertilizer with iron, which is less effective. There are also fatty acid "soap" products that have been less effective in our trials but they turn the moss a light brown color (which is less ugly) versus a black color which is what the iron does. Most people find the black color ugly. Also, some people view fatty acids as better for the environment than iron products. The problem with this strategy is that you usually don't really kill all the moss completely but rather injure it and most of it grows back as soon as the rain returns. One thing to keep in mind is that moss does not take up the chemicals like plants do so you have to touch all parts of the moss plant to kill it. The upper portions of the moss often insulate the lower portions.
The last strategy is to completely irradicate the moss which takes a lot more work. There are 3 steps: first you rent a dethatcher and dethatch the lawn and remove most of the moss. Next, you apply Lilly Miller Moss-Out with as much water as you can to really soak the moss (or another product if you don't like this one). Finally, you fertilizer your lawn with 2 lbs of slow release nitrogen per 1,000 sq. ft. Each fertilizer lists a ratio on the bag (e.g. 25-5-10) which states what percent is nitrogen, what percent is phosphorous, and what percent is potassium. To calculate how much fertilizer to apply 2 pounds of nitrogen per 1,000 sq. ft., you divide 2 by the nitrogen percentage. So if your fertilizer is 25 % nitrogen (e.g. the bag shows a ratio of 25-5-10) , then 2/.25 = 8 lbs of fertilizer per 1,000 sq. ft. Of course, this will cause you to grow more grass and you may have to mow it more often for awhile.
This last approach will erradicate the moss but it doesn't mean it won't grow back next year if you have a wet or shady site, or you don't fertilizer your lawn enough to keep it's density. Perennial ryegrass is terrible for losing density in the winter if it is not fertilized regularly - even in the winter. Moss reproduces by producing spores that blow in or vegetatively by pieces breaking of and getting tracked. By the way, more frequent and lower mowing makes the grass denser, so good mowing can make a HUGE difference in turf quality. For perennial ryegrass, don't mow below 1.5 inches.
Moss has been around since before the dinasaurs so it's not going anywhere soon.
Brian, many thanks for your help. Will report back in a few weeks after we try to get rid of the moss.