Kill moss in lawn - Is product Fiesta safe to use

Asked April 9, 2020, 3:15 PM EDT

Hi. We live in Montgomery County, and new laws have been put into place limiting what product landscapers can use for lawn maintenance. We asked our landscaper if he can help kill some mossy areas in our lawn. Our lawn is about 1 acre. He suggested treating the entire 1 acre with a product called Fiesta, which contains iron that will kill moss. He suggested two applications a few weeks apart. A few questions I have: 1) Is Fiesta safe in your opinion to use broadly on our entire lawn? 2) We're on well and septic. Is there any concern with respect to well water when using Fiesta or an iron based product? 3) Is this the right approach, or do you recommend our landscaper use something else? Thanks.

Montgomery County Maryland

1 Response

Fiesta is a very expensive product and a temporary fix. (Check the label or call the manufacturer for safety questions, but it should be safe. Iron occurs naturally in Maryland soil.) We'd recommend a different approach.

Moss does not "kill" lawns. It merely moves in when turf is weak or thin. So, the question is, why? Moss likes or tolerates: shade, wet soil, low fertility, soil compaction, and low pH (acid soil). Grass does not like any of these. If you simply kill the moss and do not address the underlying problems that encouraged the moss, it will just return.

If you have a lot of shade from trees, consider rethinking the landscaping there. Grass does not grow well in shade (if at all) and a huge amount of work and money is wasted trying to get it to do something that runs against its DNA.

Here is our page on moss, and how to address it: https://extension.umd.edu/hgic/topics/moss-your-landscape (Click on "Moss in Lawn" for more specifics.)

Ellen