Can You Use Lawn Moss Killer in Winter?

mossy lawn

It’s about time for a moss care 101 article on DreamyHome – luckily for you, that’s happening right now! Moss is one of those things that can be beautiful when controlled, but it’s also generally a sign of other, more serious issues. As such, a common tactic for homeowners is to regularly apply moss killer. But the question arises of when to apply it. Can you use lawn moss killer in winter, or does it need to be applied in the thick of summer?

In short, there’s a specific stretch of time between late winter and early spring in which moss killer is the most effective.

There’s quite a bit to cover today, so let’s just dive right in. We’ll get your garden sorted in no time, and you get to learn in the process!

Moss 101


Let’s start with the super basic stuff: what is moss, why does it occur, and is it harmful to you or your home? We’ll get to moss killer shortly after, it’s just important to know why you’re killing the moss in the first place (if you don’t already).

If you live in a particularly rainy area (the UK, perhaps…), then you likely already know what I’m about to say. Moss thrives in damp, relatively cold (not freezing, usually), and shaded areas. People often complain of seeing patches of moss pop up on their lawn, with it sometimes even replacing the grass.

This is an especially common occurrence in particularly acidic soil, as it further boosts the growth of moss. Coincidentally, acidic soil is quite bad for lawns. This means that assuming you meet some or all of the qualifiers, you’re likely to battle with moss for ownership of your lawn.

While this will bother some homeowners, there are plenty of others (myself included) who find that moss brings a sort of charm to most homes when contained properly. And luckily, moss isn’t harmful to you or your home, though it may signify issues with moisture if it’s on your home. It’s also a surefire way to see grass die if you allow moss to thrive in your lawn.

And that brings us to today’s topic of discussion – when and how to apply moss killer.

When & How to Apply Lawn Moss Killer

mossy lawn

First things first – let’s clarify exactly when is best to apply lawn moss killer.

Generally, the best time to apply lawn moss killer is in late winter (~January) to early spring (~March). This is because moss grows the most during spring, like most forms of plant life. So if you want to cut it off before it can grow and spread, you’ll want to apply moss killer when it’s still preparing to, well, spring forth.

Generally, you’ll want to look for moss killers that will negate the soil’s acidity. Common ingredients to look for are ferrous sulfate and ferrous ammonium sulfate, though copper sulfate and potassium salt variants will often do the trick, too. Keep in mind that you want to use this soil later – so don’t opt for heavy-handed all-purpose weed killers. It’s also worth noting that both copper sulfate and potassium salt have the potential to kill your lawn in the process.

Another thing to keep in mind is that, as mentioned above, moss likes shady, damp environments. This means that targeting the causes of these factors will further reduce the need for future treatments. Trimming tree branches and moving things that can be in order to allow more light will naturally discourage moss from growing.

How to Apply Lawn Moss Killer

Ideally, you’ll apply the first treatment of moss killer in late January-early February. This allows the killer to do its thing while giving the soil enough time to recover. By enabling this recovery period, you prime the soil to accept new growth. Whether that new growth is grass, veggies, or something else is up to you, but do the replacement the favour of allowing it the time it deserves.

As for the actual process, just look below:

  1. Rake up any refuse (dead grass, leaves, etc.) in the problem area.
  2. Break up (till) the soil where the moss in question is growing. You can use a rotavator for this if you have one.
    1. This loosens its hold and breaks up the compacted soil that moss loves so much.
  3. Apply your lawn moss killer (likely in granular form) and water the lawn after applying your killer.
    1. This helps distribute the moss killer deeper, preventing any pesky moss spores from escaping and popping up next year.
  4. Wait for a minimum of two weeks (preferably a month) to plant new growth.
    1. This allows the killer time to do its thing and gives the soil a break to recover. Obviously, plant new seeds when they need to be, so wait longer if necessary.

How to Stop Moss From Coming Back

mossy garden with bird

So we know what moss likes – acidic and compacted soil, shade, and damp conditions. While we can’t make your neck of the woods rain less, we can target the other symptoms to prevent moss from returning. Conversely, you could improve these symptoms if you want to encourage moss to grow and let nature do its thing.

So look for the following to prevent moss from returning:

  • Target acidic soil with pH treatments.
    • This will not be a cure-all treatment. Rather, it makes the soil more welcoming to other plants. Moss is surprisingly adaptive and will find a way to survive in less than ideal soil if given the chance. So in short, always treat soil acidity as a secondary measure and have a primary plan in place to actively deal with the issue.
  • Remove shade when possible.
    • This can be anything from a garden umbrella/cover to tree branches. If removing the source of shade isn’t an option, may I propose that you embrace the moss?
  • Break up your soil regularly.
    • This is just gardening 101 – tilling the soil makes it easy for “good” plants to grow, and (usually) harder for “bad” plants to grow. Moss loves compacted soil, so breaking it up makes it that bit less likely to stay.

And that’s about it! Moss is hardy, but a combination of lawn moss killer and proper conditions will make it go for good.


If you really want to kill the moss in your garden or lawn, there’s one surefire way to make that happen. Break up compacted soil, apply lawn moss killer (and water it), treat acidic soil, and reduce shade – you’ll see the moss disappear within weeks.

Alternatively, encourage acidic and compacted soil to see moss spring forth like the spongey, delicate plant it is. I personally love the fairytale-like look it brings to a garden, so you won’t see me killing mine any time soon, but if you want to, now you can!