Snow mold. What is it and how can I get it off my lawn?

I was actually going to title this post Snow Mold: Something to Sneeze At!  Or maybe Snow Mold: Gack!  What’s that Unsightly Stuff on My Lawn?  Way more dramatic and punchy, LOL.

I’ve been hearing over and over again how snow mold isn’t a “thing” outside of Canada (or even western Canada; I saw a comment on social media from someone in Ontario who had never heard of the stuff and I know they get snow there).  It’s quite possible that we’re more inclined to get it on the Prairies, as our winter conditions tend to support it more than elsewhere.  It’s not unusual to see the arrival of the white stuff before the ground is completely frozen, and then to have large accumulations linger throughout the entire winter.  This year, in Calgary (and it sounds like, in the rest of the province as well), we are having one big crazy snow mold party…it is everywhere!  Yay!  Achoo!

There are two main types of fungi that cause snow mold – gray mold is attributed to Typula spp. while Microdochium nivalis is responsible for pink mold.  You’ll instantly recognize snow mold because it flattens the grass and leaves a sort of pasty grey-white or pink-white webbing on top.  (You can see some good photos of it in this article). And you’ll also recognize that “snow” mold is a bit of a silly name, because the snow itself doesn’t actually mold.  It just acts as a cover for the fungal activity.

In the summer the fungi loll around and do absolutely nothing.  Although the heat doesn’t faze them, they are cold-lovers and when winter arrives, they get happy and start to grow.  After the big melt in spring, you’ll notice them clumping all your turfgrass together and looking mighty pleased with themselves.  And if you have seasonal allergies, boy, are you in for it.  Next to pollen, snow mold has got to be one of the worst triggers (just ask me, I know all about it).

So, will this icky grossness do permanent damage to my lawn?  Not usually. Severe infestations will cause patchiness, which can be easily remedied by overseeding.  To deal with snow mold, you can rake it really gently when the ground is dry enough to do so.  (If you have allergies, get someone else to do this job for you).  “Gently” is the operative word, here, as you’ll yank up your grass if you rake too hard this early in the season.  Bag up the clippings. Don’t thatch until later on, after the ground is completely thawed – this initial period right after melt isn’t the time to get aggressive with your lawn, as you’ll only do damage.  You can also choose to do nothing: as the grass dries out and the temperatures increase, the mold will become inactive again, and greening will happen on schedule.  A good soaking rain will also help wash away the problem. Don’t fertilize immediately after thaw, and don’t mow the lawn right away, either – wait until things dry up a bit.

Yes, snow mold will come back, and no, you can’t really do a lot to prevent it.  Rake up your leaves in the fall, and don’t use a high nitrogen fertilizer late in the season.  Give your lawn that final mow before the snow flies (if the precipitation doesn’t take you by surprise) – a shorter cut will also help deter voles, as well.


Further Reading:

Burke, Kelly. “Identifying and Controlling Snow Mold in Your Lawn.” The Spruce. February 2, 2020.



Snow mold: how to control it in your lawn.

Here it is:  the glass half-full.  As someone who suffers from intense hayfever, the cold, snowy weather and the subsequent setback of plants breaking dormancy has meant that it will be a good month or so yet before I start feeling poorly from the production of effusive amounts of pollen.

Now for the glass half-empty:  there seems to be an abundance of snow mold this year, lolling on lawns in the neighbourhood.  I’ve been sniffling and sneezing for nearly two weeks.  (Okay, I think I’m done whining now.  All expressions of sympathy can be directed to the “comments” section.  I’m big on sympathy).

So, what is snow mold and what can we do about it?  It does indeed look gross:  circular grey-white fuzzy stuff called mycelium matting all over the dormant grass.  It has a sinister quality, just lurking there on top of your lawn like a silent killing machine (not to mention, making some of us sick.  Did I mention the sneezing?).  Snow molds are fungi, and there are several different types:  the kind we probably have here in Calgary is a grey type called Typhula ishikariensis.  Fortunately, despite its appearance,  it’s not likely to cause any sort of permanent damage to turf, as it only affects leaf tissue.  (There is a pink snow mold called Fusarium nivale that can be deadly, as it destroys the crowns of plants affected.  Thankfully it’s not as common as grey snow mold).  Snow mold occurs whenever there is an extended period of snow cover on ground that is not solidly frozen.  The fungus actually lies dormant during the long, hot days of the summer, taking a siesta on the leaves of grasses as tiny black specks called sclerotia.   Any time you mow or walk across the lawn, these miniscule sclerotia go for a ride and gleefully spread, carried on your shoes or your dog’s paws or the mower blades.  Once the temperatures drop to the freezing mark in late fall, the sclerotia spring into action, germinating and producing thousands of spores.  Beneath the cozy blanket of winter snow, the fungus munches on dead organic matter and thrives until exposure in the spring.  (Snow mold cannot freeze because it manufactures special enzymes that keep it from doing so).

While there’s not much you can do about the fungus, as once it’s on the lawn, it’s pretty much taking up permanent residence, you can keep it from making a mess in the spring (and giving me sniffles).  Make sure you clean up all of your leaf litter in the fall, as the fungus holds dead leaves in the same high esteem as I would a gigantic hot fudge sundae.  And keep your lawn short – don’t forgo that last mowing of the season, and don’t leave clippings on the lawn after that final cut.  Don’t fertilize too late in the season, as a huge nitrogen spike at the wrong time can actually contribute to serious winter kill of your turf, and in less extreme cases, aid in the growth of snow mold.  And don’t walk on the lawns in the winter, if you can help it – even what seems to be slight compaction on top of the snow can motivate fungal production.  In late spring, it may be a good idea to spread the snow banks around, dispersing snow over the entire lawn to aid in a more “even” melt.

Even meticulous grooming might not prevent snow mold from rearing its ugly mycelium in the spring, but the fix is easy:  let it be.  No, seriously.  The fungus hates heat and drought and it will go dormant as the weather improves.  You can also rake the grass with a fine-tined tool and that will help immensely (but wear a mask if you don’t want to inhale the spores and sneeze repeatedly.  Like me).  I have also been told that you can use the high pressure setting on the nozzle on your garden hose and give the grass a good rinse – but do it when the day promises heat and drying winds.  If, for some reason, the lawn can’t recover from the effects of the mold, you will need to consider a prescription of topdressing and overseeding, but that’s a rare occurrence.

Glass half full:  snow mold means spring has arrived.  How fantastic is that?!


Dr. Tom Hsiang, a professor of the Department of Environmental Biology at the University of Guelph, has written some interesting stuff about snow mold at