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Snow Mould

March snowmelt marks the welcomed advance of spring on PEI, but for about one in five people it also means the return of far-less-popular seasonal allergies. While you may be tempted to blame plant pollen for your symptoms, this early in the year the culprit is more likely to be right under your feet: Snow Mould.

Photo: Snow mould marks the transition from winter to spring on PEI.

Snow Mould is the cobwebby fungus you find on lawns and grassy fields in early spring. It thrives during the ‘vernal window’: that period between when snow starts to melt and everything greens up. Ideal temperatures for Snow Mould are between 0C and 7C (32F to 45F), making it a ‘psychrophile’: an organism that thrives when the thermometer is below 10C.  (We may not give them much thought, but many organisms – including Snow Algae that create amazing red, orange, or green snowpacks in alpine and polar regions – are psychrophiles. You know not to eat yellow snow but avoid the other colours too! Snow Algae are toxic).


Although it might look like it’s the snow that produces the mould, that’s not the case. Snow Mould starts to grow on dead leaves, longer grasses, and damp soil in fall. All winter, it continues to grow and infect new areas under the protective, insulating cover of snow. As temperatures warm and snow melts in the spring, Snow Mould gets active and spores become airborne. Unfortunately for allergy sufferers, those spores can cause itchy, burning, watery eyes, sneezing and coughing, and runny noses or sore throats. If you have “hay fever” in early spring – before there’s much tree or grass pollen around – Snow Mould is the likely culprit.


Fortunately, the Snow Mould season is short, and this particular form doesn’t do any long-term damage to plants. Normally, only the above-ground parts of grasses will be killed, and they’ll quickly regenerate from the roots. As spring progresses, wind will dry up Snow Mould and rain will wash the residue away. Rising temperatures will cause Snow Mould to go dormant for the summer, but it never goes away entirely. Like The Terminator, it’ll be back!


We live in the cold, bright, and noisy winter world above the snow and don’t often give much though to what’s underneath.  Down there is a cozy and quiet place called the subnivean environment that’s surprisingly important and home to many interesting parts of PEI untamed!

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