What’s Green, Slippery and Dangerous?

That could be the start of a kid’s playground joke. If it is I cannot find the punchline. Actually, it’s not a joke, it’s something that can have quite serious consequences.

Carpet of moss on pavement and cycle path

In my picture you’ll see green stuff on the red tarmac that will be very familiar to you if you live somewhere where the climate turns cool and damp. It is of course, moss. We see moss every year on roofs of buildings, on patios, on stone or brick paths and on driveways. Mainly the moss is growing on areas that do not get much sun which fits in with this article from the The Royal Horticultural Society. From reading the RHS article the green stuff can also be algae, lichens or liverworts. One thing they all have in common is a need for moisture.

Why dangerous?

Walking on this green carpet means that every step is cushioned by a layer of moisture and that reduces the friction needed for you to grip the pavement. Without this grip to the pavement you can slip and fall over. There is a website in the UK called “FixMyStreet” for people to report local problems and there are several reports about slipping and falls on moss covered pavements. Moss can hold up to twenty times its own weight of water. Such a high capacity for water retention is great if you are into hanging baskets of flowers but makes life squidgy underfoot!

Moss – A green carpet mystery

I was standing facing more or less south when I took my photo of the green pavement and cycle path. As you can see, this part of the road is open with no buildings or bushes or trees at the side of the road. Which obviously means the pavement is not in shade. According to the RHS article, moss, algae, lichens and liverworts prefer shade so how is it that the moss is growing so well on the pavement? My theory is that the moss has loved the weeks of cool wet weather that I talked about recently in my article Alphabet Weather. The relative humidity has rarely fallen below 80% over the past 6 weeks and often stayed up around 90% or higher. Of course, the skies have been grey and the daytimes dull, so with these conditions and lots of moisture the green carpet has grown. Strangely though, the pavement and cycle track just a few yards up the connecting roads don’t have anything like as much moss. There must be other factors at play…….

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Welcome to my world of moisture

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