If you’re heading into the winter time, you might be thinking about which plants in your garden might need protection to survive the frost. The good news for mosses is that they actually do pretty well for themselves in the winter time.
Moss doesn’t need any special care in preparation for the winter. They can tolerate temperatures as low as -4 F (-20 C) and produce their own anti-freeze compounds to resist freezing. As long as the growing surface is free of leaves, snow, and ice, new moss can be planted in the fall and winter.
Let’s have a look at the science behind why moss is so resilient at low temperatures.
Can Moss Survive Winter?
As one of the oldest plants, moss is well-adapted to survive in the winter.
Moss is a C3 plant. The “C3” refers to one of three metabolic pathways for carbon fixation in photosynthesis.
As a C3 plant, moss thrives with moderate sunlight, moderate temperature, and plentiful water, all characteristic of winter weather.
More specifically, most mosses prefer temperatures near 60-70 F (15-20 C) and they are resistant to cold down to -4 F (-20 C), some as low as -16 F (-27 C). In fact, they can actually tolerate temperatures below their ideal range better than temperatures above their ideal range.
Compared to most other plants, mosses (and bryophytes, lichens, ferns, and fungi in general) are much more resistant to colder temperatures compared to many flowering plants as seen in the table below:
Even at temperatures as low as 23 F (-5 C), moss still has a net gain in photosynthesis.
Given its tolerance to low temperatures, moss doesn’t need any special preparation for winter weather. It’s already well-adapted to withstand colder temperatures.
In case you might be wondering if fall or winter is a good time to plant new moss, the answer is yes. Moss is perfectly capable of surviving and thriving in cold temperatures.
The only thing to watch for is where you are planting your moss. Since moss will need some time to anchor itself to its substrate, make sure that wherever you are planting your moss is free from snow, ice, and leaves.
Any loose debris underneath your moss can prevent its rhizoids from developing a solid anchor to the ground.
Can Mosses Survive Being Frozen?
As you might imagine, freezing causes a lot of problems for plant cells.
When water within plant cells start to freeze, ice crystals can poke holes in the cell membrane or warp the shape of the cell, causing solutes to leak out.
It turns out, moss is pretty resistant to freezing. There are even species of moss that live in the arctic tundra, where there are freezing temperatures and strong winds.
Mosses protect themselves from freezing by producing their own antifreeze. The antifreeze is made of abscisic acid and phenylpropanoids.
Abscisic acid (ABA) is found in many plants and is used primarily to slow plant growth. Slowing plant growth is important because any new growth will require a lot of water, nutrients, and sunlight, which is typically harder to come by in the wintertime.
Phenylpropanoids refer to a diverse group of organic compounds. While they serve a variety of functions, in this context they act as an antifreeze compound by lowering the freezing point of water. There’s even a patent out there that uses phenylpropanoids as one of the components of an antifreeze solution.
Even when moss does freeze, they do seem capable of bouncing back. In one study, researchers were able to restore a sample of moss that was frozen for 1500 years in permafrost.
How Does Moss Handle Snow?
Snow counterintuitively protects moss from the cold by providing some insulation from the cold air/wind, acting much like an actual blanket.
While snow is cold for us humans, temperatures reach only around 32 F (0 C) under the snow, which is well within what mosses can tolerate.
Although snow can completely cover up moss, light can still penetrate into the snow. Light penetration will actually improve as snow melts and water fills the spaces between snow crystals, kind of like making the snow more like a clear window and less like a foggy window.
The snow also acts as a source of water and nutrients for moss. As dust and dirt accumulate on the snow, water will also trickle down and reach the moss underneath as the snow melts, carrying along the nutrients with it.
Does Moss Go Dormant In Winter?
Unlike most plants, moss does not go dormant in the winter. Most species of moss will still perform photosynthesis at temperatures down to 23 F (-5 C).
Moss is well-adapted to survive at lower temperatures, but the same can’t be said for higher temperatures.
Dormancy in moss only occurs when moss is dehydrated, typically at temperatures above 77 F (25 C). Temperatures above 104 F (40 C) can be lethal.
At higher temperatures, it is no longer “profitable” for moss to perform photosynthesis because more water is lost than CO2 is gained (to put it simply). Under these conditions, moss will go into a dormant state and reduce photosynthesis to preserve water.
Since moss is a C3 plant and prefers to have plenty of water, it would much rather reserve photosynthesis for low to moderate temperatures.
The concept of CO2 and water tradeoff is called net photosynthetic gain–a measure of how much CO2 a plant gains in exchange for lost water.
Every time plants open their stomata to take in CO2, a little bit of water escapes, even more so at higher temperatures.
If you look at table 1 earlier in this article, you’ll see that the upper limits of photosynthetic gain for mosses start to cap off around 30C (86 F). It’s around these temperatures where moss will start going into a dormant state, although it can depend on overall moisture levels.
That’s not to say that once the thermometer reads 86 F, moss will become dormant. The temperature will have some variation depending on things like shade, humidity, sunlight intensity, and nearby water sources.
If you’re interested in reading more, I recommend checking out this article which goes in-depth into bryophyte behavior at low temperatures.
Hope this helps!