Saturday, January 9, 2010

How Do Perennials Survive a Northern Winter?

While much of the nation sits in a deep freeze, here I am, in my nice warm family room, looking out at a sunny blue sky day. The ground is covered with snow (four inches of it), and the thermometer reads 9°. With temperatures like this, I'm glad we've got the snow cover, because it helps insulate the plants from the cold. 

Mulching helps keep roots warm, and I'm glad I added more to the base of some of the more tender plants this fall. But it's still pretty darn cold under that mulch and snow, and the ground is frozen solid.  How do the perennials live to see another spring?

Of course, some survive better than others. That's what the USDA hardiness zone ratings are for; a plant that's only hardy to my zone 5 won't make it in Alaska's zone 2. But the mechanism that allows a plant to return in the spring after a winter of below freezing temperatures is the same.

Many perennials lose the parts of their plants that are exposed as the temperatures drop.  The roots in the ground move as much of the the water in their tissue's cells into the surrounding ground as possible. With less moisture in the plant's cells, a certain amount of freezing and thawing can occur without rupturing those cells.

Also, sugars and salts in those roots act as a natural antifreeze. By lowering the freezing point of the water in the plant's cells, it allows them to survive lower temperatures. Think about what happens to ice and snow when you salt the sidewalks. It works much the same way in plants.

I'm not a botanist, but that's basically the gist of it. Pretty cool, huh?


Unknown said...

Cool indeed, Kylee. I don't mind when it gets cold if it would just STAY cold. What does things in here is the freeze/thaw cycle, which heaves plants up, especially if planted in last year or so. I mulch my hellebore and the fancier echinaceas with the cut up Christmas tree, and straw if needed, and that protects them. Other stuff is on its own.

Anonymous said...

Pretty cool, indeed...and thank goodness it is. :)

Lisa at Greenbow said...

You bet it is amazing that they survive. It looks like Romie had some fun with the snow blower in your garden making a path.

Nutty Gnome said...

I wondered how they did it!
I'm so hoping my plants are being proctecte from our severe temperatures by the large amount of snow on them! It's been well below 0 for about 10 days now, but we've got about 7inches of snow too. I guess I'll just have to wait until spring!
Stay warm :)

Teresa O said...

It is cool, Kylee! I learned something new today. I'm just glad that many of my favorite plants have the ability to withstand the onslaught of winter.

Gail said...

Cool, yes, cold, yes. I did not know that, I knew there was something magical about their survival.

Lona said...

I am so glad we have this snow cover too Kylee with the cold temps upon us. We have a foot accumulated now with all of the daily flakes adding to it here in the hills. We usually get a few more inches up on top than what the valley gets.
Stay in your warm family room and hot chocolate is in order. ;-)

Mr. McGregor's Daughter said...

Plants are nifty! We're lucky we have good snow cover, unlike our friends in more southerly climes whose gardens are having to deal with the cold with no protection. The year I lost the most plants wasn't the winter with the coldest temperatures, it was the one with no snow cover.

Unknown said...

Perennials are amazing! That's why I love em.

Jim Groble said...

Very cool indeed. I've always thought that my plants needed a snow cover, but I really never knew why. Now I do, outstanding! We finally saw the sun today after 5 days of snow. Your pic looks great.


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