by: Lucia Kearney
I have to admit, I’m a bit nervous for the winter. I grew up in and around Philadelphia; it was a big deal if the temperature got down into the teens, let alone the single digits. We’d get snow, to be sure, but it would usually melt within the week. Honestly, I’ve never really developed a tolerance to cold; I spent an awful lot of time by the wood-burning stove in wintertime back home.
When I knew we were moving to Minnesota, my first farmer instinct was to check the USDA zone. I blanched when I saw it: zone 4, average extreme lows between -25 and -30. Last year, I spent the winter back in PA, but this winter I’ll be working on the farm all the way through. This year, I’ll have to learn how to use long underwear and coveralls and patch up my winter boots.
But there’s one thing about the cold that I know will bring me happiness as I learn to weather the Minnesota cold, a phenomenon known as winter sweetening. Have you ever wondered why we don’t grow spinach in the summertime? Sure, it’s prone to bolting in the summer heat (that is, the heat makes the plant kick into its end of life cycle, putting all its energy into making flowers and seeds, leaving leaves small and bitter), but the real reason is winter sweetness.
It may seem like an old wives’ tale, that some vegetables get sweeter after a few frosts, but it’s a well-documented scientific phenomenon. While frost will kill your tender summer crops in one fell swoop (like tomatoes, cucumbers, and eggplant), cold-hardy plants will begin to produce more sugar. Why? Sugar helps the plant to withstand the cold.
Here’s how it works. During the process of photosynthesis, plants use light energy from the sun to transfer electrons from water molecules to CO2 molecules resulting in the production of carbohydrates and oxygen. Plants store their energy in these large carbohydrate chains (starches) during the warmer months. When the nights start to get cold, however, a defensive mechanism against frost kicks in. Cold-hardy plants – like spinach, broccoli, carrots, and kale – begin to break some of their starches down into smaller “free” sugars, like sucrose and fructose. These free sugars move into plant cells, thereby changing the overall composition of the fluid within the cells. Much like salt water has a lower freezing point than fresh water, the sugar in the cells works like anti-freeze, allowing the plants to withstand colder temperatures than their summer counterparts.
It’s this defense mechanism that makes winter spinach taste so much more delicious than spinach harvested in the summer ever could. And while kale and carrots taste just fine in the summertime, there’s nothing quite like candy carrots and Siberian kale harvested in the cold.
My hope is that maybe, just like spinach, I’ll benefit from the cold this year. That I’ll develop a tolerance to cold weather, a love for the snow, and that maybe, just maybe – with the help of shared dinner’s on the farm and the welcome greenery of the greenhouse – I’ll get just a little bit sweeter too.