Seed catalogs say “sweeter after a frost” when describing winter vegetables. It’s true. As I explained last week, vegetables like kale, Brussels sprouts, leeks, carrots and cabbage all taste sweeter after a frost or two. This characteristic of hardy vegetables is one of the many advantages of growing in the North.
Veggies sweetened by a freeze sounds like magic, but actually, it’s one of those charming aspects of nature. When the temperature dips below freezing, the air is moist enough for water vapor to condense in the form of ice crystals on the ground, as well as on the plants. Then, when the water condenses again, it actually gives off heat, warming the air around plants. This pocket of warm air creates a cozy microclimate that protects plants from extensive damage.
On the other hand, when temperature drops more than a few degrees below freezing, frost damage to leaves, tender shoots and flowers is more likely to occur no matter how humid the conditions are. That’s because water, whether in lakes, ice cube trays, or cells, expands when it freezes. So as water within plant cells freezes, it ruptures the cell walls like a water balloon bursting under pressure.
The sweetness comes from a plant’s physiological (a fancy word meaning the branch of biology dealing with the functions and activities of living organisms) response to cold temperatures. When temperatures fall, certain plants (especially members of the cabbage family) increase the amount of sugars and other substances in their cells. This sugar solution acts like antifreeze. It also makes many species taste much sweeter after they’ve been well frosted a number of times, which explains why many local berry pickers wait until after a frost to harvest their favorite late summer and fall berries.
For root crops like carrots, parsnips and turnips the additional sweetness happens because of a different process. The plants respond to cold by converting their starches to sugars. In the case of winter leeks, however, they go dormant during cold snaps. When temperatures rise again, they resume growth and become sweeter. So you can see how it pays off, flavor wise, to wait until fall has made its mark on your crops.
Now, that’s not the end of the story. Different plants and parts of plants have different freezing points. It’s a measure of frost hardiness. For example, pansy and nasturtium flowers might wilt at 31 degrees, while their leaves remain firm and undamaged. The next time we get a hard frost, take a walk around the yard or local trail.
Frost hardiness is important when purchasing plants and spring bulbs, and when sowing seeds for overwintering. Plants that are native to, or naturalized for, northern regions have built-in mechanisms to survive the cold. You see this adaptation at work each fall as the tops of perennials like columbine and rhubarb die back, while the roots and crowns which are buried in the insulating soil, remain alive to sprout again the next season — your reminder, dear readers, to apply a layer of mulch soon).
Beyond the garden gate, maples, mountain ash, cottonwoods and other deciduous trees have a protective plan, too. After dropping their leaves, trees form leaf buds that stay tightly wrapped within many layers, like mummies. These mini-mummies go dormant until next spring. Hardy plants like Sitka spruce trees also contain a natural anti-freeze in their sap that helps prevent them from cold injury.
Back to mulching: In the garden, one of the best defenses against freezing temps is to apply a 3- to 6-inch layer of mulch in the form of leaves, compost, seaweed (or a combination of all) around the base of shrubs, trees, and perennials. Distribute the mulch toward the trunk, but not up against it. For perennials, apply mulch on top of plants after the main plant dies back. At the very least, cover your perennials with spruce boughs which allow for good flow of air, light, and moisture.
• Last call for sowing spinach seeds for a late winter crop of greens.
• Weed: Get right on it or you’ll be sorry. (One year’s seeds can translate to seven years of weeds.)
• Harvest: You worked hard to grow the stuff, so don’t let your efforts go to waste. Divvy out extras to neighbors, shelters and food banks. One more thing: harvest with your kids and grandkids. What better way for them to learn where real food comes from?
• If you plan to overwinter begonias and dahlias, hold back watering them from now on to allow soil to dry out.
Gardeners of all experience levels are encouraged to join the Kodiak Growers Facebook page. To contact Marion, send her an email (firstname.lastname@example.org), or head over to Facebook, Instagram (marion_owen_photography.com) or her blog at marionowen.wordpress.com. Or pick up the phone, 907-486-5079.