At the beginning of last week here in southern North Carolina, the temperatures were in the 70s during the day and the upper 50s at night. Then, for three nights in a row, the lows were in the upper 20s. The below-freezing temps only lasted a few hours, but here’s the result. The beautiful Café Au Lait dahlia I featured in last week’s blog had withered to a dark, dry, pitiful husk of its former self.
And as I looked around the garden, there were many more pitiful sights. I’d expected to see the volunteer tomatoes (I’d cleared the bed a few weeks ago, but I left the volunteers which had popped up elsewhere to see how far they’d get), the basil, the peppers, lantana, and zinnias to be finished, but there were a few surprises.
The yellow spider mums had been glorious, and I didn’t expect any damage to them or the other chrysanthemums. After the frosts, the foliage was fine, but the outer petals had turned brown, spoiling every single blossom. I’d intended to pick a spectacular bouquet, but so much for that! And about half of the other mums which were currently in bloom suffered the same fate. I was so surprised! I’d grown mums for years back in the northern California foothills with no problems. That was horticultural zone 9, and now I’m in zone 8. Doesn’t seem like that much of a difference, but maybe it is!
On the other hand, the violas planted over my dear rat’s grave (sweet little Francie) hadn’t missed a beat.
And the roses—even the new growth—were fine. By the way, the out-of-focus orange blob towards the upper right is a ladybug. And once I’d spotted her, I saw a bunch of aphids on the stem of one of the leaves. Those aphids didn’t freeze even though it seems by the look of them that their bodies my be 98% water!
For many years now I’ve seen similar sights in the garden after the first frost. But now I wondered why some plants succumb and other don’t. I don't know why I hadn't wondered before. I'd just accepted it - no questions asked!
The fundamental answer is fairly obvious. It depends on the climate in the plant’s native range. Plants have been acclimating to their native environments for a long, long time.
Of course, this is true for animals also, and some months ago I wrote about how mice had adapted to spend their winters in the subnivean zone. (You can find that post here https://www.kaarenpoole.com/post/comfy-in-the-subnivean-zone )
Mice are so cute—at least to me—but back to plants.
If a plant is native to cold climates, it has developed adaptations to survive frosts and freezes. On the other hand, plants native to warm climates have not.
Growers have been hybridizing plants for not very long at all—a few centuries at most. And they’re breeding for bloom size and color, plant size and shape, fragrance, and probably a few other characteristics important to consumers. But they have no chance of breeding for surviving freezing temperatures. The mechanisms which plants use to protect themselves from cold, harsh climates are much more complicated than whether or not there are ruffles on the petals. As I found out, adaptations to freeze tolerance are deep in the plant structure and chemistry itself.
Plants native to environments with cold winters have different cell structures and they shed their more frost-sensitive parts before the first frost. And the liquid in them is more than just water. It’s a viscous sap which doesn’t freeze (think maple syrup) or has chemicals which protect the plants from the degenerative effects of freezing temperatures. These chemicals are called AFP, or antifreeze proteins.
So, it’s no surprise that my lantana, native to tropical zones of north and south America, succumbed to the frost. And its also not surprising that my chrysanthemums, native to cold areas of China and northeastern Europe, survived the frosts even though some of the flowers turned brown. And, as for mums, their foliage does die back and the plant goes into dormancy for the winter, an adaptation for many perennial plants native to cold areas.
There’s so much to learn. And the first lesson is that zone 8 and zone 9 are different. They have different low temperatures and different first and last frost dates. And just a few degrees difference in temperature or a few days difference when, in the growth cycle of the plant, frosts and freezes occur.
There’s always something to learn in the garden, and that’s why I love gardening even though it demands much of us gardeners, including occasional frustration and disappointment! Fortunately, we're a resilient bunch.