Procedures for protecting plants, and people, from the cold
Anne: November. Time for a report from the Craven Center for Applied Research. The fall/winter garden is beginning to look good. We have transplanted our tomatoes and the three kinds of Chinese vegetables. Crimson clover seeds are beginning to sprout where we want a winter cover crop. The pole bean vines that started bearing last June are still producing enough fruit for the Craven family dinner table; during the very hot weather they flowered but didn’t produce fruit because the pollen couldn’t survive the heat. The blackberry and muscadine vines are growing like mad; next year’s crop should be good. Now for Leon’s report.
Leon: We old-timers used to believe that late November would bring a few light frosts, December would be cool but not cold, and January and February would have several hard freezes that would hit the insect populations hard enough for a pretty good growing season.
But what can we predict now? Will climate change give us another mild winter? I don’t know enough about global warming to even make a comment. I do know that the weather has always been unpredictable. The last few winters have been mild, but short-range trends can be deceptive.
Accepting that we can’t predict the weather, I want to remind us all—working gardeners and arm chair gardeners alike—that we can have very cold weather down here in the South. Much of the material I am using this month comes from an article that Ed, my fellow horticulture professor emeritus and longtime collaborator, and I wrote back in 2003; but it is still very timely. We should not tempt fate by pretending that we now live in the tropics.
So, what should you do when the weather forecast is for bitter cold? Some plants come right through freezes and keep on blooming—pansies, for instance. I used the pansies outside our kitchen as an indicator of how cold the night was. If they rolled up into hard balls, I knew it got below 28 degrees F. Impatiens and coleus plants are killed by the first frost if they are out in the open; under trees they might make it through a few more cold nights. The more tropical plants, such as sansevieria and pineapple, will develop sunken whitish spots on the leaves if the temperature hits the low 40s.
When I started this article I thought it should include just a bit about the basics of cold injury. I tried, with a short tale about radiated versus reflected heat, frost damage, and wind freeze. It took up most of the allotted space. So, I refer you to the book that Ed and I wrote: Gardening in the Humid South. It has a chapter, “Three Dog Nights,” which describes the tricky aspects of our cold weather. With Christmas coming on, maybe you should get a copy for your spouse.
Here are some thoughts on how to protect sensitive plants. I will use citrus as the example; but cold is cold, and it will apply to all of your sensitive plants.
Satsuma is our most cold-tolerant citrus and can be grown anywhere in the Country Roads reading area. Navel oranges and grapefruit are a little more sensitive, but they can probably be grown as far north as Natchez. You can get one-year-old trees at your garden center and can expect to harvest a pretty good crop in about three years. With luck, you can expect three or four years of good harvest; but the time will come when you get a hard freeze, killing your citrus down to the rootstock. If the temperature is predicted to drop into the lower twenties, plan to cover the trunk with a dense mulch as high as you can. The key point here is to protect the tree to a little above the graft. If most of the tree is killed, but you still have living material above the rootstock, it will grow back during the next summer. If everything is dead but the rootstock, dig the thing up and start over.
What about draping sheets over the trees? That gives pretty good protection from a frost but is iffy for a hard freeze. Practically speaking, I think a cover of blankets will hold the ground heat in pretty well for one cold night. If this is a two- or three-day cold snap, you will need an extension cord and light bulb to produce some heat.
Ed used to put more emphasis on a windbreak on the northern side of the tree, plus a heat source. He used a kerosene lantern for heat; today you might choose an electric light. Some people will suggest that you use a water sprinkler. Don’t. It does work—sometimes—but my primary objection is the announcement you hear every time we have a hard freeze: “Don’t leave your faucets running all night. It will lower the water pressure making life harder for firefighters if a house is burning down.” Friends, that sprinkler uses a lot more water than a running faucet does.
Until a few years ago strawberry growers used sprinklers to protect flowers and small fruit, but they were pumping from their own wells. Now they use a material “row cover,” a polypropylene fiber, woven loosely so that it looks like the angel hair that is used on Christmas trees. This comes in rolls from about three to six feet in width. Because of the loose weave, it will insulate plants from the cold but doesn’t cause the covered plants to overheat when the sun is shining the next day. For sensitive plants in a bed, you can simply unroll a strip, anchor it with a few bricks, and leave it until the cold snap is over. With larger plants, such as citrus, you will probably need some sort of framework on which to drape the fabric. Most garden centers used to carry this row cover material—I hope they still do.
Now for a useless bit of fun. Back before central heating, we old-timers used to gauge the night temperature by the number of dogs needed per bed. Three-dog nights were about as cold as we expected the weather to get. But take a look at the formula below; it may help shed light on the science of this cold weather solution.
Anne: Sometimes, my husband and I are so focused on the plot of eight raised beds in one corner of our yard that we forget to look around at what else is happening in our backyard. Case in point: persimmons. I recently looked up into some tree branches to discover that the beautiful fruit was almost ready to eat. We have at least four persimmon trees scattered around the yard, but only two seem to be producing fruit. In any case, two persimmon trees are more than enough for us, and hopefully by the time you read this article in November we’ll be enjoying persimmon preserves, cakes, pies, sorbets, martinis, and more.
Leon’s assertion that “the time will come when you get a hard freeze, killing your citrus down to the rootstock” fills me with dread. Last winter was our first as owners of this backyard—which can otherwise be described as a mature citrus orchard. We ate and drank all we could, and still had boxes left over for friends and family. As a young (-ish) gardener, I just assumed that bounty would last forever. The day we have to dig up and start over will be a dark day indeed. Until then, we’ll have a stockpile of mulch at the ready.
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