Thursday, January 23, 2014
The photo above shows you that I make mistakes and the consequence of one of them. This post is about that particular mistake, why I made it, and what I’ve learned from it that might help one of you someday.
We happened to be out of town the week that proved that the St. Louis metro region can still experience temperatures below 0F. In a previous post I discussed that the last time the temperature dropped that low at the official NWS weather station was in 1999, which seemed to put us in USDA climate Zone 7 rather than Zone 6 as is shown on the latest zone map. Being in Zone 7 would allow for a somewhat wider range of plants to grow here than being in Zone 6 does. On the other hand, I didn’t discount the possibility that we could again see temperatures falling below zero F. Good thing. For about 30 hours, from about 2 a.m. on January 6 through about 8 a.m. on January 7, the hourly temperature data points were all at or below 0F. The official low was -8F. It may have been a degree or two cooler at our house; it often is.
Before we left home the potential for this kind of cold spell had become clear. It presented me with a dilemma. I wasn’t concerned about the plants outside, even the tea plants, because we were also predicted to receive several inches of snow, enough to cover them and thus insulate them from the worst of the cold. All the outdoor plantings I currently have can withstand Zone 6 conditions. It was the plants on the glassed-in, south-facing front porch that I worried about, especially the frost-sensitive plants like the geraniums and the clivia. The glassed-in porch on our previous house had dropped below 20F when the outside temperature dropped below 0F. I thought it possible that this porch could do so as well. Temperatures that cold could kill the clivia and geraniums and possibly harm the citrus trees as well. Should I bring those plants in the house where they would be safe as long as the electricity stayed on, but which would be difficult in some cases due to their size and weight? Bringing them inside would mean I’d have to leave them inside till March because they would lose their adaptation to the slightly-below-freezing conditions they had already withstood and could reoccur. Plus we did not have enough available sunny window space for the geraniums, and the citrus would have to be kept on the floor of the guest bedroom, keeping us from using that space. Or should I leave the plants on the porch, risking their deaths, but saving a lot of effort and giving me a good test of just how hardy they might be? I opted for the second approach except in one case: I brought the smaller of the two clivia plants inside the house. This clivia grew from a seed from the larger, nearly 20 year old mother plant. It’s small enough to keep inside the house the rest of the winter, and it provided insurance in case the mother plant died. Before we left, I moved the flats of lettuces as well as the satsuma tangerine, the Bearss lime, and the hanging basket of begonias on top of the east row of 55 gallon drums, then covered the drums and the plants on the floor next to the drums with row cover. On the west side of the porch, I draped old sheets over the clivia and the larger citrus plants. The clivia sits on one of the 55 gallon drums, the citrus plants between the drums and the west window. I hoped that freezing water might provide just enough heat to keep that clivia alive and keep the temperature around the citrus plants within a range they could withstand.
When we returned home, as soon as I opened the porch door I smelled frozen leaves. Uncovering the plants confirmed what my nose told me. Both florist geraniums and the rose geranium were dead. The photo at the top shows the frozen clivia leaves. Most of the Bearss lime leaves were curled up and brown; the Meyer lemon and navel orange leaves were still green but curled up. Looking at the maximum-minimum thermometer, I discovered that the temperature had dropped to 18F at one point. It was probably colder near the floor. No wonder the geraniums died and the clivia froze. I hadn’t realized the porch could get that cold.
However, there were some pleasant surprises as well. The young satsuma tangerine, purchased just a few months ago, looked as good as ever, as did the lettuces and dill. The kumquat appeared to be mostly undamaged. The tea plant on the porch as well as the tea plants outside show no damage. Most astonishing of all, while the tops of the begonia plants on the porch frosted, the new leaves below them appear undamaged.
Thinking over what happened, I realize that I need to alter what kinds of plants I can keep on the porch if I want to leave them there all winter long. Citrus plants like satsuma and kumquat that can take temperatures around 18 to 20F are fine to leave out all winter long if they are covered during the coldest weather. However, Bearss lime is rated hardy only to 28F. I’ll have to bring it, or its replacement if it dies, into the house during the coldest part of winter. As for the clivia, I think the best thing is to keep a smaller replacement plant going once the mother plant gets so large I no longer want to move it. (The mother plant may not be dead -- its base looks OK under the wilted leaves -- but time will tell.) I plan to purchase a replacement for the rose geranium, but I’ll make certain to leave a space inside for it during the coldest part of the winter. I’m also looking into other plants that can take temperatures into the teens that might be candidates for life on the porch.
Another possibility is to better shield the plants from cold weather. Row cover works better than old sheets to protect plants; I’ll get some more of it. Covering the windows as well as using the row cover would also slow heat loss, and I will be looking into what might be available.
Heating the porch on the coldest nights enough to keep it just above freezing would be another option, but I don’t plan to do that. I don’t want to spend the money or be responsible for the attendant pollution. Keeping plants on the porch only makes sense to me if they can stand the conditions the porch offers them.