It is hard to predict which plants will survive and which ones won't because we don't know how pre-conditioned to cold they were, nor do we know how low the temperatures went or for how long. All of those play a role in what survives and bounces back versus what maybe seems like it survived but then just slowly fades away and dies.

If you had been having gradually colder nights before this big cold spell arrived and if your plants already had been exposed to temperatures at and below freezing, they are somewhat preconditioned to the cold and the chance that they will survive is greater. However, if y'all had stayed very warm and then they suddenly got slammed by temperatures that are far below average and far below what they've already been exposed to so far this autumn, the odds they will bounce back are slimmer.

Warm-season plants like your tomato plant will have a hard time bouncing back if they were exposed to air temperatures below 28 degrees for a substantial period of time. I've had some tomato plants in the greenhouse survive when the outside temperatures were in the teens and the greenhouse temperatures were barely below freezing, but those tomato plants were under a double layer of a heavy duty row cover. I should emphasize that tomato plants exposed to such cold temperatures usually stop flowering and setting fruit, but often will slowly (very slowly) ripen the fruit already on the plant when the cold weather arrives even if they are covered up well enough for them to survive. Sometimes the fruit doesn't get any larger though.Generally, once the plants are exposed to temperatures below 55 degrees, even if you keep them alive they produce poorly if at all. Peppers are the same way. Even before I had a greenhouse I could overwinter them in the garage, dragging the pots outside into the sun by day and back into the garage at night, but the fruit they had on them enlarged so slowly and ripened so slowly it really wasn't even worth the effort.

Collards, if pre-conditioned to the cold, generally survive temperatures down to the single digits----maybe 5 degrees or so. I have had them damaged by temperatures in the teen, but they bounced back and put out new growth once more moderate temperatures returned.

Pea vines likely will bloom if they are healthy enough that they continue to make new growth. They are fairly cold hardy. Often, even after the tips of the plants have been frozen, or after extreme cold has literally knocked blooms off the plants, they'll bounce back with new growth, new blooms and new pea pods.

Petunias are pretty cold-hardy. I have had them survive until almost New Year's some years, depending on the location they are in. Some times the ones in more sheltered areas survive and the ones in more exposed areas don't.

I usually have happy fall garden plants until they encounter nights in the low teens (uncovered). If I cover them with a heavy-duty row cover on the colder nights, they can withstand temperatures at least as low as 10-18 degrees that normally freezes them if they are uncovered.

I've never covered collards, spinach or kale and they rarely freeze, often surviving the entire winter in the ground with me harvesting the outer leaves continually. Keep in mind, I'm in zone 7b so our lows some years rarely dip below 10 degrees. I've lost uncovered lettuce at 18 degrees, so try to remember to cover it up if we are expected to go below 20 degrees.

Broccoli and brussels sprouts that haven't flowered by now probably won't. Once they are exposed to very cold temperatures for about 10 days, they often just give you buttonheads (heads that are literally the size of a button). This occurs because the cold weather signals to them that their death from cold is imminent, so they valiantly try to set at least a few seeds to guarantee their species will survive even if these plants die. If you were, by chance, growing a winter sprouting broccoli instead of a heading broccoli, it should bounce back and produce sprouts just fine. I've had purple sprouting winter broccoli survive entire winters with only minimal covering on very cold nights.

You can Google and find lists of the temperatures that will freeze/kill cool-season or cold-season vegetables, but those are just general lists. Depending on pre-conditioning, it is possible to have plants perform better than those lists lead you to believe. If they are shorter and lower to the ground, that increases their chance of survival. If their roots and soil were moist and not dry, that can slightly increase their chance of survival. If they were mulched to keep the ground warmer, that can help them survive. If they have a southern exposure and nearby masonry walls or concrete driveways or walkways, that can increase their ability to survive. If you are looking at plants that are dark green or black or brown, wilted and droppy or withered, they are pretty unhappy and may not bounce back.

I always wait a few days and watch to see if they perk up. Sometimes plants that seem dead really aren't. Sometimes they sprout new growth from the ground. Sometimes they don't bounce back and just slowly die over the next few days.

Sometimes the "wild card" in the equation that helps plants survive temperatures you'd expect to kill them is snow. If you had snow before the temperatures dropped extremely low, it can serve as insulation and protect them.

I assume you got a lot colder in your part of OK than we got down here. I think the lowest temperature we had in this cold spell was 15 or 16 degrees, and my Swiss chard that is out in the garden survived that just fine. Lettuce in the unheated greenhouse looks great. The greenhouse only dropped below freezing (down to 31 degrees) one night and then dropped down just to 32 degrees last night. Some of the brugmansias inside the greenhouse have freeze-damaged foliage, but most winters that happens and then the damaged leaves drop off and new ones grow. Everything else in the greenhouse is fine, and most everything else in the garden that had survived previous cold temperatures down into the upper teens did freeze on Sunday night. I might see some herbs in the ground bounce back---some of the borage and catnip still had some green foliage this morning. Based on previous occasions though, that green often turns black in the next day or two.

Thanks Dawn. This is the first year for cold weather gardening for me. We went down to 14 last night. 15 the night before. We had a light snow Sunday. I have already gotten a pretty good broccoli harvest. I was hoping for side shoots. The brussells sprouts have been behind everything else all along. They were transplants and while you can see the buds, the plants aren't as big as the collards or broccoli and have never looked as healthy. I watered everything well Saturday.

I've been wondering if you should fertilize in winter, like a little fish emulsion on potted plants, or the brussells sprouts.

If I planted lettuce, spinach and chard in the green house now, would it grow or just wait till spring?

Amy,

You're welcome. Winter gardens are like Forest Gump's box of chocolates---you never know what you're going to get, and you can blame that on the weather.

If the broccoli plants don't go limp, you might get side shoots. Then again, you might not. With the weather warming up again and with rain forecast in the next few days, some plants might bounce back well that otherwise would not have recovered much if the weather had remained very cold.

Fall/winter gardens never really seem to be the same in any two years because of the erratic nature of the weather here in the middle of the continent where it can change on a dime. I've had a hard freeze knock the plants back really hard, even if they didn't die, as early as the very end of September (I think that was in 1999) and I've had plants survive pretty much the whole winter in other years (2012 was one of those winters). The most cold-hardy plants like collards and kale can tolerate all kinds of cold and snow most years so they are almost just about guaranteed to give you a harvest. Swiss chard will suffer freeze damage fairly often here in winter and even die back to the ground, but in my garden it often resprouts and starts making new growth again within just a few days of freezing....just as soon as we begin to warm up again.

With plants in the ground, I don't fertilize in the fall or winter. All I do is add a thin (about 1/2") layer of compost to the top of the beds after the fall plants are up and growing. Whenever it rains or whenever I water, the water will carry nutrients down into the soil to the plant roots. I feed the soil with compost and let the soil feed the plants.

With plants in containers, whether or not they benefit from fertilization in the greenhouse will depend on various factors including how warm the soil and air temperatures are. Once the greenhouse is pretty cool, I am not sure if nutrients from fertilizers are taken up well and used. I don't fertilize the plants in the greenhouse in the fall or winter unless they have poor color or slower growth than they should, and since I don't expect much winter growth from them, I rarely feel a need to fertilize them.

If you plant your fall and winter crops on time (anywhere from July through maybe October), they do their rapid growing in those earlier weeks and months, and by this late in the fall, you are mostly just harvesting from them. They will make some growth in cooler weather with lower light levels and less intense sunlight, but it won't be really rapid unless you are keeping the greenhouse really warm both day and night. The downside to fertilizing is that you run the risk of pushing the plants to put out a lot of new growth, and tender new growth can freeze really easily when a cold spell of freezing weather hits.

Once daylength (the number of hours of sunlight per day) drops below 10 hours a day, plant growth slows signficantly. I think that once you're getting less than 10 hours of sunlight per day, there really is not enough light energy available to push much plant growth so the plants kinda stall and just sit there. I think that in my garden, that really slow growth period is mostly only in December, and maybe a bit of early January. Right now, in my part of Oklahoma, our daylength is running around 10 hours 20 minutes, with sunrise just after 7 a.m. and sunset a little before 5:30 p.m. The daylength will drop a little every day until the winter equinox arrives and then it will begin to increase again.

I've never tried planting lettuce, spinach or Swiss chard from seed this late, so have no idea how quickly or slowly they will sprout. However, I had lettuce seedlings sprout in a container outdoors a couple of weeks ago. They resulted from me leaving the lettuce plants to go to seed for the finches back in the spring, and I guess the finches didn't eat all the seeds. I put annual flowers in those containers at some point, but the lettuce seed laid there quietly waiting for the right conditions for germination, which arrived here in early November. (I never would have tried planting lettuce as late as November, but now that I know the seeds will sprout then, I might try it some future year.) Those lettuce plants were about an inch tall in the planter when I moved it into the greenhouse late last week, and some of them are about two inches tall now, so they are still growing. They are pretty dense in some spots, so I need to thin them out a bit. The greenhouse is staying in the 30s or lower 40s at night, and gets up into the upper 80s on sunny days. It might only hit 60 degrees on a cloudy day, but lettuce is fine at that temperature. I could leave the doors and vents closed, and the greenhouse could hit 110 or higher even in winter on a sunny, warm winter day, but I open the vents and doors when the temperatures hit the 80s because I don't want for the lettuce to get too hot and to bolt. That statement reminds me that in a fairly small greenhouse, sometimes you have to choose. I learned in past years that if I kept the greenhouse as hot as I wanted it to be during the daytime to keep the tomato plants and pepper plants happy and ripening fruit, (the 90s during mid-day were ideal), then it was too hot for the lettuce and the lettuce would start to bolt. So, unless your greenhouse is large or is sectioned in half with a colder area and a warmer area, you likely will have to decide whether to focus more on keeping hot-season plants going or replacing them with cool-season plants.

If you have soil temperatures and air temperatures warm enough for the seeds to sprout, they will grow.....sometimes greens grow surprisingly fast. I am going to link Tom Clothier's database that shows the relationship between soil temperature and seed germination. You can look at it and see how long it takes to get seeds of a given vegetable to sprout at a given soil temperature, and maybe that will help you decide if it is worth your while to sow seeds this late.

Keep in mind that you could sprout your seedlings indoors (I leave my light shelf set up in the spare room year-round, so I can start seedlings indoors whenever I choose) in warmer temperatures and then transplant your seedlings into their permanent (well, permanent for a few weeks or months) location in the greenhouse. About the latest I've ever planted spinach is in late October or earliest November, and that was in the ground in a year warmer than this and it sprouted and grew just fine, though it grew fairly slowly. We still got a nice harvest from it. Sometimes spinach grown in the ground from a really late sowing holds its own in the cold but doesn't get really big in winter. However, as the temperatures grow warmer in spring it enlarges nicely and you get a great harvest. Variety selection is important for winter---for a late planting I'd use one of the spinach varieties that matures quickly to make up for the fact that everything grows slower in winter. In a greenhouse, I think the spinach will grow just fine once you get the seeds to sprout.

You also can grow microgreens, which you harvest and toss on salads while they are very small. To keep microgreens going all winter, you could sow a new batch every week.

Remember that you can harvest lettuce leaves at any size using the cut-and-come-again method, and baby lettuce leaves are wonderfully sweet and tender and a great addition to salads.

There's tons of cool- and cold-season veggie crops you can grow in the greenhouse (and some can be grown in the garden under row covers as well) and some might be new to you: claytonia (aka miner's lettuce), tatsoi (spoon mustard), mache' (corn salad), beet greens, cress, minutina, arugula and endive. You can keep lettuce interesting by planting mesclun mixes that have many varieties in one seed packet. I grow one from Bontanical Interests called "Valentine" because it has lots of lovely red varieties in it. Johnny's Select Seeds and Botanical Interests have tons of lovely mixes of greens, as do many other seed companies.

If you like to use greens for braising and in stir fries, you can grow other types of greens like kale, mizuna, pak choi, Swiss chard, etc. Many Oriental greens are great for braising and also are very cold tolerant.

With most greens, rather raised for salads or for braising/stir-frying, you can cut them off above the soil with a sharp knife and the plants will continually put out new growth. That allows multiple harvests from the same plants over the course of the autumn and winter. Even plants that seem to just set there in the cold and dreary December/January weather often are biding their time, and start making much more rapid growth as daylength increases again.

I don't know if you'd have any luck sowing them now, but in future years you can grow green onions/scallions, leeks, radishes and chives in the winter, either in the garden under low tunnels or in the greenhouse. If you want to try growing winter onions in the greenhouse (for green onions to use like scallions, not for bulbing onions), you can order onion plants from Dixondale. I believe they start delivery of winter onions in either November or December. Their shipping date would be on their website. I have perennial onions in the ground in the garden, so I don't plant green onions for fall, but I bet you could grow them in a greenhouse.

I haven't tried turnips or carrots in the greenhouse, but when I grow turnips in the ground for fall, I can harvest turnip greens over the course of the winter. Sometimes they have freeze damage, but I just cut off the frozen leaves and throw them on the compost pile (where wildlife will gobble them up overnight) and new leaves sprout almost immediately.

If you are interested in growing edible crops in the autumn and winter in either a greenhouse or in low tunnels, I'd like to suggest the best book on the topic that I've ever read. It is by Eliot Coleman and is titled "The Winter Harvest Handbook". He harvests a commercial crop all winter long in a winter climate much more harsh than ours and this book tells you everything you need to know.....and more. Because of his harsher climate, he gets less growth in the coldest months than we do, so it is even easier for us to grow in the winter here. Still, it is notable he refers to it as the winter "harvest" handbook, which is a clue that most of the growth occurs prior to winter, but then you get to harvest over the course of the winter.

Wanting to start seeds now in late autumn will be a little more challenging, but the only way to know how well it will work for you is to just go out there and try it.

Dawn

Here is a link that might be useful: Tom Clothier's Vegetable Seed Germination Data

Once again, thank you Dawn! I've got some of those winter greens on my things to try list. We have a salad table that sits next to the south side of the house with about 8 squaer feet of growing space for lettuce. We do the cut and come again thing with that and some lettuce among the brassica. But I notice they are slowing down and the oldest tray is stalled, I think it needs something to boost fertillity. All the tomatoes in the green house are toast, except for one. Maybe I will bring it inside, but really, it's gotten cold enough it may never recover. I may "wintersow" some things in the green house...cool weather crops that need a headstart to mature before the heat.