Cold Frame Plants

It’s been a couple of weeks since my last update on cold frame #1 (CF1). I have romaine lettuce, spinach and radishes growing here. As you can see by the picture of a spinach plant, the plants are getting bigger. Growth is not as fast as in the summer, but in view of the below normal temperatures we have had lately (daily temps in the 50’s and nightly in the 20’s) here in southwest Missouri, I am happy they are surviving at all. For added protection, I have made sure to place covers over the frames and even have rigged up two 40 watt light sources to help keep the internal temps in the high 40’s even when it has gotten as low as 24F.

The cooler growing environment is resulting in slower growth. That’s a given. What interests me, however, is the overall effect slow growth will have on the morphology of the mature plants. I do know that in very warm conditions, plants like lettuce and spinach will have a tendency to bolt. Bolting is very common in plants like these when they begin to form flowers and seeds in response to stresses like too much drought, light and heat. I am making sure to give my plants about an inch of water per week, light in the late fall and winter is now as severe and they are definitely not getting over heated. Even under full sun, with the lids closed, I am lucky to see internal temps in the mid 60’s. So when can I expect my first harvest? Perhaps sometime in late December. That’s my best guess at this point.

Internal cold Frame Temperature Data

After having constructed two identical cold frames and then planting vegetables in them. I began to think about what might happen if it got really cold this winter. I know that most lettuces and many cole crops (Broccoli, Brussels sprouts, cabbage, cauliflower, kale, collards, and kohlrabi) can survive brief bouts of freezing temperatures. What would happen, I wondered, if it got really cold out there. To that end, I decided to place two wireless 900 MHz temperature sensors into both cold frames just to monitor what was going on.

As luck would have it, last night it did get into the 20’s. I had the opportunity to graph both the ambient outdoor temperature and also the internal frame temps in 30 minute intervals. The graph above is a result of one of those experiments. Note: The Davis reading referrs to the outside ambient temperature.

The results were pretty interesting. For one thing, at 4:30 PM, I switched the sensors just to see if CF2 was really colder than CF1 and yes it is. That may be due t the fact that CF1 has a layer of plastic wrap over the glass which creates a small airspace that may indeed raise the insulating value a little. All other factors being equal, it may have increased the insulation enough to raise the internal temperature about 1 to 2 degrees.

The constant warmth of the ground also creates a warming effect as can be seen by the differing slopes of air temperature versus internal cold frame temperatures. I calculated that it will have to get down around 10 above zero before I would need to go to added measures like turning on an electric light bulb inside the frame. Some night if we do get exceptionally cold I will plan to stay up and record that event to see exactly what would happen.

Romaine is the Game

How can such a beautiful and healthy vegetable come from such a small seed? I choose to grow romaine lettuce in both my cold frames this winter for two reasons. One it is on the list of the American Cancer Research as a cancer fighting agent, and two it like cold weather and will mature inside of 60 days. It also does well in confined spaces needing just an 8 inch spacing between plants. Unlike leaf lettuce, romaine will also keep for long periods in the refrigerator and adds a lot of crunch to any salad.

Since I have about twelve square feet of growing space, I will be able to grow at least six plants in each cold frame while still having plenty of space for spinach and radish plants. By starting six new plants every third week, I will be insuring a steady supply of greens throughout the winter. Mind you, as a bachelor, I’m only feeding myself.

Got er Done!

Today was Sunday and it was nicer out than I had thought it would get. we started this morning at 27F but finished with the low fifties. The painting of the frame went quickly as did the did of the hole it would go in. I think the hole deal was about an hour or so. I have also equipped this frame with an internal wireless temperature sensor that is very closely matched to the one on the other frame. right now they bot are in close agreement with CF1 reading 55.4F and the newer CF2 reading 53.1F. As it turned out I did not have to purchase any vermiculite as by mistake, I bought three bags of Scott's Premium potting mix. This was a lot more money than I wanted to spend for this project, but since its done I went ahead and filled CF2 with 2 bags or 2 cubic feet of the stuff. I also have three trays of starter lettuce and spinach plants hardening off in the garage. I will plant these out into the new cold frame sometime early this coming week. The weather service is expecting temperatures to go on a roller coaster ride with cold fronts coming into our area every other day or so. I'm not too worried, however as early this morning when the temperature read a frigid 27F, the atmosphere in CF1 was a balmy 59F. I had covered it last night with two layers and made sure to leave the small 40 watt bulb on also.

CF2 on the Way!

It's now mid November 2008 and we are now entering the time of year I like the least. The next fourteen weeks will see some of the coldest weather of the year and most of the trees will be bare. Thank goodness for my cold frame with its spark of spring greenery inside. It will soon have a friend when I install a twin unit next to it. I'm in the process of painting the frame and still need to purchase a soil amendment (vermiculite)to add to the 3 cubic feet of Miracle Gro potting soil bought at a store last week. I now have three trays of plants (lettuce and spinach) that need to be planted out soon, so I need to get to it as they say. The new cold frame will be referred to as CF2 and the original CF1. CF1's plants are going great. I'll try and post a current picture sometime soon. The average temperature in that frame has been about 54F which is near the ideal temperature to grow lettuce and spinach at.

Over the next weeks they are forecasting a series of cold fronts about every other day with lows getting into the twenties. This will be a real test to see how well these guys can surviive.

Cold Frame #2

Yes, I’m at it again with the building of my second cold frame in less than a month. Does one man need two Cold Frames? Apparently, yes they do. Winter is coming and the price of lettuce at the local market is at an all time high. I love my salads (it’s a diet thing) and with lettuce at almost $2 per head, I now have plenty of incentive to grow my own.

The addition of a second 36 inch by 24 inch frame box will give me another 5.8 square feet of growing space. So, the two combined will allow me to grow about 12 to 14 plants at any one time. If I start 4 seeds every two weeks that will assure me a steady harvest of lettuce though out the wintertime and on into spring.

The construction will be documented in a video call Building a Cold Frame Part 2 and will be published on You Tube, I hope.

I had been concerned about the survival of young lettuce plants when it gets really cold outside. Recently we have seen temperatures that have dropped down to the low thirties and I am happy to report that conditions inside the box have remained in the fifty degree range. I have also installed an electric cord with a light bulb on one end to help warm things up in case it gets really cold outside.

Cold Frame Update