Factors that affect romaine growth in a cold frame.

Ah, the joys of gardening. What is supposed to be a relaxing hobby for most can be laborious if you are a compulsive person such as I am.

So, today’s topic will have to do with my previous article on growing romaine in small cold frames. The question is will I have enough time to bring small starts to maturity considering that it is now past the middle of September and time is a wasting.

In order to answer the question, I need to start with some assumptions and some observations. The first is the time it will take for my small starts to mature. That’s an easy one as the published figure is about 65 days. Therefore from the planting in mid September I have until let’s say the end of November to get them grown. That comes to about 75 days, so at least I know what my target is. That is no longer than the end of November.

Next, I want to examine the major factors that will influence plant growth; length of day or sunlight, angle of sunlight or intensity and lastly the ambient temperatures I can expect.

Length of Day

The first thing I wanted to figure out was just how much sun the plants would get. As it gets later in the fall the amount of sunlight decreases as the arc of the sun’s travel dips ever lower in the south. Here’s what I found

As you can see my location here in southwest Missouri only gets a little over twelve hours (12.2) of light at this time of year. By the end of October I’m down to 10.6 hours and then as the end of November arrives my plants will only have 9.7 hours. The times are from official sunrise to sunset, so the actual usable times are much shorter. That is why it is so important to get time your romaine starts begun in such a manner that you hit the window of maturity right before it begin to get really cold which is mid December. (I’ve found that planting indoors anytime prior to the end of August seems to work).  By that time growth pretty much stops and yet the plants don’t seem to age if protected properly. That is as long as you maintain a temperature of at least the low forties in the interior of the frames themselves. I’ve accomplished this over the last couple of winters by using a small forty watt light bulb on a timer and then covering the frames with blankets whenever I knew it was going to get really bad outside. Perhaps surprisingly, whenever it has snowed, I’ve found I don’t need the lights or the blankets as the snow acts as a great insulator and the warmth coming up from the soil does the rest.

Angle of the Sun

The next consideration would the angle of the arc of the sun in your particular locale. The chart here shows how high the sun gets at particular from June through December at my latitude. As you can see, right now in September they’re enjoying pretty decent sunlight angles which can be also described as sun intensity. Too much intensity like I find in mid July will actually burn the plants up, while lesser intensity such as exists this time of year is optimal for growth. That seems to be true until about mid October when the angles begin to get pretty severe. On a side note, I decided for fun to verify that the sun’s angle at noon was a little over fifty degrees by quickly constructing the device you see here. It just a piece of cardboard with a circle drawn on it (I used a dish) and a thin length of metal punched through the middle. The angles I drew were on the rough side, but as you can see fairly accurate. Just make sure to align the board in a true north and south direction (use a compass) and insure the cardboard is level.

Temperatures

OK, so I have the feeling that I will have long enough days at good sun intensity for at least two more months. But what about the temperatures? I would like to keep the frames open as much as possible. Well, according to data taken from last year (2009) that should not be a problem. The graph represents the actual reading taken by a local weather station just a few miles from my home. The blue line represents 32 degrees or freezing. However, that is not really a problem with romaine as it has actually survived temperatures as low as 27F in previous years outdoors. So, assuming this graph of highs and lows is pretty close to what I can expect for 2010, then I should be good to go.

So that’s the plan Jan. I will do some updates as the season progresses. If everything works out, I hope to have a picture of me enjoying some fresh lettuce out of the garden on New Years Day 2011.