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It’s Winter. Lettuce Eat!

February 10, 2012 Tags: , , Blog No comments

Lettuce is one of my favorite leaf greens to grow in my garden.  It is also one of the easiest crops that I grow.  The hardest thing about growing loose leaf lettuce in our area is keeping them cut back on a regular basis before they get bitter, and keeping them from bolting in hot summer weather.  This year, I have added a small challenge to growing lettuce in my garden… Growing it in the winter!  I decided to design and construct a lettuce box to grow fresh salad for consistent use throughout the winter.

Lettuce culture:

Lactuca sativa is a cool-season crop and develops best in cool, moist conditions (spring and fall in this area).  Lettuce will tolerate a light frost, but will not withstand below freezing temperatures in harsh winters.  Temperatures between 45F and 65F are ideal for growing lettuce, where temperatures above 65F would be ideal for growing warm season crops such as Tomatoes, Peppers, Squash, etc.

There are four types of lettuce: 1) Crisphead, 2) Butterhead, 3) Romain and 4) Leaf Lettuce.  Crisphead has a tight, firm head of crisp, light-green leaves.  Butterhead lettuce has smaller, softer heads of loosely folded leaves.  Romaine lettuce forms upright, cylindrical heads of tightly folded leaves.  Leaf lettuce has an open growth and forms many smaller leaves.  Leaf lettuce is the easiest to grow.

Goal:  Provide a growing space to grow lettuces and other cool-season greens. Create a space which is protected from heavy frost and from freezing winter season temperatures so that a freshly harvested, organic salad may be enjoyed year-round.

I started with a few basic sketches and measurements to get an idea of what I wanted.  I already knew the location where I would place the box.  I also know that I needed to keep the box elevated and under three feet deep, so that it was easy to work in when sowing and harvesting the lettuce.

After  hours of research and drawing more-detailed sketches, I had a game plan.  I then started calculating my materials and the cost to build the box.  One day I went to Lowe’s with my fiancé, Jessica.  Materials used for the custom-built lettuce box include:

  • (4) sheets of plywood
  • (8) 2×4” pressure treated
  • (20) ft of 1 ¼” wide foam stripping
  • (4) door hinges
  • (2) latches
  • (2) recycled, single pane glass windows, 3’x2’
  • (4) sheets of ½” insulation
  • (1) can of expandable foam insulation
  • (1) sheet of 4 mm plastic, 10’x25’
  • (1) 24′, 84 watt soil heating cable
  • (1) 4′ T5 fluorescent grow light
  • (6) yards of oil cloth
  • Nails, screws and elbow grease!

Cost for supplies: $300.00

Let’s get started.  Thanks to my dad, I have been trained in carpentry and have developed those skills throughout my childhood.  First, I constructed the side walls.

Next I cut the 2×4 lumber for the front and back walls, and attached all walls together.  Nails guns are very handy, by the way!

Next I cut and nailed the plywood for the exterior walls.

I decided that I would insulate the walls between the sheets of plywood.

Using recycled windows from a house that my friends were flipping, I had the transparent top for the lettuce box.  Unfortunately, the glass windows were only single pane, so they were really thin.

Next, I put that box in its place!  I chose a South-facing wall where I could put the box up against the house.  Being closer to the house will increase the temperature for the box on cold winter days and will also decrease the amount of heat lost to winter wind.

Woah!  This cheap indoor/outdoor thermometer gives me a rough idea of the temperature inside and outside the box.  On a warmer, sunny day the temperature in the box got pretty high.  This was without soil inside the box.

I used a few pieces of insulation for the bottom of the box.  Then I lined it with plastic lining, 4x thick.

I used organic compost, broken down on our own property.  This compost was from our chicken & goat manure.  We use pine shavings and straw for the bedding in our barn.  In the summer, we mix in grass clippings to provide Nitrogen for the micro-organisms to break down the carbon materials in the mix.

I added about 8-10” of compost manure on the bottom.  The compost wasn’t completely broken down.  So, when the microbes continue breaking it down, it will create extra heat!  Then I added sterilized, soilless potting soil to the box.  I added about 8” of this.  I bought a frozen bag of soil, so I had to let it thaw out a few days, since the temperature was below freezing that week.  I installed an 84 watt soil-heating cable into the potting soil.  I used this to keep the soil temperature around just under 70F degrees.

I needed adequate lighting in my box, since the light levels are already low in the winter.  I tried to angle the windows as close to 45 degrees as I could.  The angle of the sun is around 38 degrees in the winter time.  Where it is around 68 degrees high in the summer!  Anyway, the aluminum foil was used to reflect light rays, increasing plant growth.

Look!  It’s green!  I started seeds indoors under a high intensity fluorescent light a few weeks before I completed the lettuce box.  I purchased a 4’ long T5 fluorescent growing light for extra lighting on cloudy days and after daylight hours.

A few trash bags used to waterproof the outside of the box from excessive water damage.  I also applied oil cloth, 7mm clear plastic to the windows for more insulation.  The heat will have a harder time escaping the box when it gets trapped in the 1” area between the glass and the cloth.

Things are coming along.  I sowed another succession of loose leaf lettuce.

My thermometer showing the difference in temperature!  On sunning days above 40F degrees I open both windows all of the way.

When I thought I was going to harvest in a few days, something bad happened.  I went away, thinking that someone was going to keep an eye on my babies and open the windows when it was sunny out!  They didn’t open the windows!  But, it’s okay.  Lettuce grows quickly and it’s still an experiment at this point.

I will plan to grow lettuce from mid-October to mid-March this next fall-spring season.  I got a late start on the project this year.  From mid-March to early May I will most likely grow my other vegetable transplants and tender crops in this cold frame until the frost-free date (May 15).

As stated before, this was an experiment.  Below are some problems or things I would consider changing next time.

Goal:  Provide a growing space to grow lettuces and other cool-season greens. Create a space which is protected from heavy frost and from freezing winter season temperatures so that a freshly harvested, organic salad may be enjoyed year-round.

Some Problems:

  • Single pane glass was too thin: Water would sometimes freeze on the inside of the glass.
  • A late start: this next year, I will try to plant established lettuce plants in the box so they grow quicker
  • Would recommend building a lettuce box partially underground for more-consistent soil temperature and protection from extreme cold temperatures.
  • Make a written schedule with guidelines that are easy to follow so people know to open the windows when it is sunny out!

That’s all on the lettuce folks!

We received about 1″ of snow yesterday… And several thousand snow geese at Middle Creek Wildlife Refuge!  Check it out!


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