With the fluctuating temperatures this winter and the rather mild temperatures at night, I decided to try growing lettuce in a cold greenhouse. This is an experiment to see if I can actually get a nice headstart on a harvest.
I am experimenting with the same varieties of lettuce and the same amount of nutrients. I have one hydroponic tub in my seed room under lights that has a constant temperature of around 70°F.
The other tub is outside with natural light and a fish thermometer set at 65° F to keep the water from freezing. Other than the water heater, the greenhouse does not have any nighttime heat other than what the sun created during the day.
I have used a mix of Masterblend fertilizer, calcium nitrate, and magnesium sulfate at a 4-18-38 ratio. I measured it carefully to suit the amount of water that my tubs hold which is a bit over 4 gallons. The tubs are food-grade safe and used in restaurants so I am satisfied with my container choice.
I did have to shade the seedlings for the first day as the sun was very hot and I had just removed them from their soil. I did not want them to struggle to get settled in more than necessary.
Preparation
The first step was to remove most of the soil from the Red Leaf Lettuce and the Buttercrunch variety. I teased out the soil and placed them into a bowl of tepid water to keep them hydrated.
Below you can see how I carefully place the tender roots inside the foam tubes and cover the opening with the wedge to hold it in place.
I made these foam inserts out of a long pool noodle that you can purchase at your local dollar store. I just cut them to size with a serrated bread knife and used scissors to cut out a wedge.
You can see that I used a styrofoam board from the local hardware store. I just cut the holes with a hole saw attached to a drill to the size needed. This was a very reasonable way to get the project started. I actually made these last spring and had a very successful season growing the greens using the "Kratky Method".
This method does not require anything other than light, nutrients, water, and plants. As the water level decreases the plant's roots continue to grow due to the increase in the oxygen above the surface of the water. There is no need to add more water when the levels go down unless, of course, you are still not ready to harvest. Then, I would only add a small amount to keep nourishing the roots.
The above photo was taken last year when I first attempted growing without soil. I did end up with a wonderful harvest and I really like knowing what went into growing it myself.
I will do an update next week after we get through the next 10 days of freezing temperatures. I am hoping that the lettuce in the greenhouse will survive my experiment. The ones growing in the seed room are already doing very well.
Until next time, this is Sunscape
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