How to extend the growing season
The growing season of Chicago begins April 20th when the snow melts and ends the week before Halloween as temperatures dip below freezing. This estimate leaves us with 187 days of viable weather for food production. So how can we better utilize the 178 days of the year deemed ‘unfit’ for food production?
Below is a tutorial of the construction of a solar shelter/cold frame which took place in mid-February 2020 (over 60 days before the final frost). The materials needed to construct a cold frame can be almost entirely scavenged from alleyways. And if constructed properly, the microenvironment within these shelters allows for soil and air temperatures 20 degrees warmer than outside temperatures.
To keep heat and humidity within the shelter, it’s critical to eradicate the three forms of heat loss; conduction, convection, and radiation. To do this, our solar shelter will need 3 primary components;
- Structure – (Materials such as sticks, poles, etc)
- Light penetration/moisture retention – (Materials that allow light to pass freely and prevent evaporation. Most clear plastic containers, polyethylene sheeting etc.)
- Radiation reflection – (Materials that reflect light back onto the plants themselves. aluminized mylar, foil insulation, etc)
- Heat holding capacity – The best way to store heat is via water. Water acts as a battery for heat. It charges up throughout the day and releases at night. Even the water stored within plant cells helps store heat.
Let’s begin! Firstly, materials are sourced from local waste streams.
Next, a raised bed is chosen for a solar shelter. This particular bed has the greatest south-facing potential. (Most light)
The structure is a classic “A-frame” design consisting of sticks and cordage.
The aluminized mylar is placed on the north side to reflect sunlight entering from the south. Very little light comes from the north, so its best to keep its covered.
On goes the polyethylene sheet! This sheet will create a greenhouse effect, preventing moisture and heat from escaping. The plants will thank us later!
Time for planting! These lettuce seeds were germinated using a damp paper towel and plastic bottle. It’s best to germinate indoors where temperatures are higher.
The germinated seeds are planted. Ensure proper spacing and depth. Good rule of thumb, plant your seed depth to twice the width of the seed itself.
The plastic sheeting is sealed up and left alone. 2 months later, the lettuce has grown to adolescence! (10 days before last frost date.)
This solar shelter adds 120 days to Chicago’s 187-day growing season. What was once a 187-day season can now be a 307-day growing season. This means more locally produced food for more people.