January 9, 2012

Germination trials: low tunnel coverings

Once the PVC pipes were set up on the greenhouse benches it was time to cover them, creating mini-greenhouses.  This led to an introduction into the world of plasticulture.  Tons and tons of plastic is used to grow our food.  So much, that the word plasticulture is used to describe all the greenhouse coverings, drip irrigation, mulches, wind breaks, post harvest handling, marketing, and fertilization tools used to grow food crops.

There are a lot of different kinds, colors and weights of plastic to use when making a greenhouse, high tunnel or low tunnel.  Here are the four kinds of plastic we picked and one non-plastic treatment:

1. Sun Master 70% Opacity overwintering film

From it's name you can tell that not much light gets through this white polyethylene plastic.  It's the kind of plastic that is put over greenhouses or tunnels that house woody plants in the winter to keep temperatures within from fluctuating too much.  So, it should be "warm" inside which will promote seed germination, but it will not be good place for leafy plants to actually grow.

2. Sun Master Greenhouse Film 

This is the clear plastic that you would expect a greenhouse to be made out of.  It is 6mm thick polyethylene and allows a whopping 92% light transmission through.  So, this one should keep it "warm" inside as well as let plants grow because they will have some light.  (I say some light because all the layers of plastic add up.  If there are two layers of plastic on the greenhouse itself and one on the low tunnel only 78% of the available light can be transmitted through.  On a dark winter day that isn't much light.)

3. Agribon+ AG19 Row Cover

This is a agricultural fabric but it made from plastic as well.  Polyester and polypropylene strands are bonded together in a swirly random fashion resulting in the term "spunbonded".  This makes a cloth like covering that allows water through, but doesn't actually absorb water as a true cloth would.  Spunbonded fabric comes in a range of weights.  The one we're using allows an 85% light transmission and weighs 0.55 oz/yd.

4.  Clear plastic with holes in it

I haven't sourced this plastic so I don't know much about it yet.  It is far thinner than the other plastics we chose so presumably more light will be transmitted through.  It is also covered in holes which allows better air flow.

5. KEN-BAR agritape heat mats

These obviously are not a covering, but they are the final treatment in this experiment.  They still alter the plant's environment by keeping the soil and roots warm.  Heat mats come in all sorts of shapes and sizes.  This brand often is used by people who keep terrariums filled with snakes and other cold blooded animals that I wouldn't want to have for a pet.  Right now we have the heat mats set to be 40 degrees Fahrenheit at night.

6. Control

Every experiment needs a control.   I forgot to take a picture, so you'll just have to take my word for it that there is a bench with a bottom layer of plastic and nothing else.


  1. Wow man i never used to think about this this blog open my mind and I enjoyed this when I was reading this blog
    Keep it up man

  2. Thanks ~ I am glad you enjoyed it!