Your plants, plus carbon dioxide = AWESOME

silvertipgrizz

https://fifthseasongardening.com/regulating-carbon-dioxide

https://extension.okstate.edu/fact-sheets/greenhouse-carbon-dioxide-supplementation.html

https://soilsmatter.wordpress.com/2016/03/01/leaves-left-on-the-ground-really-become-soil/

dipat2005

@silvertipgrizz I used to put leaves from the yard on my garden and everything worked great. Thanks for the great sources.

Jens the Beekeeper

Interesting articles. One thing to add to the CO2 article is that not only humans exhale it if your greenhouse or tunnel is big enough you could keep chickens in it in a pen and have them heat and boost CO2 levels all at one.