On Second Thought
Okay, so it turns out there's just one slight flaw with enclosing the back patio with plastic sheeting for the benefit of the plants; namely, that the back of my house faces a direction from which the sun does not, strictly speaking, ever shine.
So what this means is that the back porch is now shrouded in impenetrable gloom, which it turns out is an environment generally contraindicated for plants. (Mushrooms aren't plants, they're a fungus. And I am not growing those, so don't even go suggesting that I am.)
It also gives you the uncanny impression, when you look out the kitchen window, that you have suddenly become a character in Stephen King's "The Mist," which frankly is not very high up on my list of movies I'd like to be a character in.
Being a character in a porno seems like it might be fun, though I've never seen one and actually I suspect it would just be really gross. Also, I hear the music and lighting are terrible. Never mind.
Anyway, it's time to go to Plan B: either rotate my house about 87 degrees to the north, which might raise some objections for the neighbors, not to mention the landlord, or build a greenhouse in the backyard. I don't think I have any other option.