@Seamaiden
He would keep his temps in the 70's w/ humidity with the ( Build your own DIY 5 gallon bucket no-ice evap air conditioner ) that I posted in this thread. Your product turns out much better in the perfect environment. I figured with only three plants for personal use he would want A+ .....
Would not really kill the electric bill adding this. Sure it will grow in the high temp's low humidity in summer but the product will suffer. Most the outdoor grown in cali has tons of extra leaf other issues because of the stress from high temp's and low humidity !!
I get your goals here, I really do, but an evaporative cooler isn't going to work very well, if at all, in his location. He's easily within 30 miles of the coast, which means he gets the marine layer that the SoCal coast is famous for. Here, it's even got its own Wiki page:
https://en.wikipedia.org/wiki/June_Gloom
(Now I've gotta look for the May gray page! July...? Sometimes it's a July fry, but often the marine layer sticks around well into August.)
Thank you for the detailed replies @Seamaiden. Your advice is really helping my understanding of growing some herbs, here :). I really appreciate it. I believe my main problem here is I'm simply overthinking it. I've seen videos of outdoor grows in Palm Springs, Mojave, Arizona, So. Colorado (basically az) and think about all the herb in Afghanistan, and Morocco, and places like that. DESERTS. All I have to do is what you said. Try to make sure the roots stay cool. I'm thinking about ditching the plastic around the greenhouse, NBD because it's cheap and I have more. I'm going to keep the pvc structure, and wrap it with some black, or green mesh to provide some shade for it, and then I may get a good layer of hay, or maybe mulch to throw on top of the soil to keep it cool underneath? I feel mulch would just bake, though, but I know it gets cooler a couple of inches down. I just need to get these out of seedling stage fast, and into my 5 gals with some of your plastic suggestion(would the paper get moldy?) And then they will be able to take the heat. You were right :). Not that I doubted you, I just needed to do more research into my desert like climate and growing herb in it. It's supposedly great for it, just need to raise these little girls up a bit so they can take the brutal beating. I've also heard that people get that water retention crystal nonsense that expand and they throw them in the soil and they absorb water and slow release as the soil dries, resulting in cooler soil.
Ditch the shade cloth, keep it on hand in case it gets really hot and you lose seedlings and have to start more. OR, use the shade cloth to shade the side of the house, because that stucco holds onto a lot of heat and reflects it back out, especially if that's a south-facing wall.
Keep the mulch layer thick and it's going to do a great job of maintaining moisture *and* keeping the soil cool. You can add those water crystal thingies, I haven't used them, my understanding is that how well they work is much a function of the soil itself.
Don't use hay, use straw. Hay will begin decomposing and cause you problems, straw won't do that for quite a while.
Paper on the outside of a pot or bucket doesn't really get moldy, IME. If it's got print on it, that will bleed off as you water, etc, no big deal. Don't forget the used soil bags here, they really work! I used to use old telephone wire to tie it around my pots, but anything will work. I just used what I had on hand.
