George has left some comments that got me thinking again. Thus I'm still tinkering with the plastic bottle idea. Using bottle hotcaps has its pitfalls (too much heat). So do the collars (not enough wind protection). So I think.......could something half way in between work better? Thus my latest twist is the bottomless/topless bottle. These end up being a tall collar, twice as long as the original collars I made.
By removing the bottle top, the seedling won't overheat and bake to death.
By having tall sides, the seedling is protected from the drying wind, plus the air around it will be warmer and have more humidity than if it were unprotected. It will be somewhat of a greenhouse effect.
So in theory, these tall collar-like protectors should give better results than either the hotcap design or the short collar design. Now for the test.
I'm thinking that with some veggies, these tall collars can be left in place even as the plant keeps growing, such as with broccoli, chard, kale, tomatoes, and other tall growing plants. With shorter or spreading veggies, the tall collars would need to be replaced with a short collar before the seedling grew too large, such as with dwarf bok choy, cabbage, parsley, and such. If perchance these plastic collars keep most of the slugs off, then I'll use them on as many crops as possible. We'll see.
Now for some photos of results to date.......
We've been having sunny, windy days which have been brutal on the young seedlings. The ones protected by the bottle hotcaps have been doing fine. Those with no protectors are totally wilted, even though the soil is damp under the surface.
But even a short collar gave protection. Only the parts of the leaves above the collar rim have wilted. The rest of the seedling is fine. So it's the wind that's the main culprit.
This bed should have had all the bottle hotcaps put into place and then munched, but I was still searching for more bottles. Plus I was short on mulch. Dang. But it's nice to know that the bottle method has potential to be very beneficial.