Peppers can be finicky. Too hot (above 90), too cold (below 60), too humid or too dry and they won't pollinate, leading to flower drop.
They are self pollinating like tomatoes, though, so I like to give our plants a little shake when I check on them to help with higher fertilizing and fruit set.
Finicky indeed. I started to shake up the flowers gently a couple weeks ago. I moved them into more shaded areas so as they're not in the blazing sun at the hottest part of the day. I'm seeing growth in some and not so much in others. It's a learning experience.
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