Hi Mike, you're talking about a replacement for PVC clear greenhouse film, right?
I'm thinking a good approach could be to fit some glass windows or shower doors in an A frame over your "tiny" raised beds. Then you'd be re-purposing something instead of buying new.
"Hundreds of years from now it will not matter what my bank account was, the sort of house I lived in or the type of car I drove... But the world may be different because I did something so bafflingly crazy that it becomes a tourist destination"
If you have access to willow - almost any willow - they arch easily, and can be manipulated into all kinds of structures.
Edited to add: Oops! I misread. Have you thought about using fabric? Of course, that could get pricey, if you have very many, or they are very large. But, old sheets, yours or from good will, or other resale, individually, or sewn end to end...
The only thing...more expensive than education is ignorance.~Ben Franklin
Old windows with frames, if you can find them in a recycle place, single pane ought to be the cheapest, built into a squared-off hoop. They last for a very long time if you take care of the wooden frames, keep them stained, which seems to hold up better in the sun than paint.
The ends of the beds can be covered with shade cloth or shower curtains over chicken wire that can be raised and lowered.
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