I was just perusing this forum and saw nobody replied...
Without much knowledge on greenhouses, I don't think there would be a problem at all using treated wood for the base/sides of a greenhouse. If the treated wood is part of the actual structure of where soil/plants will be growing, there could be issues.
HOWEVER! Like I said, I hardly have any knowledge on this... just what I would think...

I was just perusing this forum and saw nobody replied...
Without much knowledge on greenhouses, I don't think there would be a problem at all using treated wood for the base/sides of a greenhouse. If the treated wood is part of the actual structure of where soil/plants will be growing, there could be issues.
HOWEVER! Like I said, I hardly have any knowledge on this... just what I would think...

Do you know what type of treatment was done to the wood? There have been changes in treated wood over the years to make it safer but I don't know when the changes were made or how to tell. I also can't answer your question but identifying the treatment type could help others answer it.

See if the board still have the treatment tags on them (usually stapled to an end). if so it should state the type of treatment, and you can look that up regarding soil contact and plants.

Or if you know where you purchased the boards, you can check with them to find out what they were selling 5 years ago.

I have read that if a 10mm gap (about a third of an inch) is used to separate an aluminum greenhouse frame from pressure treated wood base it will not cause corrosion. I intended to put a redwood piece of lumber between the frame and the PT base. Any problems?