No, radon is more an issue in a basement with no air flow, where the gas can accumulate. A greenhouse will have plenty of air flow so radon would be no more an issue than if you were standing outside.
The holy trinity of wholesomeness: Fred Rogers - be kind to others; Steve Irwin - be kind to animals; Bob Ross - be kind to yourself
Yes, of course, and I accept that blame. In fact, i covet that blame. As does this tiny ad:
Permaculture Voices 1, 2 and 3 - all 117 hours of video!