At the bottom of the newsletter, where it says ..... "Thank you for reading the All Things plants weekly newsletter. Had enough? Click here to unsubscribe."..... Is it possible to add something that would allow the reader to forward the newsletter to a friend?

Something like. "Click here to send this newsletter to a friend."

Just click the "Forward" button of your mail program.

That doesn't work for me. I don't use it. No problem. I'll copy paste the url into my yahoo mail.