Apparently it's forbidden to post a question on two forums at the same time, but I see that my hydrogels qustion post has been locked on the rose forum and this was the motivation given. However I posted a tree question on the tree forum and on Ask a Question and this was permitted. I don't understand...

It's not forbidden, I initially locked it as i thought you had accidently posted the same question twice (we see a lot of duplicate posts everywhere from returning members having their browsers resubmit their last posts in error!) Since it didn't seem rose related, I just added the link to the rose thread one, it kept the question there and any of the rose member that have additional input can go directly to the linked thread, thus keeping all responses in one place.
I unlocked the rose one, my mistake, having the link there is sufficient.

OH WOW -- I only thought you could do that on two-fer Tuesdays.

Bart, I noticed your double post, because I'd responded on the other thread, and when I saw it on Roses I thought for a minute my answer hadn't posted. Figured it out quickly, but that's one reason why double-posting causes confusion. Another reason is that sometimes responders build on each other's comments to further develop an answer or theory. Group problem-solving, so to speak. When there are two separate threads for the same question, that doesn't work well. So, not some arbitrary, pointless rule—it just makes things easier.

And others often post in more than one forum just to get it out to more members but also add a link to one thread just for the reasons posted above.

Thank you all so much. In future I'll try the link thing, because I did want to get it out to as many people as possible-but I very, very much wish to encourage the "group problem solving "approach; that is one of the principle reasons I post on these forums, lol. Sue, I do apologize for the fact that I put it on the rose forum without explaining; I guess the problem there is that I'm so into roses that I sometimes just forget that other people can't just "know" that automatically. In fact I am trying to expand out from roses; I've been adding trees and other shrubs, but my garden started out with roses and in a way they seem somehow to be part of it's backbone; it still amazes me that some roses do so well in my extremely difficult conditions, and some are actually easier to get "started" and established than trees.