Are you looking specifically for twitter-ers or are blogs and Yahoo groups of interest? I personally don't see how you're likely to find a lot of highly valuable tree info being tweeted. I only follow one blog (even that is only as time allows) that I find of much interest. Everyone once in a while some new idea pops up. I belong to a number of tree-related Yahoo groups. Sometimes there are interesting conversations, but most of the time I could just delete the emails and be no worse for it. The "daily digest" setting is somewhat helpful.

I'm looking for active botanical gardens and tree enthusiasts that post pics or give summaries of a particular interesting tree or shrub. Stuff like that.

What yahoo groups do you subscribe to?

The Yahoo "Quercus Trees" group is good. If you remember Guy, from a few years back on here, he and many other oak experts are regulars.

The "magnolia" Yahoo group is fairly good if you are into magnolias. All or most all of the who's who in the magnolia world are on there.

I used to belong to a few different Yahoo conifer groups. They were all just a complete waste. I think I still have one (just haven't got around to canceling it), but got rid of the rest. I think they went wrong by trying to spread the group out into about four different groups by expertise. In the long run, they all just seemed to eventually flop.

There are many, many other plant related Yahoo groups, but I think those are all the ones I belong to that are about trees.

MOBOT has a twitter. It might warn you when they are closed due to weather and about a few specials.

My favorite twitter ever to follow was serge the robot maid from the Caprica tv show. It gave out good background info. Even selfies from Katy Perry and other gals get old or seem annoying somehow when mixed in with other nonsense.

Here is a link that might be useful: Mobot twitter

The Garden Professors blog can have some interesting stuff sometimes. It's not so much about specific plants (most of the time) but usually covers horticultural concepts and studies.

Here is a link that might be useful: Garden Professors Blog