First up, blotanical.com, "where garden blogs bloom".
Like most community/social sites, you get out what you put in; if you're not interacting with other members and their blogs, you're unlikely to become popular on the site - there are a few fellow orchid maniacs on the site - active amongst them are klaraau01 (My Orchids Journal), makarimi (Orchid de Dangau) and MM (Essence of Stanhopea). Whilst true gardeners are the focus of the site (and the majority of its users), specialised plant growers and indoor/balcony gardeners are also there. The community as a whole is quite welcoming of fellow plant enthusiasts - whatever their particular plant passion might be.
You'll spend quite a bit of time "picking" posts - blotanical's "favourite"/rating system, as well as messaging other users. It's important you do this when you first join in order to build your profile and become part of the community - and of course to carry on doing this over time! Blotanical also gives you an opportunity to see who has been "picking" your posts - handy to find users who also share your interests. You'll also find a lot of blotanical users commenting on your blog too.
You can of course search the site and its blogs, but you'll probably find it more interesting to browse geographically and find other users near you.
The only thing I find a huge drawback to the site is that it really breaks multi-tabbed browsing; if you try and visit a lot of different "plots" (blotanical's user profiles) or blogs within blotanical in many different tabs, it ultimately ends up setting all of them to the last one you happened to click on. I'm a big fan of opening a bunch of tabs, and letting them load whilst I get on with reading something else. With blotanical, you're best off interacting with the entire site through just one tab. Using blotanical is a bit like growing plants from seed - there's quite a lot of waiting involved. :) A futher slight niggle is that to get to your own "plot" if you've moved off it to another (which you inevitably will as "plots" are pretty key to the whole thing), you have to click on the currently active plot and then "return to my plot" - I think your own "plot" should always be in the navigation as a single click location.
On the whole, the navigation is a little unusual - I received many messages from members commenting on posts and then telling me to give them a shout if I got stuck on the site or couldn't figure it out - clearly it's not all that intuitive to end users, so the developers might like to consider looking into that. If you do get stuck, try the helpful FAQ section, or message an active user; when you sign up, someone is usually assigned to help you out, so you'll find a message from them in your messages - they'll be more than happy to guide you through anything you get stuck with!
Don't worry too much about the navigation niggles I've just mentioned - it's certainly interesting to see how gardeners around the world are blogging their various experiences; give it a visit some time, particularly if you want to read more about plants and gardens and take your plant-related blog to more readers (who doesn't!?).
You can find Orchids on a Balcony here on Blotanical.com.
I was actually told about blotanical by a user from the next site in the list...
Orchid Board, "Most complete orchid forum on the web"
User questions are answered quite quickly, and surprisingly you rarely get answers from existing users along the lines of "search function, learn how to use it" - instead, no matter how many times someone has asked Help!!!!1 My Phalaenopsis is Dying!!1!! someone will take the time to answer that query, perhaps with some reference to earlier threads, but never in a condescending manner or one that indicates the poster is an idiot who can't use a search function.
Of course, the forums have advanced users too, so you'll see plenty of topics that expand your knowledge of orchid culture and related subjects. Several orchid vendors and people with a vast knowledge of orchid culture regularly read the board and share their knowledge.
The board also has group growing "projects", where members vote on plants they would like to try their hand at growing, and where members share their growing experience with that species over time - a group learning exercise, or global e-learning evening class if you like! Another feature that might be of interest is the monthly photo contests, with both beginner and advanced categories.
One feature that brings me great joy is that users can immediately mark another user as a spambot when you notice one has invaded the system - this helps prevent the whole forum being over-run with rubbish and a huge clean-up job. You can also of course report posts to moderators, but the warning system puts an immediate posting ban on such users whilst the moderation team has a chance to review that user's behaviour.
If you're looking for an online community of orchid nuts (seed pods?) this is probably the one to join. There are of course others, but this does seem to be the most active and friendly of them. If you're looking for me, here's my profile.
Finally, we have folia, "Social garden tracker and organiser"
Folia can best be summed up as "facebook for gardeners"; if you're not blogging at the moment (and don't intend to start) this is probably the best place your can go to start your experiments in online social gardening - it's a pretty handy site even if you do have a blog. The site lets you keep journals of all your plants and how they're getting along, lets you build a wiki which adds to the knowledge of each and every plant on the site and of course share photos of your pride and joy.
Folia needs a number of users in your area before it really starts to come into it's own - for example, if you've got a lot of keen vegetable gardeners near you who are folia users, you'll find the site gives you regular suggestions of what you should be planting and harvesting at various times of the year.
An even more interesting feature is the "swap" functionality, where users are able to send each other spare seed/plant material they happen to have on hand. Just make sure you know what your local (and perhaps international) laws might be before you make use of it.
Should you get confused, there is an excellent help section - and if you get really stuck, the developers are friendly and helpful and pretty quick to respond considering the site is something they do in their spare time! Have a look at their tour (or just sign up and jump in). It certainly doesn't hurt that the whole site feels fresh and modern with a light, attractive colour scheme and sensible navigation. Web 2.0 hits the gardening world! You can find me here.
Now all they need to do is start pulling in blog feeds, and it'll be perfect...