and third: has anyone tried to make a mangrove bonsai? i have wondered that for some time, maybe plant it in a tall glass tray with a couple inches of salt water over the soil? (the glass being to highlight the roots and water)
I assume you mean Florida red mangrove - Rhizophora mangle. I've been growing one in a container for years and I can tell you there are so many misconceptions about this plant floating around the internet masquerading as facts. Firstly, although red mangrove has some truly amazing adaptations which allow it to live with its feet in salt water, they do not require this. They do not need salt in the air either. They do not need salt and/or intertidal conditions to throw prop roots. The reason they are only seen in the wild in salty and brackish water is more about their very slow growth being non-competitive in other environments rather than about their supposed need for that environment. A word of caution is that once sprouted they can not move freely between salinities, so it is important to either choose an unsprouted propagule, or you'll have to get the information about what salinity it was sprouted in, and slowly adjust it to the salinity where it will be growing. If growing in salt water, the leaves will become coated in excess salt if they are not regularly cleaned off with freshwater. If growing in freshwater you'll want to rinse them just to keep dust off but they won't need it every day.
All that said, they are really not a very good choice for bonsai. I have seen many references claiming that they are used but have yet to see even a picture of a finished red mangrove bonsai. They grow sllloooooooooowly. Painfully slowly. Slower than any other plant I have ever grown. Internodes are long, leaves are large. They tend to grow a fairly tall skinny trunk before they branch. Mine is about seven years old and is now about three feet tall, with three naturally formed branches, all in the top third of the canopy. If you try to trunk chop it, it will probably die. If you defoliate it, it will probably die. They are notoriously sensitive to pruning, especially if the leader is cut back before natural branching occurs. I have never pruned mine, above or below, and it is just getting to the point where I am considering some careful pruning in the spring. If I can get it to backbud it might someday be considered a very large size bonsai, and definitely an aquired taste aesthetically. I haven't tried it yet but it seems like the branches could be wired. I can't remember if these are copper sensitive (buttonwoods are) but I would stick with aluminum wire just in case.
They need bright light. They love sun. In the summer they want it hot and humid, and they start to pout in the winter if temperatures drop below about 45º. The secret to aerial roots in a container is of course high humidity, but also instability. When the canopy above becomes so dense that the trunk starts to keel over, the tree responds by pushing a prop root out to hold itself up. It's really that simple, no salt or intertidal conditions required. They are also surprisingly tolerant of drought conditions at the appropriate time of year, I keep mine pretty wet in summer but drier in the winter.
I grew mine for years in a container with no drainage as recommended by lots of mangrove sites out there until this winter I started to really think about that and decided it could not be the optimum way. In particular I was very sparing with the fertilizer because there was no way to flush the pot. And I thought this was more like a swamp than anything resembling an intertidal situation. The container it was in was a big patio pot with no drainage holes, it narrowed towards the top a bit. After it popped its first aerial root I pictured it with a few more and realized I had to get it out of that pot now while it was still possible. I had never liked the pot it was in, it was just one I had handy. So I decided to switch it over to a different setup. I researched a lot and decided that the best course of action was to plant it in the sort of mix I see recommended for buttonwoods (2/3 of a good bonsai mix - I used Turface, pumice, and a bit of coconut husk chips plus charcoal, mixed with 1/3 crushed shell). I moved it to a large open bowl shaped container, unglazed, with drainage. I use a large glazed saucer below as a water reservoir. It handled the repotting pretty well, but I took pains to disturb it as little as possible and didn't cut any roots since I was potting up to a roomier container instead of trying to put it back in the old one. I rinsed as much of the old mix out as I could, but I didn't try to break up the rootball at all. I don't think it is really out of the woods yet, we'll see how it does in the spring. There was probably a pretty big shift in pH that I should have considered as part of my planning but it is too late now.
