Hi Rob
I'd think the tree is struggling to cope with the new amounts of water it's getting. I have several swampies and they all crack to some degree. This is not a problem though. I actually place short vertical cuts into various parts of the trunks of my swampies and they thicken up and look weathered very quickly. It creates a craggy and rough texture to the tree and gives the appearance of age. Check out the April section in our website
http://www.toowoombabonsai.com and it shows a swampy getting airlayered and having the scored technique to add age to the tree. It's hard to imagine that the demo tree is only 8 yrs old. Incidentally, in our March webpage we have several photos of a great swamp cypress with terrific movement having several branches lowered with the inserted pebble method.
Also, you may like to consider airlayering your cypress, then you'd get two or three trees for your present one. Also, this would then give you two or three new trees with some good initial movement, rather than the tall straight tree you presently have. I have taken you photo and put some lines where an air layer could be placed, thereby giving you more trees. I have also numbered the branch that would be a possible new leader for the layer. You'll be amazed how simple it is (with a little bit of courage).
If you prefer to have a straight tree, then I'd be scoring and marking across the bottom of your tree now and then doing a trunk chop. This will get more taper into you tree. But if you are going to trunk chop, then why not air layer it and so you'll get you second tree for nothing.
Good luck with it all!
Stew
possible layering points with new leaders numbered.jpg
tree.jpg
tree2.jpg
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