ALL bonsai should be in fast draining gritty soil, it's the proportion of organics (bark, coarse loam, etc.) that changes, and it's very hard to say which trees will do best with what percentage (beyond very basic info) because you don't know where they live, in or out, heating, what sun they get, etc. It's more important to learn each tree's needs in it's particular environment by observation than to try and use a quick fix.

Around the fringe of a swamp: (this is for my area but you can look up which will work for you) Coast Redwoods Sequoias Western Red Cedars of many varieties (but they don't like standing water for long) Shore Pine (Pinus contorta var contorta) Leylands Blue Atlas Cedars Gingkos Red Horsechestnuts Purple Robed Locust (Robinia 'Purple Robe') Giant Dogwood (Cornus controversa) Quaking Aspen Catalpa Sugar Maple Raywood Ash Green Ash Nellie R Stevens Hollies Himalayan White Birch Japanese Maples Quercus virginiana Quercus myrsinifolia In the swamp: (6-11" pooling water in winter) WILLOWS -- Prairie Cascade Willow -- awesome, truly amazing tree Babylonica Weeping Willow Curly Willows Blue Arctic Willows Rosemary Willows Nishiki Dappled Willows Red Barked Willow (Salix alba 'Chermesina') Violet Willow (Salix daphnoides) Lapland Willow (Salix lapponum) Bay Laurel Willow (Salix pentandra) Swamp Tupelo (Nyssa aquatica) American Sycamore Buttonwood (Platanus acerifolia 'Bloodgood') London Plane Tree (Platanus occidentalis) Sweetgum Black Cottonwood Bald Cypress Blueberries 2 kinds of swamp Eucalyptus Swamp White Oak Swamp Red Maple Swamp Magnolia River Birch Alder

The black gumbo clay is super fertile and I know you don't want to use it, but if you put in a layer of the compost/sandy loam and a layer of the clay, you should have something that drains a bit better and is easier to work in. The bigger issue is that when you dig out the clay and fill in with better (read more friable) soil, you get a bowl effect and the water still doesn't drain. Personally, I prefer to raise the level with a good compost/sandy loam mix because it drains better. I just build beds on top of the clay, raising the level as high as I can because the beds will eventually settle some. Just my opinion, I'm sure others have great ideas too. Pam

g'day daleblack, better late than never maybe hey? but here goes. first questions (as i have never used brunning gypsum), was the gypsum of a moist talcum powder type consistancy? second if yor soil is like it sounds why fight it? use raised beds for all gardens, if you wanted to you could do a raised bed first where the trees are going then plant the trees in to rasied bed, the main thing with trees is their feeder roots need to be well drained the tap root will pretty much find its own way. so for trees that need good feeder root drainage you need to plant them into a raised position that is you dig a slight hole into your original soil throw some good quality gypsum in (usually the best stuff is bought at a produce agency) then create a mound to what ever height you need over and above that to plant the trees into (might be anywher up to 1/2 the heith of the current root ball?), this is necessary with citrus in those heavy soils so you may get some clues from researching planting citrus trees. len Here is a link that might be useful: len's garden page