Although I am not in your region, here on the Island we have very poor soil as well, either all rock or clay. Nevertheless, I have had success with ammending my soil. The ammendments you are considering would all help your clay a great deal.

I am assuming that you have a variety of tropicals. If that is the case, your plants have different soil needs. For the plants you have that like it on the dry side, you will want to have a good percentage of sand and small gravel added to your soil. As far as the sand from your creek, if you can be certain that there are no chemical polutants in it then it should be great as there is usually alot of decomposing plant matter, etc, in creeks. But it is risky without knowing exactly what is in the "ditch".

The peat, compost, and manure(well composted) will be beneficial to the quality of your soil for most of your tropicals. You likely cannot put enough of this into your soil, particularily for the BIG growers that like their moisture such as colocasias, bananas, cannas, etc. Most of us underestimate how much "good soil" our gardens need. My advice would be to double the amount you are thinking of!

I have only used perlite or vermiculite in my potted plants. It is very helpful in the pot. If you have enough organic matter added to your garden soil I don't think you would need it.

As far as an "organic" fertilizer goes, other than manure, I have had great success with adding alfalfa pellets (rabbit food) to my soil. It is very inexpensive-$7 for a large 50 lb bag. For a new bed, dig it in or for an existing one I have to bury it under the top few inches as I do have wild rabbits here! Everything in my garden, palms, bananas, perennials, etc, love the nitrogen and grow like mad. The leaves on my palms stay nice and dark green. Bloodmeal also helps to keep the leaves green on my palms. I add a handfull at planting.

I wish you luck and in general, I have found, the amendment process is neverending. Each year I continue to add more to my soil.

P.S. Don't forget to take before and after pictures!

I live in High Point. My bananas, cannas, and alocasias grew well last year in my clay, although I did work a little compost into the holes when I planted them. This weekend I got 2 tons of compost from the city facility ($40) which I used to fill two new raised beds and I'm going to till it into my heavy clay planting areas. I'll probably throw some cow manure in there, too. I'm not organic, though; I used a lot of Peters and Miracle Grow last year.

Basically tropicals like more soil amendments than less since they continually feed and have no dormant period.

I think I killed the crown of my windmill-it rotted as I had it in too much shade/water. I poured peroxide into the crown and moved it to a sunnier/drier spot (yes, I have heard of copper fungicide, but prefer organic gardening). The bigger leaves are staying on and still look green and healthy. Hopefully it comes back. I think I learned pretty quick that my main tropical garden has too much shade for palms-oh well, I guess I'll have a nice indoor garden for the winter again for my ponytail, sago, chinese fan. Obviously if I rotted the windmill these guys won't overwinter outside. I am proud to say that I now have added to the tropical garden:
bamboo,
cleopatra cannas
split leaf philo.-selluom
oleander
purple potato bush
red-hot poker
giant dahlias
four o' clocks
more hostas (whirlwind, gold standard, janet, some gold/geen lakeside)
caladium
asiatic lilies
calla
purple oxalis
wandering jew
trailing verbena
I don't exactly have a plan, but I am leaving most plants in their pots around for now to shuffle them around and decide, etc. If anyone has a brugmansia to trade, I would be thrilled-email or post me.

--------------------------------------------------------------------------------