http://www.gardenexpress.com.au/forum/v ... php?t=4846
http://www.gardenexpress.com.au/forum/v ... php?t=4774
The first has two posts of trees in bonsai pots and the second has one. Take note of the different sizes and styles compared to the trees.
Shallow pots are much harder to maintain than deeper ones because they don't hold a lot of moisture and dry out very quickly. Very basically it comes down to Unglazed for pines, glazed for deciduous and flowering trees. Now, that is a very basic 'rule' because sometimes a deciduous or Broadleaf tree can look good in an unglazed pot. The pine family very seldom look their best in a glazed (and coloured) pot. The length and width of the pot is also a consideration. If the pot is a lot wider and longer than the tree is, it doesn't look natural - it looks totally out of balance. Likewise, if the tree has a thick trunk and a wide foliage spread on it, then it would look silly in a little pot barely larger than the trunk - it would always look as if it was about to topple over. The height of the tree, the foliage spread and the thickness of the trunk all play a part in selecting the 'right' pot for the tree. My advice until someone gains more experience at matching pots to trees is: If you think it looks good in a particular pot - then do it. One of my friends here has a Port Jackson fig growing in a glazed terracotta dogs water bowl (he drilled a couple of holes in the bottom) and it looks good. I'll go in to more technical detail in future posts on this thread - things like the spread of foliage, thickness of the trunk and height of the tree in relation to the dimensions of the pot, and also what specific pots to use for different styles of tree - with photos.
Here's a quick photo of the type of pot for a cascade and another for a semi cascade just to give you an idea.
Cascade. This one is in an Unglazed pot because I didn't have a glazed one at the time:

Semi Cascade. Although the second photo is a Chinese Elm on a rock (root over rock) it is also a Semi Cascade because of the branch on the right:
