The choosing of the correct pot for the plant can be complicated. There are a myriad of pots available, from basic, factory made pots to pots that can be made to order. The are, however, some basic things to keep in mind that can make the decision easier.
First it must be determined what size pot should be used. Once again, the species being potted will have some determination on the depth of pot to be used. Generally speaking, the thicker the trunk, the deeper the pot should be. From an aesthetic point of view, long pots should have a length of about two-thirds the height of the tree. For a round pot, the diameter should be about a third of the tree height. Style should also be considered. For Cascade or Semi-cascade, a deep pot should be used to balance the look of the bonsai. A rectangular pot with straight edges is appropriate for the Formal Style, and the Informal style works with most types of pots.
Many bonsai enthusiasts classify plants into masculine and feminine categories. Deciding which category a plant is can make choosing a pot easier, for some pot shapes will compliment the masculine, and some the feminine.
A masculine tree may have a strong trunk and dense canopy. It will give a general image of strength, with angled branches and rough bark. A deep, square or rectangular pot that also has angled lines would be suitable for a masculine tree. The characteristics of the feminine tree include smoother bark and more flowing branches, with light foliage towards the top. Feminine-type pots will be shallower and round, with rounded edges. Of course, many trees will have both masculine and feminine characteristics. The idea is to determine the primary features, and match them to a masculine or feminine pot. Ultimately the bonsai enthusiast will have to do what they feel is right.
Finally, the color and texture of the pot should be taken into account. The color can be chosen to compliment some aspect of the tree, for example the bark or foliage. Not surprisingly, heavily textured pot with go well with a masculine plant, and a smooth pot compliments a feminine one. Ultimately, though, bonsai is an art form, and many different styles may be considered, including contrasting ones. The end effect should be of a unified, striking image.