You might find these pictures interesting and relevant to this thread. The colander method used in Japan is primarily (and maybe exclusively) used for the development of substantial trunks on shohin bonsai in a fairly quick time. Yes you can get substantial trunks also in the ground but: a) those in japan who are most famous for this method do not have the land available; and b) you can better control the growth (both foliage and root) when the trees are pot grown.
Black pines are especially used for this because of their vibrant growth and because this is their home habitat! - but I observed other species used also with this method (though not as prevalent as black pine). One thing to keep in mind when you think that you might be able to duplicate the same speed of this method in your area is the climate difference. In the Shizuoka area, the climate is relatively mild year round and summers are hot (check the towel over the head of the person in picture #1 - it was 100 degrees F that day). They can get a LOT more growth in a shorter time than in a colder climate like New England, USA for instance.
I did visit Mr. Kusida Matsuo's nursery also but, because of his frail age, he has scaled back his work greatly. These photo's were taken at another small home nursery that Mr. Urushibata (my teacher) took us to where the owner (name forgotten) was most proficient at this method. The first picture is of Mr. Urshibata discussing some aspect of this technique with the owner. The black pines were in small colanders for two years and are then placed in larger grow pots or colanders for another 2-3 more years. After this approx. 5 year time of trunk development, the time is then spent developing branching, ramification, more budding, shorter needles, etc. This is the time where the trees are taken out of the double colanders, placed in bonsai pots or training pots. The second picture is a 3 year seedling (notice that it is planted in only a river stone). You can see that one leader is left to grow unrestrained - some were over 5 feet long. The third picture shows a trunk after 4 or 5 years (here you see that the first leader was cut and then a new leader was left unrestricted to create directional taper). The third picture shows a tree after about 10 years.
A couple of notes:
This grower planted his seedlings in ONLY crushed stone (or river sand)! They were watered multiple times a day and fed aggressively.
The main reason that the smaller colander is later placed in a larger one is mentioned by Graydon in post #16. Anytime we repot a tree there is a period of stress that slows the growth down. To minimize this, the tree is simply potted into a larger container so that the growth remains continuous - some roots escape to the larger colander to assure continued growth while there is some restriction for fine roots to develop in the smaller colander. There is obviously much more to this process than this and others have mentioned some of these other factors in above posts but that is the main rationale. The description in the pine book by Mr. Matsuo is a good one. Mr. Urshibata grows a lot of fabulous shohin gardenia at his nursery and had hundreds of colanders with shohin gardenia's developing in his 'back lot' area.
John Romano
Rhode Island, USA 'the shohin state'
if you are interested, you can read my shohin bonsai blog at:
http://knowledgeofbonsai.org/john_romano
