I have wanted to try growing pines in plastic colanders for a while and finally got around to it. In the book ‘Pines’ published by Stone Lantern there is an article titled ‘Pine from seed’ written by Kusida Matsuo that explains how he grows pine seedlings in plastic colanders using 7 parts sand and 3 parts akadama with no organic material. This provides excellent aeration of the roots and promotes vigorous growth. The only downside to this technique is that you must water the trees several times a day to keep the roots from drying out and fertilize heavily because the potting mix and colander drain very quickly. Skipping a day of watering could prove fatal to the tree.
I am going to use 100% crushed lava as my potting mix. Our bonsai club buys about 100 bags a year from Roy Nagatoshi in California. The shipping is steep but the quality of his material is the best I have found. As you can see the lava pieces are fairly small. It drains well but still maintains some moisture in all those tiny pockets.
Matsuo’s technique placed one small 6 inch colander inside another larger 8 inch colander. I placed my colander inside a plastic deck rail pot filled with more crushed lava. The reason I chose to do this is for convenience. I wanted to have the pots on my deck so I could easily water the trees as I rushed out to work each morning. A second reason is the exposed colander would dry out quickly with a little wind and the deck rail pot should solve most of this problem. If my potting mix appears to be drying out as summer gets hot I will probably apply a thin layer of leaf mulch to slow evaporation.
Matsuo claims that the trunk should be about 2 inches in diameter after one year. I hope to match his results.