Michelia alba is an evergreen tropical tree from Southeast Asia beloved for its wonderfully fragrant flowers. In its native habitat, this tree can get to 30′ high and wide and is often used as a street tree. It is believed to be a hybrid between Michelia champaca (another fragrant tree in its own right and the source of the word ‘Shampoo’) and Michelia montana, a Malaysian species. Possibly due to its hybrid origin, Michelia alba rarely set seeds in the garden, so most propagation is done by grafting or air-layering. This difficulty in propagation makes Michelia alba usually twice as expensive as Michelia champaca, which can be easily propagated from seed and is often used as rootstock for Michelia alba. One master hobbist friend of mine, Calvin, has successfully propagated Michelia alba in all possible ways, including softwood cuttings and occasional seeds.
In the Bay Area, Michelia alba is not completely hardy outside. Young trees will be killed to the ground and mature ones get heavily damaged during once-every-ten-year freeze events. However, if you have a corner with nice micro-climates such as a south-facing courtyard, you can successfully grow Michelia alba in ground. I have seen mature trees in Oakland and San Francisco. For most people, however, container is the best solution. During bad freezes, one can just move the treasured plants into a more protected place, such as under eaves for moderate freezes, and into garage for severe freezes. One issue with containerized Michelia alba is that its root system will use up all the nutrient and soil space after a few years. Repotting into slightly bigger containers will work for several years, but eventually the gardener has to either plant it in ground or do a surgery called root pruning. According to Calvin, one has to time this pruning just before a new flush of leaves is coming out (usually there are three flushes of new leaves every year), take the tree out of its pot and skin off an one-inch-thick layer of roots for a quarter of the whole exposed root surface. Let the plant recuperate in half shade for a couple of weeks afterwards and maybe thin out a few top branches to balance the water needs. I have not done it myself but will probably have to try it in a few years.
Since Michelia alba has very fleshy roots, well drained soil with lots of perlite and compost is ideal. One feeding recipe I got from a former commercial Michelia alba grower, Charles Lee, is to mix 5 tablespoons of fish emulsion and 1 tablespoon of water soluble 20-20-20 fertilizer such as Miracle Grow together with 5 gallons of water. Use several cups of this solution everytime Michelia alba is watered during the growing season (May to October). It is also important to remember to skip it and flush with lots of plain water once every month to avoid salt build-up. The results are lush, glossy foliage with loads of big, plump flowers throughout the growing season. The reason for this magical formula is that fish emulsion not only supplies all kinds of beneficial compounds, but also significantly lowers(acidifies) the pH of our tap water (pH = 9.0 in Mountain View) to about ph=4.0. The 20-20-20 fertilizer is just like bread and dessert rolled into one. Try it and you will be amazed how this diet would push a Michelia alba into pumping out waves after waves of flowers.