Sweetbays want to be a lovely, graceful tree, single stemmed or multiple. Trying to keep it to a bush will, I think, produce something not worth growing. No blooms anyhow.

We had a sweet bay that volunteered in our yard in Wilmington NC. Within a a couple of years it was about 5 feet and producing flowers, When we left after 8 years it was 8 to 9 feet tall. As I said this was a volunteer so the cultivar was what ever naturally occur on that part of the Carolina coast. We loved the fragrance. Wished it produce a heavier canopy of leaves. It is not a big tree and will always be an understory tree. We had one that was on the lot when the house was built and was about 20 feet tall. One of the puzzles was its lack of leaves. One year we learned why. There was one old female squirrel who apparently like the smell of sweet bay leaves in her nest. Each time she had a litter, she would take as many leaves as she thought necessary to make her nest. This left the sweet bay nearly stripped of leaves near the end of the summer. This happened each year for the 8 years we lived in the house.

In California USDA 9 you could try some of the many kinds of evergreen Asian magnolias that were imported for some years by Piroche Plants, Pitt Meadows, BC and distributed to retail outlets in North America. These provided combinations not available from the North American species such as pink flowers with bluish leaves, yellow flowers with bluish leaves, early spring flowers - all on evergreen trees, most of them with smaller, more slender leaves as with sweetbay magnolia (although southern magnolia is highly variable with anything from small, narrow, pointed leaves to platter-like blunt ones being produced by different individuals). Unfortunately, Piroche Plants was apparently terminated by Sudden Oak Death so a continued supply from them is no longer assured. The kinds of magnolias they were providing are ones they listed under the old generic names Manglietia, Michelia and Parakmeria. Genetic analysis has shown these to be as Magnolia as magnolias can be, but you will often find them listed by outlets under these other genera. See the web site of the Magnolia Society for photos of the flowers of various kinds, as well as a discussion of putting the other genera into Magnolia. For a document listing and describing 8 kinds for mail-order sales (use the binoculars and search with the term "magnolia")... Here is a link that might be useful: CistusMailOrderCatalogFall2008.pdf

Bumping up this good question since there has not been a reply.