My Japanese Magnolia tree has bloomed prolifically for years. But last year and this year, the blossoms are fewer and less robust looking. Could less watering because of Ca drought regulations be killing the tree?
Japanese Magnolia Tree
Here is an article on magnolia blooming problems. Get a soil test from Cal Extension Service. https://www.gardeningknowhow.com/ornamental/trees/magnolia/magnolia-blooming-problems.htm. It drought by itself caused the problem, I believe you would have seen leaf curl and leaf drop last summer during bud formation. If yours is simply not making buds in fall, nutrient deficiency may be to blame or you may be growing it outside the recommended zones 5-9. Look up your AHS Heat Zone. This magnolia is rated for 9-5 but the ag and AHS zones are different. http://www.plantmaps.com/interactive-california-heat-zones-map.php