Q: Our southern magnolia hasn't bloomed for many years. It gets direct sun, and we've put alfalfa mulch around it for two years. When it bloomed last, in 1995, it was about 6 feet tall. Now it's about 14 feet tall, and is very full and green. The plant seems healthy, so where are the blossoms?

— Joe, Spanaway, WA

A: Roger Cook replies: Southern magnolia (Magnolia grandiflora) has creamy white, fragrant flowers that blossom in May, and it can grow to 80 feet high. It grows best in warm climates, Zones 7 to 9. The tree can survive in colder conditions, but the flower buds — the most tender part of the plant — often die during the winter. I don't think that's the cause of your problem, however. Spanaway is in Zone 8, the same as Charleston, South Carolina. More likely, the plant is missing some essential trace elements, or micronutrients. Call your local cooperative extension service to test the soil and help you determine the right balance. In my experience, nitrogen-rich soils encourage trees to produce more vegetative growth and fewer flowers, and the alfalfa mulch you're using is rich in nitrogen. I bet you need more phosphorus and micronutrients to stimulate root growth and flowering. To feed the roots, make holes around the drip line of the tree, 6 inches apart and 8 to 12 inches deep (a crowbar works great), and add super phosphate (0-20-0) and your recommended micronutrients according to the directions on the bags. If the tree still refuses to bloom, you can try planting the Grandiflora hybrids 'Edith Bogue' or 'Brachen Brown Beauty,' which are supposed to be the hardiest members of the species.
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