Q: We have a mature Galaxy magnolia tree. It was here when we bought our house in 1993, but it was quite small. It is located on the west side of our house in a small area between our master bedroom and a tall covered patio, so it has probably received significantly less sun over the years than I suspect it needs. It has now reached only about 12 feet in height and 8 to 10 feet in diameter, but has grown each year and seemed to be relatively healthy. Each spring (around May), the tree blooms first, then the leaves appear and grow fully and rapidly. I believe that’s normal for this variety of magnolia. However, shortly after the tree’s leaves are fully developed and the tree looks extremely healthy (within about two to three weeks), the leaves rapidly start to turn brown and fall off. By late June, only about a third of the green leaves are left and there are still some more leaves that are yellowing and turning brown. Is this normal? It seems to happen every year. Or is there a problem that we need to address? Does the tree need a fertilizer or perhaps more acidity?
G. K. Greeson, Gold River
A: According to UC master gardener Barbara Mantzouranis, the Galaxy hybrid magnolia was introduced in 1980 by the National Arboretum, and is considered unique among cultivated magnolias. This deciduous tree displays pyramidal upright growth, with a narrow crown, and is very suitable for small landscapes and areas with limited space. Having a moderate growth rate, it can reach 30 to 40 feet tall with a 22- to 25-foot spread at maturity.
Magnolias require sun and rich well-drained soil to thrive, but will tolerate heavy clay soil if drainage is adequate. Regular summer watering is needed to produce optimum flowering and healthy growth of this tree, but well-established trees can get by with occasional watering during dry weather. Magnolias tend to be sensitive to activity in or around the root area, so foot traffic and gardening under these trees should be minimal.
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As is typical with this variety of magnolia, bright purple flowers appear before leaves in spring, so your tree seems to be doing well in that respect. But no, it is not normal for the tree to begin losing leaves within three weeks after they develop, and there is clearly something amiss.
There are leaf diseases, vascular diseases and cultural practices that can cause this malady in your tree. Unfortunately, your inquiry raises many questions that must be answered before an accurate diagnosis of the problem can be reached.
Occasional dead leaves sporadically spaced throughout the canopy are of no concern. However, it sounds as if your tree actually defoliates by roughly two-thirds by early summer. Repeated, prolonged defoliation takes a toll on trees. At more than 20 years of age, yet only 12 feet tall, your tree is quite dwarfed. Given the very small stature of your tree, it may not be receiving enough sunlight for optimal growth.
It is not recommended that you take any remedial measures with the tree until such time as you have pinpointed the problem. Fertilizing an ailing tree is not recommended unless a nutrient deficiency has been established.
When a tree is under stress and losing leaves, it is a very bad idea to fertilize, since the tree has to create enzymes that convert the fertilizer into a usable form for uptake, and this is an energy intensive task for the tree. This activity takes energy that the tree needs to use in rebuilding parts that it is losing, which in this case is leaves. And if the cause of the ailment is not a nutrient problem, the tree has expended a great deal of energy to convert this material which it will not use, at a time when energy should be focused on survival.
It is recommended that you take samples of both damaged as well as healthy leaves into the master gardener office that serves your county for help in visual identification of the problem. Since we are near the end of this growing season, leaves may not be available, so visual inspection may have to wait until leaf flush in the spring. Pictures of the tree and the growing site will also be helpful. The master gardeners also can talk to you about cultural practices.
The Sacramento County Master Gardener office is at 4145 Branch Center Road, Sacramento. Give them a call at (916) 876-5338 for walk-in office hours.
Questions are answered by master gardeners at the UC Cooperative Extension services in Sacramento and Placer counties. Send questions to Garden Detective, P.O. Box 15779, Sacramento, CA 95852. Send email to firstname.lastname@example.org. Please put “Garden Detective” in the subject field and include your postal address. To contact UC Extension directly, call:
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