I have a deciduous magnolia. It makes violet-pink flowers. This summer it has started to turn yellow and lose its leaves. Do you know if it depends on excessive or insufficient irrigation, or on some fungus / parasite?
Thanks in advance
soulangeana magnolias are hybrid shrubs, whose ancestors have Asian origins; it is a shrub or small resistant tree, which generally does not suffer excessively due to pests or diseases; unlike many other species of magnolia, it tolerates alkaline or neutral soils well, as well as summer heat or winter cold. But even these shrubs have an Achilles thallus: generally they do not like to be watered much, or in any case a heavy and always damp ground; for this reason, after the plants have stabilized in a garden, in the ground, there is a tendency to let them be satisfied with the rain water. Clearly, every year the seasons are very different from the previous ones, with periods of a particular climate; for example, spring 2013 was very wet and cold, and this climate may have favored the development of root rot, or in any case may have weakened the plant. As they suffer from the excesses of water in the soil, soulangeana magnolias can suffer the same way due to lack of watering, which becomes particularly heavy if the climate is dry, and free of rain, for long weeks, in summer. Since you do not indicate what care you lavish on your magnolia, it is difficult to lean towards one problem or another. These shrubs use much of their energy to produce large spring flowers; this often causes a state of poor vigor in the shrub, which in the following months tends to lose part of the foliage prematurely, either because of water problems or because of problems linked to nutritional deficiencies. Usually it is a sporadic event, which does not involve the loss of much of the vegetation, and later, when autumn arrives, the shrub loses all its foliage, and enters vegetative rest, which allows it to recover from the summer vegetative stress, to prepare for the following year's flowering. So, if the leaves that fall are just a few, quite sporadically, don't worry, it's normal, and could depend on the annual climate trend. If instead the leaves that fall are so many, check the humidity of the soil, if it is excessive septums to water; if instead the soil is dry and dry, try to water it abundantly, at least once a week before the arrival of autumn. Before the vegetative rest, sprinkle on the ground a little mature manure or slow release granular fertilizer.