My Sweetbay Magnolia Is Losing Leaves

Soil pH

• Across its native range of the southeastern United States, sweetbay magnolia grows mainly in moist, acidic soils. The acidity ensures that certain nutrients are more available for absorption by the roots. Neutral to alkaline soils cause a nutrient deficiency, causing leaf yellowing and often the abortion of leaves. Leaves drop to conserve moisture and nutrients for the greater plant. It is less serious to drop ephemeral tissues such as leaves compared to extensive dieback of twigs and roots.

Moisture

• Simply put, sweetbay magnolia trees excel in moist soils. If growing conditions become too dry, leaves display a yellow color instead of the usual light green, or leaf edges dry and become brown. Sandy soils drain water quickly, and if organic matter is absent, these conditions create an overly dry soil that can cause premature leaf drop. Newly planted sweetbay magnolias need to be deeply irrigated for six months to ensure that the root ball doesn't dry out and the root system grows well and establishes itself.

Humidity Insight

• Even if the garden soil is fertile, acidic and moist, some leaves may drop off the sweetbay magnolia if ambient humidity is low. In this case, even more soil water is needed to offset the loss of water from the leaves to the arid air. Hot, dry winds cause the same problem. If you live in a windy area or the climate normally provides hot winds or inconsistent rain in the summer, plan on irrigating more, and plant the magnolia in a wind-protected location in the garden.

Pests and Diseases

• Sweetbay magnolias growing in ideal garden conditions rarely succumb to fungal diseases, which can cause a disruption to vascular tissues and cause leaf drop. Likewise, if the plant is healthy, insect pests don't inflict serious damage. It's when the magnolia is stressed from drought or lack of nutrients that insect infestations result in more profound damage. Sucking insects cause leaf drop as they dehydrate the leaf tissues. Look on leaf undersides for signs of thrips, scale, mealybug or spider mites.