Royal star magnolia, Magnolia stellata, is a slow-growing deciduous tree that can reach heights of 15 feet (4.5 m) or more and can grow to be 15 feet (4.5 meters) wide. Royal star magnolia is native to Japan but has been naturalized throughout most of the world, including the United Kingdom, the United States, Europe and much of Asia. This species is unusual because it blooms in late winter through to early spring, before leaves have developed.
This species produces masses of star-shaped flowers that vary in color from bright white to pale pink. Flowers of the royal star magnolia are not tolerant of sharp frosts and, because it tends to flower during the winter and early spring months, this can pose a real problem in colder climates. Sharp frosts can cause discoloration of flowers, early flower drop and early flower death. If growing royal star magnolia in colder climates, it is advisable to plant it in an area that is protected from strong winds and extreme cold.
Royal star magnolia prefers partial shade and deep soil with high acidity. A grower wanting to increase soil acidity can liberally apply around the base of the tree farm yard manure from grazing animals such as horses, pigs, sheep and chickens. This will both increase the soil acidity and provide the tree — and any other plants in the vicinity — with extra nutrients.
The tree prefers well-drained soil. The royal star magnolia will not tolerate over-watering or periods of waterlogging. If water content in the soil is too high for prolonged periods, the royal star magnolia tree will quickly become unhealthy and more prone to disease and insect infestation, especially fungal diseases and root rot.
Although fairly disease resistant if grown in optimal growing conditions, the royal star magnolia is more likely to be the victim of disease if it has poor general health. The more common diseases occurring in royal star magnolia include fungal root rot, powdery mildew and magnolia leaf spot. If caught in the early stages, most of these diseases are easily treatable.
Leaf miners can infest a royal star magnolia and can cause large, unsightly holes in the leaves if a large infestation is present. Because royal star magnolia flowers in the winter and leaf miners are mainly active in the summer, the flowers are not usually affected. To minimize the risk of disease and insect infestation, it is advisable to remove dead leaves and any other organic matter lying beneath the tree, because fungi, diseases, insects and insect larvae can winter in garden mulch.