Magnolias are known for their flowers, but planning where to plant one requires focusing on its ultimate size. Because the magnolia family includes everything from small shrubs to towering evergreen giants, the required space depends entirely on the species. Considering the tree’s mature dimensions is necessary to avoid significant maintenance issues and property damage later on.
Magnolia Species and Expected Mature Size
Determining planting space requires identifying the specific magnolia type, as mature size varies widely across the genus. Large, evergreen species like the Southern Magnolia (Magnolia grandiflora) reach heights of 60 to 80 feet. They typically develop a mature canopy spread of 30 to 50 feet, requiring substantial open space to accommodate their dense, pyramidal form.
The medium-sized deciduous Saucer Magnolia (Magnolia × soulangeana) is a common landscape choice. This hybrid matures to a height and spread between 20 and 30 feet. This size makes it a suitable specimen tree for many suburban yards, but it still needs a generous planting area to display its rounded crown.
For smaller gardens, the Star Magnolia (Magnolia stellata) offers a compact solution. This species is often grown as a multi-stemmed shrub or small tree, reaching 10 to 20 feet in height. Its spread is modest, ranging from 10 to 15 feet at maturity, allowing placement closer to structures or in tighter garden beds. Always consult the expected mature size of the specific cultivar, as some varieties are bred to be more compact than the species standard.
Determining Necessary Canopy Clearance
The required planting area is defined by the canopy radius, which is half the total mature spread. The tree trunk must be positioned so the mature canopy edge will not interfere with surrounding objects or other plant life. For instance, a Southern Magnolia with a 40-foot spread needs a minimum radius of 20 feet of clearance in all directions.
Adequate clearance ensures proper air circulation throughout the foliage. Lack of airflow, often caused by crowding against a wall or another tree, can trap humidity and lead to fungal diseases. Even light distribution is important for the tree’s shape; magnolias planted too close to a building will grow lopsidedly as they stretch for sunlight.
Planting multiple magnolias or placing one near other large trees requires careful planning to prevent canopy and root competition. Trees should be spaced so their mature canopies are slightly separated or just barely touching, allowing each one to develop its natural form. Crowding limits resources available to each tree and can result in stunted growth or a weakened structure.
Mandatory Setbacks and Root System Considerations
Magnolias have thick, fleshy root systems that are broad and shallow, often extending horizontally near the soil surface. Unlike many trees, the majority of roots grow only in the top 18 to 24 inches of soil, sometimes spreading two to four times the canopy width. This growth habit means the roots are prone to interfering with surface-level hardscapes and underground utilities.
The expansive, surface-level root structure can easily heave and crack concrete sidewalks, driveways, or paving stones over time. To mitigate this damage, the tree trunk should be planted a minimum distance from any paving surface or foundation. A practical rule of thumb is to plant the trunk no closer to a permanent structure than 1.5 times the expected mature canopy radius.
Additionally, the shallow roots are attracted to the moisture and nutrients found within sewer and water lines. Roots will exploit even the smallest crack or loose joint in older pipes, leading to blockages and potential plumbing damage. For most magnolia species, it is recommended to maintain a distance of at least 10 to 20 feet from any underground utility line to minimize the risk of root intrusion.