Magnolia trees, celebrated for their early spring blooms and delicate fragrance, are often associated with warmer, southern climates. While classic, large-flowered varieties struggle in the upper Midwest, growing magnolias in Minnesota is possible with careful selection and site planning. Success depends on understanding the localized climate and choosing species bred specifically for cold tolerance to handle the region’s extreme cold and harsh winters.
Understanding Minnesota’s Hardiness Zones
The viability of any perennial plant in Minnesota is determined by the USDA Plant Hardiness Zone Map, which categorizes regions based on the average annual extreme minimum temperature. Minnesota’s climate primarily covers Zones 3, 4, and 5. Zone 3 experiences minimum temperatures between -30°F and -40°F, while Zone 4 ranges from -20°F to -30°F. The warmest areas, including parts of the Twin Cities metro, are designated as Zone 5a, where temperatures generally do not drop below -20°F. Magnolias rated only for Zone 5 or warmer, such as the Southern Magnolia (Magnolia grandiflora), will not survive a typical Minnesota winter. Selecting a variety rated for Zone 4 is the starting point for gardeners in the central and southern parts of the state, with Zone 3 areas requiring the hardiest available cultivars.
Cold-Hardy Magnolia Varieties
The secret to growing magnolias in a cold climate is choosing varieties that possess innate winter hardiness, typically rated to Zone 4. The Star Magnolia (Magnolia stellata) is one of the most reliable options, known for its exceptional cold tolerance and compact, shrub-like growth habit, generally reaching 10 to 20 feet tall. Its delicate, star-shaped flowers appear early in spring, and its hardiness allows it to tolerate the late cold snaps common in the region.
Another excellent choice is the ‘Little Girl’ series of hybrids, which includes popular cultivars like ‘Ann,’ ‘Betty,’ and ‘Jane.’ These were specifically bred to bloom two to four weeks later than other deciduous magnolias, significantly reducing the risk of flower buds being damaged by a late-spring frost. ‘Betty’ is often cited as one of the most cold-tolerant, sometimes surviving even in protected areas of Zone 3. These hybrids generally mature into small trees or large shrubs, staying between 10 and 15 feet tall.
Cultivars like ‘Merrill’ and ‘Leonard Messel’ are also successful Zone 4 options, resulting from crosses between Magnolia kobus and M. stellata. For those seeking maximum cold tolerance, the native Cucumbertree Magnolia (Magnolia acuminata) is the hardiest species. While its greenish-yellow flowers are less showy than other varieties, its ability to thrive in the coldest areas makes it a durable choice.
Strategic Site Selection and Planting Preparation
Successfully establishing a cold-hardy magnolia requires intentional site selection to create a favorable microclimate that shields the tree from the harshest elements. Planting the tree near the south or east side of a structure, such as a house or fence, provides a windbreak from prevailing northwesterly winter winds. This sheltered location also benefits from reflected heat and sunlight, which can slightly elevate the local temperature and protect spring buds from rapid temperature fluctuations.
Magnolias are shallow-rooted and require a deep, rich, and well-drained soil environment to prevent root rot and ensure proper nutrient uptake. The soil should be slightly acidic, with a pH between 5.5 and 6.5, which can be maintained by amending heavy clay soils with organic matter like compost or peat moss during planting. Poorly draining sites can be improved by planting the root ball slightly higher than the surrounding grade.
Spring is the ideal time for planting, allowing the tree the entire growing season to establish its extensive root system before the onset of the first winter. Once the tree is positioned, it is important to water it deeply and consistently during the initial establishment period to encourage robust root growth.
Essential Winterization and Year-Round Care
Even cold-tolerant magnolias benefit from protective measures to ensure survival through Minnesota’s severe winters. Before the ground freezes solid in late fall, the tree should receive a deep, thorough watering, as dry roots are more susceptible to freeze damage and winter desiccation. This hydration is an effective preventative measure against cold injury.
Applying a thick layer of organic mulch, such as wood chips or shredded leaves, around the base of the tree is necessary to insulate the shallow root system. This layer should extend out to the dripline but must be kept several inches away from the trunk to prevent moisture buildup and pest issues. For young trees, wrapping the trunk with burlap or a commercial tree wrap can prevent sunscald, a common winter injury caused by sun exposure on cold, clear days.
Routine care is straightforward once the tree is established. Pruning should be minimal and limited to immediately after the spring flowering period to avoid removing next year’s flower buds. It is important to situate the tree away from areas that receive road salt or de-icing chemicals, as the resulting high sodium levels can be toxic to the roots and foliage.