How To Grow And Care For Bigleaf Magnolia

Magnolias are a dime a dozen in the South. Their leaves and flowers are familiar sights used in landscape design. A particular magnolia has been catching our eyes, and its massive, bright green leaves are a far cry from the waxy, deep green magnolia foliage that we're used to. While nearly every yard in the South hosts a species of magnolias, the bigleaf magnolia (Magnolia macrophylla) is less common in landscaping but still admiringly beautiful.

Bigleaf magnolia has enormous leaves. It has the largest simple leaf of all native North American plants. It also has the most significant single flower of the group. The oblong leaves can reach over two feet long and one foot wide. They're bright green on top and silvery beneath, and their size makes them perfect for casting shade and catching the wind. Magnolia macrophylla is a deciduous planting but can be semi-evergreen in certain areas.

Plant Attributes

Plant Attributes
Common Name:	Bigleaf Magnolia, Great-leaved Macrophylla, Large-leaved Cucumber Tree, Umbrella Tree
Botanical Name:	Magnolia macrophylla
Family:	Magnoliaceae
Plant Type:	Tree
Mature Size:	30-40 ft. tall, 20-25 ft. wide
Sun Exposure:	Full, Partial
Soil Type:	Loamy, Moist, Well-drained, Rich
Soil pH:	Neutral to Acidic (5.0 to 7.0)
Bloom Time:	Spring, Summer
Flower Color:	White
Hardiness Zones:	Zones 5-9 (USDA)
Native Area:	North America, Central America, Caribbean

Bigleaf Magnolia Care

The bigleaf magnolia is a large, deciduous tree with relatively low maintenance. It requires average water requirements and is moderately tolerant to droughts. Soil is one condition that needs monitoring, as it shouldn't be too wet or dry but also include organically rich nutrients. The silver-gray bark is thin, and enormous green and gray oblong leaves fit in more extensive landscaping settings as long as it avoids high winds. 

These large leaves only require regular pruning if your encounter diseased, damaged, or unsightly branches. The tree can grow to over 40 feet tall with a spread of 30 feet, typically reaching heights of 20 feet in favorable conditions. The bigleaf magnolia, blooming in late spring to early summer, features fragrant, creamy-white flowers that grow to 12 inches. The blooms take some time to appear—trees typically won't make them until they reach 12 to 15 years old. After the flowers appear, bigleaf magnolias also produce showy, three-inch-long red fruits shaped a bit like eggs. The fruits attract birds and require some clean-up, as do most magnolias.

Once established, magnolias take moderate water. They're picky with their moisture requirements and don't like waterlogged soil or long periods of drought. They thrive in rich, moist, well-draining soils requiring full or partial sun. In the right conditions, they grow about a foot per year.

Light

Full to partial sunlight is needed for bigleaf magnolias to grow. Trees should receive at least three to six hours of sun daily.

Soil

Bigleaf magnolias grow best in moist, organically rich soils that are well-draining and loamy. It does not tolerate soils that are too dry or wet. Similar to its native woodlands, the bigleaf magnolia grows best in areas with a slightly acidic to neutral soil pH.

Water

Balance is essential when watering bigleaf magnolias—too much or too little will prevent the tree from developing healthy foliage and blooms, leaving it susceptible to disease. Use your hands to feel the top inch of soil surrounding the tree to determine whether or not it is time for more water. The ground should remain moist and should use well-draining soil.

Temperature and Humidity

Bigleaf magnolias thrive in moderate to warm temperatures. Areas with extreme heat can encourage early flowering buds, damaging the potential for healthy blooms. Alternatively, places with colder temperatures will prevent trees from developing buds. Since bigleaf magnolias have large leaves, protecting these trees from harsh weather conditions such as high winds is critical. Adding a layer of mulch can help maintain an average-temperature environment surrounding the trees.

Fertilizer

Bigleaf magnolias only require a little fertilization if the soil is rich in organic nutrients. If trees are not experiencing new growth, slow-release nitrogen-rich fertilizer will help boost production. Apply fertilizer to the tree's base in the spring and a second application later in the growing season if the region experiences higher rainfall—or a lighter feed with potassium before dormancy.

Types of Bigleaf Magnolias

Bigleaf magnolias have cultivars that feature slightly differing characteristics. Here are some of the available varieties: 

• 'Purple Spotted': This tree features flowers with purple markings in the center. 
• 'Palmberg': A tree with huge flowers.
• 'Magnolia macrophylla var. ashei': Fragrant white flowers and large leaves grow on this tree, reaching about 10 to 15 feet. 

Pruning

Pruning is only required if diseased, damaged, or unsightly branches appear. Overall, little pruning is needed and can cause more harm than benefits. Providing trees with a superficial trim after finishing blooming during the spring or summer can help encourage new growth. If branches extend or cross over one another, consider trimming bigleaf magnolias to maintain a balanced formation.

Propagating Bigleaf Magnolias

Bigleaf magnolias can be propagated by collecting seeds from fallen fruit or rooting softwood cuttings in the summer. When collecting ripe, fallen fruit, remove and clean the seeds and store them in an airtight container in the refrigerator until it's time to sow them in the fall. Other than purchasing a bigleaf magnolia from a nursery, here is how to grow bigleaf magnolias by rooting softwood cuttings:

1. Start by taking cuttings about six to eight inches in the summer after the buds appear using a sterilized sharp knife or pruning shears. 
2. Place cuttings in clean water and remove the lower leaves. 
3. Make a two-inch vertical cut into the stem at one end and place it in a rooting hormone solution. 
4. Place cuttings in a small container filled with moist perlite. Keep the containers in indirect sunlight—adding a plastic bag around the container helps to keep in the humidity. 
5. Spray cuttings with water to keep the soil moist. Cuttings should sprout roots within a few months, and expect to see flowers about two years after planting if cuttings are successful.  
   

How to Grow Bigleaf Magnolias From Seed

Sowing seeds to grow bigleaf magnolias is possible, but purchasing a young tree from a nursery is easier. If you choose to grow trees from seeds, here is what you need to do: 

1. Purchase or collect seeds from pods in early fall when the fruit falls. 
2. Remove seeds from red fruit pods.
3. Soak the seeds in water overnight and remove any excess coatings the following day. Use a cloth to help remove the outer layers.
4. Place seeds in the refrigerator in an airtight container for up to three months. 
5. After removing the seeds, plant them in a moist sand or perlite container. Keep the container in indirect sunlight and continue to keep the soil moist. 
6. When the seedlings emerge, transplant the roots if overcrowded. 
7. Flowers can take up to 10 to 15 years to emerge, so continue care instructions for seedlings like a tree. 

Overwintering

Depending on your region's climate and preferences, leaving bigleaf magnolias exposed to colder temperatures to "chill" the tree or pruning to promote dormancy are options. In areas of freezing temperatures, protecting bigleaf magnolias is essential. Wrap blankets or tarp around the trunk and branches and add a layer of mulch to insulate shallow roots and the root ball.

Common Pests & Plant Diseases

While no significant pest or disease concerns exist, bigleaf magnolias are still susceptible to some issues. Leaf weevils are a type of beetle that eats leaves during the spring and summer, but these insects are easy to control by spraying the foliage with an insecticide.  

Yellow and brown spots can also affect bigleaf magnolias. Browning can result from a lack of water but can also indicate disease. If caught early enough, spraying a copper-based fungicide will help stop the infection before it attacks the leaves. Yellowing leaves indicate a nutrient deficiency in the soil, so a simple soil test can determine what is needed.

Since bigleaf magnolias feature enormous foliage, protecting them from high winds is one of the best ways to preserve these trees. 

How to Get Bigleaf Magnolias to Bloom

Deadheading is not necessary for bigleaf magnolias. Getting the tree to bloom can be a long process, so maintaining proper care with consistent watering, full sun, and nutrient-rich soil is the best way to get these trees to bloom. Removing spent blooms can help encourage new growth, but it also is a way to improve the symmetry and shape of the tree.

Common Problems With Bigleaf Magnolias

Leaves Turning Yellow

Oversaturating the soil is one reason that bigleaf magnolias' leaves turn yellow. After yellowing, the foliage will wilt and drop off. Mushy stems from overwatering can cause the tree to look dull and unhealthy. In addition to adjusting the watering schedule, ensuring the soil has the right balance of nitrogen and iron with a soil test can help determine the reason behind yellowing leaves. If the soil's nutrients are unbalanced, adding fertilizer can help get bigleaf magnolias back to healthy.