The bigleaf magnolia (Magnolia macrophylla) can be a stunning addition to the landscape. The oblong to obovate leaves on this magnolia tree can measure up to 3 feet long and 1 foot wide, hence the species name of macrophylla, which is Latin for "large leaves." The leaves are medium green on top and a silvery color on their undersides. The tree bears fragrant white flowers that are equally impressive and massive, with a span of roughly 8 to 12 inches. Even the elongated red fruits that follow the flowers offer visual interest. The fruits also are popular with birds and other wildlife.
The tree has a moderate growth rate, gaining around a foot per year and forming a pyramidal shape. It can be planted in the fall or early spring.
|Botanical Name||Magnolia macrophylla|
|Common Names||Bigleaf magnolia, large-leaved cucumber tree, great-leaved macrophylla, umbrella tree|
|Mature Size||30–40 ft. tall and wide|
|Sun Exposure||Full, partial|
|Soil Type||Loamy, moist, well-drained|
|Soil pH||Acidic, neutral|
|Bloom Time||Late spring to early summer|
|Flower Color||Creamy white with purple petal bases|
|Hardiness Zones||5–8 (USDA)|
|Native Area||Caribbean, North America, Central America|
Bigleaf Magnolia Care
Bigleaf magnolias are easy to care for when grown in optimal conditions. They do not suffer from any serious pest or disease issues, nor do they require regular pruning to maintain their shape. If you do need to prune to remove a misshapen branch, try to do so in the late winter or early spring. This will prevent the sap from bleeding. Remove any dead, damaged, or diseased branches as they arise.
A drawback of bigleaf magnolias is it can take a decade or longer for them to begin to produce blooms. Also, because the leaves are so large, raking them can be quite a chore in the fall. Furthermore, they are fairly fussy about the soil in which they grow. They do not like very dry or very wet ground. And they are intolerant of pollution, meaning they do not make good street trees.
Bigleaf magnolia trees need a site that has full sun to part shade. Two to five hours of direct sunlight each day is typically sufficient.
These trees prefer conditions that mimic their native woodland habitat. Loamy soil that is high in organic matter and drains well is ideal. And a slightly acidic to neutral soil pH is best.
Bigleaf magnolias don't do well in soggy or bone dry soil. Always allow the soil to dry out somewhat between waterings, but never allow it to stay dry for too long. Water when the top inch of soil is dry to the touch. Bigleaf magnolias grown in exceptionally well-draining soil will need more frequent watering than trees grown in slow-draining soil types.
Temperature and Humidity
The bigleaf magnolia tolerates the temperature highs and lows of its growing zones well. Humidity also typically is not an issue as long as the tree's moisture requirements are met. A layer of mulch around the tree can help to keep the roots cool and retain soil moisture. One specific climate requirement of bigleaf magnolia trees is a location that does not experience strong winds. Because the leaves of this tree are so large, they are easily damaged by wind gusts.
When grown in organically rich soil, bigleaf magnolias often don't need supplemental fertilizer. Signs that fertilizer is necessary include weak new growth in the spring and significant dieback. Use a slow-release fertilizer with a balanced formulation, and apply it during late spring or early summer
Bigleaf Magnolia Varieties
The bigleaf magnolia has been divided into three subspecies that some people treat as separate species. They are:
- Magnolia macrophylla subsp. macrophylla: Known also as bigleaf magnolia, this tree sports leaves that can stretch from 20 to 36 inches long. And the tree itself can grow more than 60 feet tall.
- Magnolia macrophylla subsp. ashei (also Magnolia ashei): Known as the Ashe magnolia, this tree can grow up to 40 feet high. And its leaves stretch around 10 to 24 inches long.
- Magnolia macrophylla subsp. dealbata (also Magnolia dealbata): This tree has two common names: the Mexican bigleaf magnolia and the cloud forest magnolia. It can grow more than 60 feet high with leaves around 1 to 2 feet long. Its fruits also are fairly large at around 3 to 6 inches long.
Propagating Bigleaf Magnolia
Most growers prefer buying bigleaf magnolia trees from nurseries, but the trees can also be grown from seed. Collect ripe, fallen fruit from the ground, and remove the flesh, leaving only the seeds. Clean seeds can be stored in an airtight container in the refrigerator. Sow the seeds in the fall, but be aware that bigleaf magnolia seeds are known for having low seed viability. If you're not keen on trying your luck with the seeds, bigleaf magnolias can also be propagated via rooting softwood cuttings in the summer.