Magnolia trees and shrubs provide some of the most beautiful large flowers for gardens, blooming anytime from late winter to midsummer, depending on species and climate. Their flowers appear singly on branch tips and range in shape from saucer-, cup-, goblet- or starlike. Magnolias aren't particularly long-lasting when a flower display arises, ranging anywhere from one to four weeks. Environmental conditions play a significant role in the duration of a flowering season.
Worldwide, about 80 species of magnolias exist, plus even more cultivars of the most ornate species. From a horticultural standpoint, magnolias are discussed as being spring or summer blooming. Spring-flowering types most often are deciduous trees, while evergreen magnolias tend to bloom when temperatures are warmer, in late spring and summer. Among the most well-known deciduous, spring-flowering magnolias are the saucer magnolia (Magnolia x soulangeana), star magnolia (M. stellata) and lily magnolia (M. liliflora). The most famous evergreen, late spring- to summer-blooming magnolia is the southern magnolia (M. grandiflora). Deciduous summer blooming magnolia trees include cucumber tree (M. acuminata), swamp magnolia or sweetbay (M. virginiana) and the umbrella tree (M. macrophylla).
Flowering Season Duration
In some years, a magnolia tree or shrub may be in bloom for only one week, while other years as long as five or six weeks. Spring-flowering magnolias most often display open flowers for one to two weeks. However, since their colorful and swelling flower buds appear on naked branches, the flowering season seems to last longer, perhaps two to three weeks. Summer-blooming magnolias also create a more concentrated period of flowers across their leafy canopies over the course of two to three weeks. Since temperatures are warm, sporadic flowers may appear later into the summer or early fall.
The Role of Weather
For spring-blooming magnolias, temperatures play the dominant factor in timing and duration of flowers. Once flower buds swell and reveal petals, frosts and subfreezing temperatures will kill blossoms. An untimely frost or freeze can prevent or cut short the magnolia flowering season. Moreover, cool temperatures -- from 40 to 65 degrees Fahrenheit -- cause spring magnolia flowers to swell and open slowly over as long as three to five weeks. Warmer temperatures cause flowers to quickly open and wither. Summer-blooming magnolias bloom when it's warm, but hot temperatures cause individual blossoms to open faster and brown more quickly. Any magnolia tree stressed by drought may not sustain flowers as long or in as great of number compared to a healthy plant growing in an evenly moist, cool soil.
Temperatures vary by geographic location and also contribute to the timing of magnolia flowering as well as the duration of the flowering season. In the Deep South, spring-flowering magnolias such as the star magnolia bloom as early as late February and into mid-March. At higher elevations in the South, blooming begins two to four weeks later. In the North, the star magnolia doesn't bloom until April. The onset of warmth in spring and summer affects when blooming occurs, and the weather patterns that year determine how long the flowers last on the magnolia's branches.