It will depend on what type of magnolia it is. There is the southern magnolia (Magnolia grandiflora) which is an evergreen tree and deciduous types such as star and saucer magnolias (Magnolia stella and M. soulangeana respectively) that are commonly used in the landscape.

Propagation methods for each type are provided below.

Southern Magnolia

Leafy cuttings of M. grandiflora, taken from late spring to late summer, wounded, and treated with IBA at 5000 to 20,000 ppm have rooted well with bottom heat (75 degrees) and intermittent mist. Semihardwood cuttings root well when five-second quick-dipped in 5000 to 10,000 ppm NAA in 50 percent alcohol. To obtain survival of the rooted cuttings through the following winter, they should be rooted early enough in the season so that some resumption of growth will occur before fall.

Star and Saucer Magnolias

M. stellata and M. soulangeana are successfully propagated by leafy softwood cuttings. These may be taken from late spring to late summer after terminal growth has stopped and the wood has become partly matured. 

Excellent rooting can be obtained if cuttings are taken from very young plants, the bases wounded, treated with auxin, then rooted in sand or coarse perlite in outdoor mist beds. Under such conditions, rooting is rapid and in high percentages, and there is little trouble from diseases.

(Source: Plant Propagation Principles and Practices, Hartmann, Kester, and Davies, 5th Edition)

For more information on propagating landscape plants see our publication - E-917 Propagation of Ornamental Plants for Oklahoma.