The answer is nuanced: it is possible to reduce a magnolia’s size, but this process goes against the tree’s natural growth patterns and requires a specific, thoughtful approach. Magnolias generally thrive with minimal pruning, so any attempt to keep them small is a long-term commitment that must be done correctly to maintain the tree’s health and characteristic shape. Incorrect pruning can stress the tree, leading to an undesirable appearance and potential health problems. Success depends on understanding the tree’s biology and applying techniques that encourage controlled growth rather than aggressive reaction.
Understanding the Natural Growth of Magnolia Trees
Magnolia trees possess a growth habit that makes them naturally resistant to being kept small through heavy pruning. Most species, such as the Southern magnolia (Magnolia grandiflora), mature into large, imposing specimens with a dense, pyramidal crown, while deciduous varieties like the saucer magnolia (Magnolia × soulangeana) spread broadly. This inherent tendency toward size and shape means they do not readily accept significant height or width reduction.
The tree’s response to aggressive cutting is a defense mechanism that often defeats the pruner’s purpose. Heavy pruning triggers the growth of numerous, fast-growing, vertical shoots known as water sprouts or epicormic shoots. These shoots are weakly attached, grow straight up through the canopy, and create a dense, unnatural, and often unattractive appearance.
Removing these water sprouts only encourages the tree to produce more of them, creating a cycle of intensive, constant pruning. The ideal is to select a variety that is naturally smaller, like the ‘Little Gem’ cultivar of M. grandiflora or the ‘Little Girl’ series of deciduous magnolias, which reach a more manageable mature height of 12 to 20 feet. For larger species, the goal of pruning should be size limitation over several years, not drastic size reduction in a single season.
Strategies for Restrictive Pruning
Size control in a magnolia relies on selective removal to maintain a natural, open canopy, which is distinct from simple maintenance pruning. The most effective technique is selective thinning, where an entire branch is removed back to its point of origin, such as the main trunk or a larger lateral branch. This method reduces the overall volume of the canopy while preserving the tree’s characteristic form and allowing for better air and light circulation.
Another technique for reducing the length of a branch is a reduction cut, which shortens a limb by cutting it back to a healthy, smaller side branch. For this cut to be effective and minimize regrowth, the remaining lateral branch should be at least one-third the diameter of the branch being removed. This directs the tree’s growth energy into the smaller side branch, slowing the overall extension of the canopy.
Never “top” a magnolia, which involves cutting large main branches back to stubs. Topping creates severe wounds and guarantees a profusion of weak, vertical water sprouts, leading to a disfigured tree that is prone to disease and decay. Likewise, shearing the magnolia to a hedge-like shape should be avoided, as this also creates dense, unnatural growth and sacrifices the tree’s distinctive large flowers.
Timing and Minimizing Pruning Damage
The timing of pruning is a primary consideration for magnolia health and future flowering. Deciduous magnolias, which typically bloom on old wood, should be pruned immediately after they finish flowering, generally between mid-summer and early autumn. Pruning at this time prevents the accidental removal of the next season’s flower buds.
Pruning deciduous varieties in late winter or early spring must be avoided because magnolias are known to “bleed” sap heavily from the cuts, which can stress the tree and attract pests. For evergreen varieties like Magnolia grandiflora, pruning is best done in late winter or early spring, just before new growth begins.
To minimize damage, use only sharp, clean pruning tools to ensure a smooth cut that facilitates rapid wound closure. Cuts should be made just outside the branch collar—the slightly swollen area where the branch meets the trunk—to allow the tree’s natural defense mechanisms to seal the wound effectively. Removing too much wood at once also stresses the tree, so any significant size reduction should be spread out over several years, removing no more than 10 to 15% of the live canopy annually.