Plum trees are members of the Prunus genus, which includes cherries and peaches, and are valued for their sweet, colorful fruit. The mature size of a plum tree varies widely based on the selected variety and how it is grown. Understanding these dimensions is important for successful garden planning, as planting a tree that outgrows its space can lead to maintenance issues and poor fruiting. Plum trees range from towering standard varieties to small, manageable dwarfs.
Defining the Maximum Dimensions
Plum trees are sold in three general size classifications, each corresponding to a distinct range of mature height and canopy spread. Standard, or full-sized, plum trees can reach heights between 15 and 30 feet, often developing an equally broad canopy. These vigorous trees require significant space and typically take longer to begin producing fruit. Semi-dwarf varieties mature to approximately 12 to 15 feet tall, offering a more manageable size for the home orchard. Dwarf trees are the smallest options, remaining compact at about 8 to 10 feet tall and wide. This size allows nearly all maintenance and harvesting to be done without a ladder.
The Controlling Factors of Tree Size
The final size of a plum tree is primarily controlled by the rootstock, the root system onto which the desired plum variety is grafted. Nursery growers use specific rootstocks to intentionally restrict the tree’s natural vigor, a process known as dwarfing. For example, ‘Pixy’ creates true dwarf trees, while ‘St Julien A’ is commonly used for the medium-sized, semi-dwarf structure.
The rootstock controls size by regulating the uptake of water and nutrients from the soil, limiting the tree’s overall growth potential. This limitation allows the tree to divert energy into fruit production earlier in its life, a trait known as precociousness. Standard trees are often grown on highly vigorous rootstocks, such as Prunus cerasifera seedlings, allowing them to reach their full height.
Cultivar selection also influences the tree’s overall shape and size, independent of the rootstock. European plums (Prunus domestica) tend to be more upright and vase-shaped, reaching the taller end of the size spectrum. Japanese plums (Prunus salicina) are often slightly smaller, maturing to around 10 to 12 feet with a more spreading growth habit. Environmental conditions, such as poor soil or insufficient sunlight, act as secondary modifiers and can result in a tree that is smaller than its genetic potential.
Practical Methods for Size Management
Beyond the genetic control provided by the rootstock, pruning remains the most effective tool for managing a plum tree’s size after planting. Because plum trees are prone to the fungal disease Silver Leaf, pruning must be performed during the summer months when the tree is actively growing and can quickly heal its wounds. Pruning during the dormant winter season is discouraged, as open wounds are susceptible to infection from fungal spores.
Summer pruning, typically done from mid-June to August, is used to reduce the tree’s overall size and vigor. Removing branches and leaves during the growing season takes away the tree’s photosynthetic capacity, effectively slowing its growth. Conversely, winter pruning stimulates vigorous new growth in the spring, as the tree attempts to rebalance its large root system with a reduced canopy.
For extreme space constraints, training methods like fan training allow a plum tree to be kept to a two-dimensional form against a wall or fence. This method, which requires a minimum area of about six by six feet, relies on constant, precise pruning to maintain the flat shape. Growers often train plum trees into an open center or goblet shape. This involves removing inward-growing branches to maximize light and air penetration, which helps limit height and encourage fruit production.