Plum trees, members of the Prunus genus, are popular fruit-bearing deciduous trees whose mature size varies significantly. A plum tree’s final height is determined primarily by the root system it is grown upon and the cultivation methods used, not the species alone. Understanding these factors is important for selecting a tree that fits the intended space. This guide outlines specific expectations for plum tree size and the techniques growers use to manage height effectively.
Understanding the Mature Height Classifications
The most significant factor determining a plum tree’s ultimate size is the rootstock onto which the desired plum variety is grafted. Growers classify these combinations into three primary size categories, each with a predictable height range. Standard plum trees represent the most vigorous growth, typically reaching a mature height of 18 to over 30 feet, depending on the species and environment. These trees develop deep, expansive root systems, making them suitable for large orchards or properties where maximum yield is the goal.
The semi-dwarf tree offers a balance between manageable size and good fruit production. Often grafted onto rootstocks like St. Julien A, these trees mature at a height between 12 and 18 feet. This reduced size simplifies harvesting and maintenance without requiring specialized equipment. Semi-dwarf trees are a common choice for home gardeners, offering a more compact canopy that still produces a substantial crop.
Dwarf plum trees are the smallest option, ideal for limited spaces, containers, or intensive planting systems. Frequently grown on rootstocks such as Pixy or Krymsk 1 (VVA-1), they generally reach a mature height of 6 to 10 feet. The low height simplifies care, including spraying and pruning, and the fruit size remains consistent with larger trees. Some dwarf rootstocks require permanent staking due to a less robust root system.
Genetic and Environmental Factors That Determine Growth
Genetic vigor, primarily conferred by the rootstock, sets the upper limit of a plum tree’s height potential. The rootstock controls the scion’s growth by regulating the uptake of water and nutrients, effectively dwarfing the tree. For example, a cultivar grafted onto a standard rootstock will attain its full height, but the same cultivar on a semi-dwarf rootstock will have its vegetative growth limited by the restricted root system.
The species of plum also contributes to the intrinsic growth habit and height. European plums (Prunus domestica) tend to be naturally less vigorous than many Japanese plums (Prunus salicina), often reaching a mature height between 10 and 20 feet. Japanese plums frequently exhibit more vigorous, upright growth. This difference may necessitate more active management to maintain a desired size, so the choice of species should align with the grower’s intent for size control.
Beyond genetics, the environment dictates whether a tree reaches its full size potential. Plum trees thrive in deep, well-drained loamy soils with a slightly acidic pH, ideally between 6.0 and 6.8. If the soil is compacted, waterlogged, or has a pH below 5.8, root development becomes stunted, hindering the tree’s ability to absorb necessary nutrients and water.
Climate is another factor that affects growth and height. Plum trees require a specific number of chill hours (time spent between 32°F and 45°F) during winter dormancy. Failure to meet this requirement leads to delayed and uneven foliage development, inhibiting the robust vegetative growth necessary to achieve the expected mature size. Optimal soil and climate conditions allow the tree to maximize the height determined by its rootstock.
Practical Methods for Controlling Plum Tree Size
Growers can actively limit a plum tree’s height and spread through specific pruning and training techniques. Summer pruning is effective for size control because it has a devitalizing effect, slowing the overall growth rate. This contrasts with winter pruning, which encourages a flush of new growth in the spring. Summer pruning, ideally performed after harvest, diverts the tree’s energy away from excessive height gain.
Two common pruning cuts are used to shape and limit vertical growth. Heading cuts remove the end portion of a branch, encouraging the development of lower lateral branches, making the tree bushier and shorter.
Thinning cuts remove entire branches back to the main trunk or a larger limb. This opens the canopy for better light penetration and air circulation while reducing the overall volume of the tree.
Specialized training systems are also employed to physically restrict the tree’s dimensions. Espalier and fan training involve tying branches to a flat structure, such as a wall or trellis, limiting the tree to a two-dimensional plane. This method prevents the tree from achieving a tall, rounded form. Additionally, growing a plum in a container restricts the root system, acting as a form of natural dwarfing that keeps the tree significantly smaller than its in-ground potential.