The weeping cherry tree (Prunus subhirtella ‘Pendula’ and similar cultivars) is a highly valued ornamental tree, admired for its cascading branches and abundant spring blossoms. Homeowners often select this tree for its aesthetic appeal in residential landscapes. However, a common concern involves its underground structure: how its root system develops and what implications that growth has for nearby structures. This article details the characteristics of the weeping cherry’s roots, their growth patterns, and steps for managing their proximity to built environments.
Understanding the Weeping Cherry Root System Anatomy
The root system supporting the weeping cherry’s graceful canopy is not native to the weeping variety itself, but belongs to a different, more vigorous cherry species. Almost all commercially available weeping cherry trees are created through grafting, where the weeping branch tissue (scion) is joined onto a robust rootstock. This rootstock, typically a standard upright cherry variety, is chosen for its hardiness, disease resistance, and ability to thrive in various soil conditions.
The rootstock dictates the tree’s underground behavior, resulting in a system that is shallow and wide-spreading, similar to many other ornamental trees in the Prunus genus. Unlike trees that develop a deep, anchoring taproot, cherry trees grow a fibrous network close to the surface. This network includes fine feeder roots tasked with absorbing water and nutrients.
Quantifying Root Growth: Depth and Lateral Reach
The majority of the weeping cherry’s root mass remains close to the surface to access oxygen, which is less available deeper underground. Generally, the most active root growth, comprising 80 to 90 percent of the system, occurs within the top 12 to 18 inches of soil. While some roots may occasionally penetrate deeper, the overall habit is to spread laterally rather than vertically.
The horizontal spread of the root system can be extensive, reaching far beyond the tree’s canopy, or drip line, as the roots seek out moisture and nutrients. A common arborist guideline suggests that the roots may spread out two to three times the width of the tree’s canopy. For instance, a mature weeping cherry with a 20-foot wide canopy could easily have roots spreading 40 feet or more away from the trunk.
The specific depth and spread of the roots are significantly influenced by the surrounding soil type. In dense, compacted, or clay-heavy soils, the roots tend to stay shallower and spread wider to compensate for poor drainage and low oxygen levels. Conversely, in loose, well-drained sandy soil, the roots may penetrate a bit deeper, though the wide-spreading nature remains constant.
Assessing and Preventing Structural Damage
The shallow, wide-spreading nature of the weeping cherry’s roots presents specific challenges for nearby hardscaping elements. As the roots thicken over time, they can exert upward pressure, leading to the cracking and lifting of sidewalks, driveways, and patios. This is particularly noticeable when pavement is installed directly over the primary root zone. Roots may also pose a risk to utility lines or septic drain fields, as they are drawn toward the consistent moisture found within these systems.
Damage to solid foundations is generally rare and often misunderstood, as tree roots do not typically penetrate solid concrete. Instead, issues can arise if a tree is planted too close to a structure, allowing roots to pull significant moisture from the soil directly beneath the foundation. This moisture loss can cause the soil to shrink or settle, which may destabilize an already weakened or shallow foundation.
Preventing future damage requires strategic planning before the tree is planted. For hardscaping like sidewalks and driveways, maintaining a separation of at least 8 to 10 feet from the trunk is a highly recommended measure. When planting near a house or building foundation, a distance of 10 to 20 feet is advisable to minimize any potential risk.
In high-risk areas, such as near a septic field, the tree should be planted a minimum of 25 feet away to accommodate the full lateral reach of the mature root system. For situations where a tree must be placed closer to a structure, a subterranean root barrier can be installed to physically redirect roots downward and away from the vulnerable area.