Nursery stock, root flares, and planting depth

Nursery Stock Types and Seasonal Planting Windows in the PNW

Landscape contractors work with three distinct categories of nursery stock, each requiring specialized handling, storage, and installation schedules:

Comparison of Stock Types and Windows

1. Bare-Root (BR) Stock: Field-grown deciduous trees and shrubs harvested while dormant with all soil washed or shaken from the roots. Extremely cost-effective and lightweight, but exceptionally vulnerable to desiccation. Roots must be kept continuously moist (packed in damp shingle tow, sawdust, or hydrogel) and protected from freezing temperatures. The planting window in Western Oregon is strictly confined to the dormant season (late November through March) before bud swell.
2. Ball and Burlap (B&B) Stock: Field-grown trees dug mechanically or by hand with a cohesive ball of native field soil, wrapped in burlap, and bound with sisal or synthetic twine within an open steel wire basket. Preserves approximately 10% to 20% of the tree's original root system. Best planted from late autumn through early spring (October through April) while the canopy is dormant or semi-dormant. B&B stock is extremely heavy and must always be lifted by the root ball or wire basket—never by the trunk.
3. Containerized Stock: Plants grown entirely within plastic containers (#1, #5, #15, #25, or larger) in artificial, high-porosity potting media (composted fir bark, peat moss, pumice, or perlite). Retains 100% of the roots formed within the pot. Although container stock can technically be planted year-round if supplemental irrigation is provided, the optimal planting window in the Pacific Northwest is autumn (October through November). Warm autumn soils (50°F to 60°F) and seasonal rains allow roots to establish throughout the mild winter before summer drought arrives.

Excavation Geometry and Root Flare Identification

The physical dimensions and geometry of the planting hole dictate how rapidly roots expand into native surrounding soils:

Dimensional Standards

• Hole Width: Must be excavated 2 to 3 times the diameter of the root ball or container. More than 90% of a tree's absorbing feeder roots occupy the top 12 to 18 inches of soil and grow outward horizontally. Loosening soil in a wide radius eliminates physical boundary resistance, allowing young lateral roots to penetrate quickly into native ground.
• Hole Depth: The depth of the hole must strictly equal the distance from the bottom of the root ball to the root flare, or 1 to 2 inches shallower. The bottom of the pit must remain firm, undisturbed native soil. If the hole is excavated too deep and backfilled with loose soil, the weight of the tree and water settling will cause the plant to sink over time.
• Sides of the Hole: Excavation sides should be sloped outward (saucer-shaped) rather than vertical. In heavy clay soils, smooth pit walls glazed by backhoe or auger buckets must be scarified with a hand spade or pick to break the smooth boundary layer and allow root egress.

Locating the Root Flare (Trunk Flare)

The root flare (or trunk flare) is the distinct basal transition zone where the trunk widens and the first primary structural lateral roots branch outward into the soil. In modern container and B&B nursery production, soil or potting media is frequently mounded around the stem during mechanical cultivation or up-potting, burying the true root flare 2 to 6 inches below the surface.

Root Ball Preparation and Remediation

Nursery production methods inevitably generate root system defects that must be mechanically corrected prior to backfilling:

Containerized Stock Remediation

When container-grown roots reach the smooth plastic container wall, they deflect horizontally and circle the perimeter, forming a dense, tangled cage. Left untreated, circling roots will never grow outward into native soil.

• Root Shaving: Using a sharp hand saw, spade, or heavy pruning knife, shave off the outer 1/2 to 1 inch of the root ball's entire perimeter and bottom. This removes the outer layer of circling roots, exposing healthy radial root tips.
• Box Cutting (Slicing): For smaller stock (#1 to #5 containers), make 4 to 6 vertical slices approximately 1 inch deep from the top to the bottom of the root ball, and slice an "X" across the base. Tease out the sliced root ends radially outward.