Planting shrubs correctly is crucial for their long-term health and survival. While many gardeners focus on soil type or sunlight, planting depth is often overlooked, yet it is a common cause of plant failure. A shrub that is planted too deep or too shallow will struggle to establish a healthy root system, leading to a slow decline over several seasons. Learning how to properly prepare the plant and the planting site is fundamental to ensuring your new shrub thrives.
The Critical Rule for Planting Depth
The primary guideline for planting any shrub is to ensure it is placed no deeper than it grew in the nursery container or field. The goal is to set the top of the root ball level with the surrounding native soil, or slightly higher, particularly in clay or poorly drained areas. Planting just an inch or two too deep restricts the necessary exchange of water and oxygen to the fine root systems, leading to stunted growth and wilting. This lack of oxygen suffocates the roots, often mimicking the symptoms of root rot or drought.
Conversely, planting the shrub too high introduces problems for establishment. When the top of the root ball is significantly above the grade, it can dry out quickly, causing water stress and root death. High planting depth also reduces the stability of the shrub, making it prone to toppling before the roots can fully anchor into the surrounding soil. Aiming for a level or slightly elevated placement maximizes the plant’s ability to absorb water and nutrients while keeping the root crown properly aerated.
Identifying the Root Flare
Before digging, locate the root flare, which is the point where the trunk widens just above the roots. This junction must remain exposed to the air and should be at or slightly above the finished soil surface. The bark on the main trunk is not designed to be constantly buried and moist; covering it with soil can cause deterioration, cankers, and the development of unhealthy adventitious roots.
Nursery practices often result in the root flare being buried beneath excess soil or potting mix, especially in container-grown plants. To find the true root flare, use your fingers or a small trowel to gently scrape away the material from the top of the root ball until the widening of the trunk is clearly visible. This action is essential because the depth of the planting hole is determined by the distance from the bottom of the root ball to this newly exposed flare.
If planting a balled and burlapped (B&B) shrub, the root flare may be hidden by the burlap or accumulated soil. Pull back the burlap and remove the excess soil to ensure the flare is visible before placing the shrub in the hole. Failing to remove this material means the shrub will be planted too deep, regardless of the hole’s dimensions. Correcting the planting line on the shrub ensures the depth measurement is accurate for healthy long-term growth.
Preparing the Planting Hole
The planting hole should be engineered specifically to support the correct depth identified by the root flare. Rather than focusing on depth, the emphasis should be on making the hole significantly wider than the root ball, typically two to three times the diameter. The vast majority of a shrub’s feeder roots grow horizontally in the top 12 to 18 inches of soil, making a wide hole more beneficial for root establishment than a deep one.
The depth of the hole should be measured precisely from the bottom of the root ball to the exposed root flare, and the hole should be dug to match this height, or be slightly shallower. It is important not to loosen the soil at the very bottom of the hole, as this prevents the shrub from settling deeper into the ground over time. Placing the root ball on undisturbed soil provides a firm foundation, ensuring the shrub remains at the intended elevation.
Once the shrub is positioned in the hole with the root flare at the correct height, the native soil should be used as backfill around the sides of the root ball. Tamp the backfill gently to eliminate large air pockets, ensuring the shrub is held securely at the correct height relative to the surrounding grade. This careful backfilling process prevents the shrub from sinking and confirms the root flare remains visible and aerated at the soil surface.