When a young plant is ready to be moved into the garden, it is referred to as a seedling. This transition, known as transplanting, is stressful for the plant, and its success relies on careful preparation. The depth at which the seedling is placed is one of the most significant factors determining its immediate survival and long-term health. Planting at the correct depth ensures the root system can immediately begin anchoring the plant and absorbing water and nutrients efficiently. Incorrect depth, either by burying the stem too deeply or leaving the root system exposed, can lead to stunted growth or the eventual loss of the plant.
The Standard Rule: Planting at Soil Level
For the majority of flowers, herbs, and garden vegetables, the general practice is to transplant them at the exact same depth they were growing in their original container. This standard approach minimizes relocation shock by keeping the established junction between the stem and the roots exactly where it needs to be. The transplanting process should begin with digging a hole that is slightly wider than the seedling’s root ball but no deeper.
When removing the seedling from its pot, support the root ball to prevent crumbling and damage to the fine root hairs. Gently loosen any roots that may be tightly circling the soil mass, which is common in container-grown plants. Placing the seedling into the prepared hole involves ensuring the top surface of the root ball is level, or flush, with the surrounding garden soil.
Avoid mounding soil up around the stem or allowing the root ball to sit above the surrounding soil level. After positioning the plant, fill the hole with soil and lightly press it down to ensure good contact between the roots and the new soil. This eliminates air pockets that can dry out the roots. Finally, a thorough watering settles the soil around the root system, completing the process.
Understanding the Critical Stem Collar
The need to plant most seedlings at their original soil depth is rooted in the specific anatomy of the plant, specifically the area known as the stem collar. This collar is the natural transition point where the stem tissue meets the root tissue. Stem tissues are designed for above-ground functions, such as transporting water and photosynthates, while root tissues are adapted for subterranean absorption and anchorage.
Burying the stem above the collar in most plant species introduces a risk of stem rot and fungal disease. When the tender stem tissue is covered with wet soil, it struggles to breathe and lacks the natural defenses of root tissue. This makes it susceptible to pathogens like Pythium and Phytophthora. Conversely, planting too shallowly leaves the upper roots and the root collar exposed to the air and sun.
Exposure causes the delicate root structure to dry out quickly, leading to desiccation and reduced water uptake. Planting too high also compromises the physical stability of the seedling, leaving it vulnerable to wind damage and toppling. Maintaining the correct depth protects the integrity of the stem collar and supports the plant’s fundamental biological functions.
Key Exceptions: Seedlings That Benefit from Deeper Planting
A few notable plant families offer an exception to the standard rule of planting at the original soil line, primarily those that can produce adventitious roots. Adventitious roots grow from non-root tissue, such as a buried stem, rather than from the primary root structure. This unique capability is most famously exploited when transplanting tomatoes.
Tomato plants can be planted much deeper, sometimes burying up to two-thirds of the stem, to encourage a larger, more robust root system. The practice involves gently stripping off the lower leaves and then setting the plant into a deep hole or trench so that only the top few sets of leaves remain above the soil. The buried stem tissue will then generate new roots, dramatically increasing the plant’s ability to absorb moisture and nutrients.
Other plants that benefit from deeper placement include many members of the Nightshade family, such as peppers and eggplants. These should be buried only slightly deeper than their original depth, often just past the first set of true leaves. This technique is also used to correct “legginess,” which occurs when seedlings grow too tall and thin due to inadequate light. Leggy plants of many species, including broccoli and cabbage, can have part of their elongated stem buried to provide better stability and a stronger base, even if they do not produce adventitious roots as readily as tomatoes.