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Planting Shrubs Correctly

When to Plant

In South Carolina, fall is the best season to plant shrubs for optimal root growth and successful plant establishment. From the fall through the winter, the above-ground structures of most ornamental plants go dormant and cease growth. However, plant roots continue to grow since the soil does not freeze. These conditions allow shrubs planted in the fall to use the carbohydrates produced during the previous growing season for root growth. When spring and summer arrive, the root growth that has occurred since the fall can better access the necessary water and nutrients for optimum plant growth.

During the establishment period, it is essential to provide adequate and appropriate moisture. However, shrubs planted during the spring through summer require more careful monitoring of soil moisture during the hot and dry season when there is a higher risk of drought. Newly planted shrubs have fewer roots available to meet the water needs of actively growing shoots during the spring and summer.

Preparing the Soil

Soil Testing & Soil pH: Before starting any planting project, test the soil to determine soil pH and nutrient availability. When fertilizer or a soil pH-adjusting amendment (such as lime) is necessary, the soil test results will provide instructions for how much to add.

Perform a soil test several weeks before planting; three to four months before planting is ideal because it takes 8 to 12 weeks for lime to affect soil pH change.

Many of the plants grown in South Carolina prefer slightly acidic soil. Fortunately, many South Carolina soils are naturally acidic. Depending on the soil’s acidity, lime may be needed to raise the soil pH into the ideal range. Occasionally, soil pH may be too high for plants such as azaleas and blueberries. In this instance, lower soil pH using aluminum sulfate or sulfur. See HGIC 1650, Changing the pH of Your Soil for more information.

NOTE: It is essential to follow the soil test results. Attempting to adjust soil pH without a soil test can result in nutrition problems that are difficult to correct. Soil testing is available for a nominal fee through the local county Extension office. For further information on soil testing, refer to the fact sheet HGIC 1652, Soil Testing.

Organic Soil Amendments: Organic matter improves nutrient and water-holding capacity and the overall physical characteristics of the soil. However, some gardeners add too much organic matter, resulting in unbalanced soil chemistry and poor soil structure that detrimentally affects plant growth.

Plant tags will often recommend adding organic matter when planting individual shrubs. However, research suggests it is better to backfill the planting hole with only the native soil. Amending the backfill causes the soil structure of the planting hole to differ dramatically from the surrounding native soil. This dramatic difference in soil structure encourages the plant roots to stay within the planting hole rather than moving out into the native soil.

In heavy clay soils, the sides of the planting hole can become glazed similar to the inside of a terra cotta pot. Use a shovel or mattock (similar to a pickaxe) to notch out the sides of the planting hole to help newly growing roots more easily move into the surrounding soil.

Hand dug planting hole with notched walls to enhance root spread into the surrounding clay soil.

A hand-dug planting hole with notched walls will enhance root spread into the surrounding clay soil.
Joey Williamson, ©2012 HGIC, Clemson Extension

When preparing a planting bed for more than one shrub, incorporate organic soil amendments throughout the entire planting area to create a uniform growing environment for the roots. Add no more than 10 to 20 percent organic matter by total soil volume. For example, when preparing a bed to 8 inches in depth, only add 1 to 2 inches of organic matter to the bed surface, then till well. For heavily compacted clay soils, it may be necessary to relieve compaction by subsoiling or deep tilling before adding organic matter. For more information about adding organic materials to the soil, see HGIC 1655, Soil Conditioning – Establishing a Successful Gardening Foundation.

Shrub Bed Preparation

Start by selecting the right plant for the space. For more information, see HGIC 1050, Site Considerations When Selecting Plants. If the area is deemed suitable but has poor drainage, elevate the bed 8 to 12 inches using native soil or topsoil purchased from a reputable supplier.

Unfortunately, there is no industry standard for topsoil. The definition of topsoil is simply the soil layer at the top of the soil profile. Look for topsoil made up of mostly native soil and a relatively small portion of composted organic matter. Organic matter found in topsoil should be small particles in which the organic source material is unrecognizable.

Additionally, plant shrubs high to allow the water to drain away from their roots, allowing access to much-needed oxygen. In extreme cases, it may be necessary to install a subsurface tile (black, corrugated pipe) drainage system to help carry water off the site.

When shaping the final grade of the planting bed, rake the area smooth to eliminate low spots where water is likely to collect. To help achieve proper drainage, shape beds to carry excess moisture away from buildings to areas where it can slowly percolate into the soil. While few ornamental plants tolerate long periods of standing water, plants used for rain gardening do well with occasional flooding. For more information about rain gardening, see the Carolina Rain Garden Initiative.

Remove any debris left on new construction sites where creating planting beds. Concrete, roofing shingles, tar, oil spills, paint, and sheetrock can cause long-term plant growth problems. Soil compaction can also be a problem on construction sites due to heavy equipment use and constant foot traffic. Deeply till the soil and incorporate organic matter to relieve compaction.

Inspecting & Preparing the Root Ball

Shrubs are usually sold in containers, balled-in-burlap, or bare-root.

Container Plants: Nurseries start shrubs grown in containers as seeds or cuttings in soilless media (potting soil). Containers are usually plastic but can be made from wood or biodegradable products. Before planting containerized plants, inspect the root ball for root defects that may have occurred during propagation or while in inventory at a nursery.

Shrubs grown in plastic containers are progressively ‘potted-up’ to a larger pot as they mature. During potting-up, sometimes, the topmost roots of the shrub are buried too deeply in the container. It is crucial to conduct a thorough inspection of the root ball to find the root flare and topmost roots of the shrub. The root flare occurs where the trunk gradually widens as it approaches the soil line. This area is where the trunk transitions into the topmost roots just below the soil surface. Dig the planting media away from the top of the root ball to locate the root flare and uppermost roots before planting.

Often, adventitious roots will grow along the trunk of a shrub that has been planted too deeply in its container. These roots are not the topmost roots. Remove them down to where the root flare transitions into the uppermost roots.

Contrary to popular belief, most plant roots prefer to grow uniformly around the trunk, extending outward radially rather than deep down into the ground. So, when plants are not potted-up at the correct time during production, the roots grow to the side of the container where they begin to grow horizontally along the inside of the plant pot or vertically in search of free soil space. If this growth occurs for too long, the roots begin to grow over each other, causing the root ball to produce circling roots and become root-bound. Research suggests once plant roots start growing in a circling pattern, they do not readily correct their growth outward when removed from the container and planted in the ground. Therefore, roots circling in the pot are defective.

Always examine the root ball of container-grown plants for defects and correct them before placing them into the ground. Circling roots left on the shrub at planting can later grow into a girdling root around the trunk of the shrub. Girdling roots eventually cause plant failure by strangling the water and food conducting structures of the plant.

At a minimum, identify and remove circling roots using a machete, serrated knife, or spade shovel. Shear off the outer 1 to 2 inches of the root ball of pot-bound shrubs. For reference, think of it as making the round root ball into a square with the cuts. After the initial shearing, gently tease out the roots growing along the outside of the root ball. Using a sharp hand pruner, cut them back to where they begin to circle. New root growth will occur at these cuts. This new root growth will grow radially from the trunk of the shrub.

An alternative method for many container-grown shrubs is root washing. When root washing, wash the potting mix away from the roots to examine the root ball more closely. Prune circling, kinked, or otherwise defective roots using a sharp pair of hand pruners. Place the shrub in the planting hole and arrange the roots radially from the trunk of the plant. Though this sounds like an extreme practice that could kill the plant, plants are resilient and often have a better establishment and survival rates using this technique. When planting root-washed plants, it is imperative to plant in the fall to reduce plant stress while they become established. Additionally, careful attention to the water needs of the plant is essential.

Balled-in-Burlap (B-n-B): Balled-in-Burlap, also called “B-n-B” or “field-dug,” are field-grown plants dug by hand or machinery from the field. The root ball is wrapped in burlap, then placed in a basket or tied with straps or twine to secure the burlap. Nails may also be used to secure the burlap.

B-n-B shrubs are root-pruned in the field to prepare the plants to be dug at the appropriate time. Root-pruning allows the shrub to harden-off properly to reduce the stress of digging. Unlike container shrubs, B-n-B plants usually do not have problems with circling roots. However, the root flare of B-n-B shrubs is often buried when plants are dug and burlapped.

When planting B-n-B shrubs, untie the burlap from the trunk of the shrub and remove soil to find the root flare and topmost roots before digging the planting hole. The root flare and uppermost roots of the shrub should be at or slightly above the soil surface after planting. Measure the height of the root ball from its bottom to the location of the topmost roots, or root flare, to determine how deep to dig the planting hole.

Once the shrub is set in the planting hole, remove all burlap, straps, and twine from the root ball. Leaving these materials on the root ball or in the planting hole will adversely affect the health of the shrub.

Bare Root: Bare root shrubs are field-grown plants where the soil is washed from the roots after they are dug from the field. Bare root shrubs have the fewest problems with circling roots and root flare identification since the roots are visible when purchased.

Planting the Root Ball

When planting shrubs, it is helpful to imagine this task as planting the root ball rather than the plant. Often, the planting hole for a new shrub is carelessly dug without much thought given to the root ball. The correct width and depth of the planting hole related to the root ball size are essential to its establishment and survival. Unfortunately, planting holes that are dug too narrow and too deep often leads to weak growth and the ultimate death of the plant.

The planting hole on this site is 2 times wider than the root ball. Soil amendments and composted pine bark have been mixed into the soil piled around the hole. On the sloped site, the top of the root ball is placed level with the soil on the upper side.

The planting hole on this site is two times wider than the root ball but no deeper than the height of the root ball. On the sloped site, the top of the root ball is placed level with the soil on the upper side of the planting hole.
Joey Williamson, ©2015 HGIC, Clemson Extension

Dig the planting hole two to five times wider than the root ball; the wider the hole is dug, the better. Roots will grow more quickly into loosened soil, thus improving the establishment time of the shrub.

The first step in determining the correct planting depth is to locate the root flare or topmost roots in the root ball. The topmost roots will be placed level with, or slightly above, the final soil surface at planting. Never dig the planting hole deeper than the height from the uppermost roots to the bottom of the root ball. Leave the soil at the bottom of the hole undisturbed, for a firm surface to place the root ball. Setting the root ball on loosened soil will cause the shrub to settle and sink too deeply.

In poorly drained or compacted soil, place the top of the root ball about 2 to 4 inches higher than the surrounding soil. Build the ground up around the root ball so that the sides are not exposed. Do not place additional soil on top of the root ball. This planting technique allows the roots to access oxygen in the upper surface of the earth, while also allowing excess water to drain away from the plant rather than collecting beneath it.

Since the plant is planted higher than the surrounding soil, the top of the root ball may dry out quickly in the summer. Monitor soil moisture and water accordingly.

Backfilling the Planting Hole

The soil used to fill in around the root ball is called backfill. As mentioned previously, the backfill should consist of only the loosened, unamended soil initially removed from the planting hole. The exception to using only the native soil for backfill is when amending the entire bed before planting.

Before backfilling the planting hole, break up soil clods that can create large air pockets around the root ball or hinder root growth and establishment. Place the plant into the planting hole with the topmost roots at or slightly above the surrounding soil level. Backfill the bottom half of the space around the root ball and pack the soil lightly. However, do not tamp the soil so hard as to compact it. Finish filling the hole in layers with the loose soil, gently firming each layer. Add a little water to make a mud slurry to help settle the soil and encase the roots. Remember to not place excess soil over the top of the root ball, as the root flare should be visible.

The amended soil is added to the planting hole in layers and firmed to eliminate large air pockets in the soil. On a slope, the excess planting soil is bermed up to the top of the root ball on the lower side of the hole.

Add previously amended bed soil or the native soil to the planting hole in layers and firm to eliminate large air pockets in the soil. On a slope, berm up the excess planting soil to the top of the root ball on the lower side of the hole. Joey Williamson, ©2015 HGIC, Clemson Extension

Mulching

Apply 2 to 3 inches of natural, organic mulch over the planted area. Do not let the mulch touch the trunk or stems, keeping it 2 to 3 inches away. Mulch piled against the trunk increases the chances of stem rot.

Use mulch to prevent weeds, retain soil moisture, moderate soil temperatures, and eventually improve soil organic matter content. Mulch also decreases the erosion of raised soil around plants that are planted above the soil level. Commonly used organic mulches include pine needles, pine bark, hardwood bark, wood chips, and partially ground leaves. For more information, see HGIC 1604, Mulch.

Watering

Proper water application immediately after planting is essential to the survival of the plant. Water well and slowly after mulching.

For the first year, direct water to the root ball because the roots will not yet have spread into the surrounding soil. Many plants die from too little or too much water during the first few months after planting. Plants in well-drained soil often get too little water, while those in poorly drained soil get too much water.

The surrounding soil is then covered with a 2- to 3-inch layer of mulch, and the plant is watered slowly to settle the soil.

Cover the surrounding soil with a 2- to 3-inch layer of mulch and water the plant slowly to settle the soil.
Joey Williamson, ©2015 HGIC, Clemson Extension

Become familiar with the planting site, and maintain even, consistent moisture (not saturation) in the root ball for the first few months after transplanting. Some areas dry out more quickly than others and will require more watering. Proper watering practices result in plants that establish more quickly, thus becoming more drought, pest, and disease resistant. For further information on watering newly planted shrubs and trees, refer to the fact sheet HGIC 1056, Watering Shrubs & Trees.

Maintenance

Proper shrub maintenance is essential for the long-term health of newly planted plants. However, following appropriate planting techniques and irrigation management are most crucial for initial plant establishment.

Para obtener la versión en español de esta hoja informativa, HGIC 1052S, Como Plantar Arbustos Correctamente.

If this document didn’t answer your questions, please contact HGIC at hgic@clemson.edu or 1-888-656-9988.

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