Design guidelines for tree quality and planting - tree trenches and tree boxes

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Trees can be purchased in many different forms. Gillman and Johnson (1999) describe some of the various forms as follows.

Bare Root. Bare root plants are dug from nursery fields in the fall or spring. Soil is removed from the roots, and plants are held in humidity and temperature controlled storage over winter. They must be planted in early spring before growth begins. Because many roots are cut during field digging, bare root plants suffer severely from transplanting shock. Bare root stock is normally the least expensive, but if handled improperly, can have the highest mortality. When handling or transporting bare root stock, keep the roots moist and protected from sun and wind at all times.
Packaged. Packaged trees and shrubs are bare root plants with their roots packed in moist material such as peat moss or shingle tow. Plant them in early spring before growth starts. Keep packing materials moist, and the package cool and shaded until planted. These plants should be treated as bare root plants.
Field-Potted. Field-potted nursery stock are field-grown plants dug with a ball of field soil intact which is then placed as is, in a container. These plants should be sold and planted during the spring, as field soil will not provide good plant growth in a container. It is important that the root ball be disturbed as little as possible during the digging and planting process.
Containerized. Containerized trees and shrubs are dug from the nursery in the spring or fall as bare root stock, placed in a container with a special growing medium, and sold in the container. If containerized in early spring, most plants will be sufficiently established in the container and can be transplanted in late spring, summer, or fall. Roots must be established in the container and hold the media together before transplanting. Do not completely break up the root ball at planting time, but do cut any circling roots prior to planting. The tighter the root ball, the more the root system should be disturbed.
Container Grown. Container grown stock has been growing in a container throughout most of its production. Because the roots of these plants are not disturbed at the time of planting, container grown plants suffer little transplant shock and may be planted at any time during the growing season. Plants that have outgrown their containers may have deformed root systems, which can result in girdling roots. Large plants may be root bound in the container. The root ball of these plants must be torn or cut open [or box cut] to eliminate subsequent circling or girdling roots (Figure 3).
Balled and Burlapped (B & B). Balled and burlapped trees and shrubs are dug with a firm ball of soil around the roots, and held securely in place with burlap, twine, and sometimes a wire basket. A broken, damaged, or dry soil ball can result in serious damage to the roots. The stem should not wobble in the soil ball. Because of the weight of the soil ball, B & B trees can be difficult to transport and plant without special equipment. B & B stock is often the most expensive, but if handled and planted properly, is as reliable as container grown stock. Always lift B & B plants from beneath the ball, never by the stem. B & B stock can be planted in spring, summer, and fall.
Tree Spade. Larger plants are often moved with a tree spade—a machine that digs a mass of soil including the plant and some of its roots. The plant and root ball may stay in the machine until it is planted into a pre-dug matching hole, or it may be placed in a wire basket lined with burlap. The size of the root ball is critical and species dependent. An experienced machine operator can make the difference between success and failure. Matching soils from the digging site to the planting site is also important, as is compaction within the planting hole. Roughing up the sides of the hole can offset some of this compaction. Plants can be moved in most seasons with a spade, although plants dug in summer and early fall should have an oversized ball and receive special attention relative to species, condition, handling, and irrigation.” (Gillman and Johnson 1999, italics added).
Gravel Bed Method to market bare root trees. The Gravel Bed Method is a method of handling bare root nursery stock in which dormant plants are placed in an irrigated bed of gravel in the spring with their roots submerged in gravel. These trees are held for up to a year before planting bare root (in full leaf) in the landscape. It is a lower cost method to grow trees that extends the planting season of bare root stock. Root growth in gravel is very extensive and point fibrous and, unlike with bark mulch, sawdust or sand, few roots are damaged when plants are removed from the gravel. The gravel bed method also greatly minimizes the risk of girdling roots compared to containerized and B&B trees. For more information on gravel beds, see All you need to Know about Community Gravel Beds (Busiahn and Peterson 2013).

It is recommended that trees are inspected by the Owner or Project Landscape Architect prior to digging at the nursery where applicable.

Many tree material and planting specifications have already been developed by others. Many municipalities and jurisdictions, for example, have developed their own tree material and planting specifications. Many university extension services and tree organizations also provide tree planting guidelines. The tree material and planting guidelines below were developed based on experience and research by the contracted and technical teams for this project, combined with the resources listed in the references section. Additional guidance regarding tree planting is available in the references section below, as well as at the following 2 websites:

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