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Container types

Introduction

Containers are manufactured in a variety of shapes and sizes and are constructed from many different materials. (See bottom of this page for a list of manufacturers.) These include plastic, paper, aluminum, containers for growing treesfabrics, wood, and peat. Roots are deflected by container wall down and around the container edge. This can develop into serious root defects if trees are left in the container too long. Specially designed containers reduce but do not eliminate the amount of circling roots (some are shown at right). Trees grow at about the same rate in the various containers. Trees grown in containers should be root pruned to remove circling and descending roots each time the tree is potted to a larger size (See: Details root pruning). This results in a root system with straight roots radially distributed around the trunk. If not removed each time the tree is potted to a larger size, severe root defects could develop making the tree a cull (See: Details of root defects).

See: Root growth in containers - photos and research, and photos

Trees perform equally well from most container types tested to date following installation into the landscape if irrigation can be provided regularly after planting (Marshall and Gilman 1998; Struve 1993). However, some container types perform better than others if irrigation is limited after planting (Gilman 2001). (See: Details of performance after planting).

Here is a brief discussion of the various container types:

tree with circling roots1) Tall-and-narrow containers: Trees from containers that are tall and wide might survive better than those from other container shapes in well-drained, droughty sites with little irrigation. While roots in the top portion of the root ball may dry out, those at the bottom have a better chance of elongating into the landscape soil before drying up and dying (Gilman and Beeson 1996). In compacted or poorly-drained sites, roots at the bottom of a tall root ball may not help the tree become established because they often die from lack of oxygen (Gilman et al. 1987). A short and wide container (low-profile container) might be better suited for sites with poor drainage.

2) Short and wide (low-profile) containers: Circling roots are less of a problem in a wide container because if they do develop they are located farther from the trunk (Marshall and Gilman 1998). However, like all other plants, circling roots may be present close to the trunk if the tree was in a smaller container when it was younger. Trees planted into well drained soil from low-profile containers are more susceptible to draught following installation than deeper root balls (Marshall and Gilman 1998) However, in poorly drained and compacted soils, they should perform very well because roots are located closer to the soil surface where air is plentiful. Roots toward the bottom of deep containers (more than about 24 inches deep) may not survive planting in compacted or poorly drained soils due to lack of oxygen at these depths.air pruined plastic containers

3) Air-pruned containers, plastic: Some containers are designed with many holes in the sides and bottom. Some of these are bottomless, others have large openings in the bottom. Manufacturers suggest and research basically supports that roots at the outside edge of the root ball are pruned and branch because their tips are killed by air entering the holes (Privett and Hummel, 1992). Few roots are evident on the outside of the root ball; deflected roots on these containers tend to be positioned about an inch or so inside the periphery of the root ball.

Air root pruning reduces circling and descending roots, and according to manufacturers creates a denser root ball on some species (Whitcomb and Williams, 1985). Reduction (not elimination) of circling roots is common, but research studies show no increase in root density (Newman and Follett 1987;Beeson and Gilman 1995; Marshall and Gilman 1998; Gilman 2001). Some containers air prune more than others. The reduction of circling roots reduces the likelihood of roots strangling the trunk as the tree grows older. Trees transplant about the same regardless of container type (Marshall and Gilman 1998; Gilman 2001; Gilman et al. 2002).

4) Air-pruning containers, paper: This new product is crafted of very thin paper held by an open plastic mesh. Roots grow to the edge of the container (the paper) and many grow through the paper and die. This prunes (kills) the roots encouraging new roots to grow behind the pruned portion of the root.

5) Ribbed container: Ribs in a variety of configurations along the insides of containers are designed to prevent roots from circling the outside of the root ball. Roots are often deflected down vertical ribs to the bottom of the container. Some of these containers also have holes along the ridges and at the bottom. Trees from ridged containers should transplant similar to those from traditional, smooth-sided containers, although detailed research is lacking. The advantage of purchasing trees grown in these containers is that there may be fewer roots circling the outside of the root ball, especially near the top.

6) Copper-coated containers: Some container insides are coated with a copper compound (Spin OutTM, Griffin Corp., Valdosta, GA). Fewer circling roots are produced on trees in these containers if trees are not left in too long (Struve et al. 1994). Early tests indicate that following planting into the landscape, root elongation and growth of the shoots and trunk is similar to or slightly greater than growth on trees from conventional, smooth-sided containers (Struve 1994; Marshall and Gilman 1998; Gilman 2001).

7) Wooden box or metal container: There is no data to suggest that trees grown in wooden boxes or metal containers transplant any differently than those from other containers.

8) Peat pots: The bottom portion of a peat pot can be left on the root ball at planting. The dried top portion should be removed to prevent moisture from wicking out of the root ball.

9) Non-ridged containers: Trees are occasionally grown in substrate or soil placed inside a flexible container made from fabric, mesh, plastic, or other material. Trees from these containers should transplant as traditional container-grown trees provided the root ball remains intact. Root balls may be more fragile in these devices than more ridged containers.

Container manufacturers: Beaver Plastics (www.beaverplastics.com), Belden Plastics (www.beldenplastics.com), Blackmore Plastics (www.blackmoreco.com), Gage Industries, Inc. (www.gageindustries.com), Keiding, Inc. (www.keiding.com), Landmark Plastic Corp (www.landmarkplastic.com), Monarch Manufacturing, Inc. (www.monarchmfg.com), Nursery Supplies, Inc. (www.nurserysupplies.com), PioneerPot.com, Root Control, Inc. (www.treebag.com), RootMaker Products Co. LLC (www.rootmaker.com), Sierra Horticultural Services (www.sierrahort.com), Stuewe & Sons, Inc. (www.stuewe.com), Western Pulp Products Co. (www.westernpulp.com).