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Tuesday, August 20, 2013

Slow Growth Can Be a Sign of Poor Plant Selection

Q. We notice that some of our trees don't seem to be rooting into the soil properly.  We assume it's due to improper root ball preparation or girdling roots. Our test to see if the tree has rooted after at least one growing season is to bend the tree trunk back and forth.

            If the root ball under the soil easily moves when the tree is pushed, we assume that the tree has poor or little rooting into the surrounding soil.

            We also believe it’s a permanent problem, not correctable and thus the tree needs to be replaced.  Any suggestions for making a better evaluation and discovering this potential problem before planting?

Root circling from container plant

A. Poor tree establishment due to girdling or circling roots is a major problem with many plants, not just trees. This problem can begin at a very early age, even when it is just a seedling. But if plants are grown too long in containers then the problem can become worse.

            Once roots begin growing in circles inside a container the problem can no longer be corrected, even at planting time. This problem should be identified before purchasing and the plant rejected.

Roots seen circling when pulled from container

            Generally speaking, plants which are very large compared to their container have a significant chance of having girdling roots. Buying oversized trees in containers is no bargain.

             When buying a container plant that I can lift, I will gently pull the plant a few inches out of the container and inspect the roots for circling. This includes bedding plants! Secondly, I select trees that are not oversized for their container. Here is a case where smaller plants of the same sized containers will out-perform the larger ones.

Surface roots from circling container roots. Notice how the trunk lacks "flairing" at the soil surface on one side of the tree. One way to detect these types of roots when they are present but hidden below the soil surface.

            Plants in containers should usually root, or become established, in one full growing season. Large trees, such as those planted from boxes, may take two to three seasons. Malformed, girdling roots will continue to circle in the same pattern once they are planted in the ground. Because of this, they will never grow beyond the planting hole after planting.

            In other words, they stand a good chance of never getting established. If they never grow beyond the planting hole, the tree roots will never be strong enough to support the tree when it gets bigger.

Scoring the rootball can sometimes help repair girdling roots, if they are not extensive, when planting. This NOT a substitute for good plant production practices or poor plant selection.

            A sign that a tree may have circling or girdling roots after it has been planted is stunted growth. This stunted growth can take years after planting before it appears. It is a good idea to identify trees that have this problem early in their development.

            Another indicator is the presence of girdling roots on the soil surface and a lack of trunk flaring at the soil surface but this can take years to develop.

            Your method is a good one for determining if trees have not become established after planting. Once the establishment period is over, I use the same procedure that you prescribe (bending the trunk) to determine if there are girdling roots down there or not.

            Boxed trees are replanted from containerized trees. Normally, container trees are staked as soon as they are planted in a box. However, if the container tree had girdling roots then they will continue to girdle and never establish in the box.  

            There are three other things that can cause poor rooting into the surrounding soil as well; poor hole/soil preparation, improper staking or not staking after planting and watering too close to the tree.

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