The root structure

As growers, purchasers and users of plants, we make frequent judgments on plant quality looking only at the stem, leaves and form. What about the other half of the story? What about the roots? When was the last time you looked at the roots of the plants you purchased or planted?

You might ask, “how do I judge root quality?” Quantity, health and distribution are several important considerations, which are often easily assessed. I would like to unearth the often-overlooked aspect of root structure. Proper root structure is very important, especially for tree species. Anyone planting a tree is expectant and hopeful that it will grow large, tall and old. A big, tall tree needs proper lateral anchor roots to keep it standing strong through the elements for many years. Unfortunately the nursery industry hasn’t adopted systems that manage these important anchor roots well.

Dr. Ed Gilman from the University of Florida has been studying roots and root structure for over 30 years. His research is remarkable and very practical. He and his team have gone to great lengths to test the impacts of poor structure resulting from nursery practices; even to the point of building a 3000hp jet engine powered portable wind tunnel to test anchorage and stability of large trees in their long term trials.

Dr. Gilman points out that “most of the main roots of a tree are set in the first 2 to 3 years of its life.” That is an important thing to know. More importantly, have the trees you are planting been grown with this in mind? Poor root structure from nursery practices leaves a damaging “imprint” on the plant. Perhaps the greatest culprit of poor imprints comes from growing in hard-wall, smooth sided pots and trays. When roots reach the hard wall of the container they are redirected. Roots redirected sideways can spiral around creating an imprint known as root circling. Roots directed downward by the container wall aren’t desirable either. Lateral anchor roots are formed by a tree to be its primary support mechanism. Being turned downward compromises their ability to perform their function well.

These imprints don’t simply correct themselves after planting. They remain permanent as part of the structure of the tree. Imprints from circling roots can even later girdle the stem and kill the tree.

This problem and its implications aren’t new to the industry. Over the past couple decades a number of pot and tray manufacturers have developed systems to try and deal with this challenge. Some of these have brought modest improvements, but few have provided a really good solution. No doubt, growing within walls without leaving an imprint is difficult.

Coming to this realization 10 years ago was humbling for us at Verbinnen’s Nursery. It was the beginning of numerous trials with our trees. We now have settled on a system that uses coconut coir liner pots that air prune the roots when they reach the sidewalls and bottom of the pot. Air pruning roots is a more natural way of pruning that additionally induces further root initiation within the root ball. This creates a more dense, fibrous root system, allowing for quicker rooting out after planting. Using coir pot liners has become our production standard for all of our tree species propagated in plugs trays. Growing in pots while maintaining good root structure is an area we are continuing to work on.

Here is the takeaway: Consider the root structure of the trees you are buying and planting. Look for imprints where roots have been redirected. Lastly, I highly recommend visiting Ed Gilman’s website with the University of Florida. They have done a great job at making their research publically accessible. They also provide helpful information on what can be done to deal with poor root structure imprints that are accessible.

Whether you are planting one tree or a thousand, proper root structure should be considered to give what is needed for a long, healthy, stable life.