Importance of Root Structure

Back to our Roots

Above: Maple tree seedling grown in air-pruning coco coir pot

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 closely 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 has not 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 3000 hp 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 two to three years of its life.” This fact is important. The trees you buy should have been grown with optimum root quality in mind. Poor root structure from nursery practices leaves a damaging and lasting ‘imprint’. 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. When such tree seedlings are planted, much of the new root growth is at the bottom of the plug, well below the soil surface.  In less than ideal soil conditions, low-down roots may struggle with compacted soil with low aeration.

Above: Downward deflection of roots from conventional tray are not good

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

Dr. Glen Lumis, professor emeritus at the University of Guelph, has spent many years studying nursery-grown roots.  He, like many others, stress “roots straight out from top to bottom”.  He also says “imperfect, misdirected roots, particularly for trees planted in less than ideal sites, result in slow establishment, tree decline and potential failure”.

The key to a good root system is to perfect it not correct it at planting.

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

At our nursery, we have begun numerous trials to perfect our roots.  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 type of pruning 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 our tree species propagated in plug trays.

Above: Proper natural lateral root structure of an oak tree seedling grown in a coco fibre pot

Above: This three year-old maple tree was started in a coco coir pot

Proper forethought and attention to root structure is an integral part of reaching our long-term goals in restoration.  Have you been considering root structure? We have. Why? Because it’s our job to provide you with good quality trees full of potential for a well anchored future.

For further learning on root structure, we highly recommend visiting Ed Gilman’s website with the University of Florida. They have done a great job at making their research publicly accessible. They also provide helpful information on what can be done to deal with poor root structure imprints that are accessible.