RPM® and Restoration
reprinted from PDF: HRN Restoration News, Part 1
by John Nitta
One fundamental step in the RPM® process is early root pruning. While in the seed or cutting flat, when roots are initiating, roots head down and hit the bottom of the flat, which is no more than two inches deep. As the roots emerge from the bottom of the flat, the tips hit the air, and are “air-pruned”, that is, they die back at that point. This tip die-back causes the root system to initiate more roots higher up, and these in turn seek the bottom and again are air-pruned.
A question we often get is, “What happens to the taproot?” As the taproot is a single, perhaps first root to hit the bottom, it is the first to get pruned. Thus, the taproot is the first to go. There are many theories around the taproot, such as its functions for anchorage and for seeking water deeper in the soil. Root systems have been categorizedas being “taproot”, or “fibrous”. So, what does the RPM process do to the plant’s natural tendency to be a “taproot” or “fibrous” root system?
Recent observations have shown that the taproot is a temporary root. Deep rooted plants such as mesquite in Southwest arid climates may have roots going 40 feet deep to find water, but these are seeker roots, not a traditional taproot that is thought of for anchorage and a pipeline for bringing water up to the top. More important for anchorage and stability are “brace” roots. These are high scaffold-type major roots that flare at the crown of the plant, and become the main “anchor” roots. On mature trees, most of the major roots for stability and feeding are found in the top 12” of soil.
Arborists know the important of protecting roots within the dripline area. A formula for protecting trees, as developed by Matheny & Clark, called Tree Protection Zone (TPZ) is based on the tree’s inherent tolerance, vigor, environmental factors, and more to determine protection zones for fencing off during construction. Of course, on restoration sites you wouldn’t expect any heavy equipment in the area! Nonetheless, the flaring out and wide shallow distribution of roots is what RPM promotes, and thus, nursery plants grown with the higher fibrous root systems have a much higher rate of establishment and survival, which for restoration purposes, is of utmost importance!
RPM® promotes development of strong brace roots for superior stability.
Image courtesy of RPM Ecosystems