Plant Growth Management

By Patrick Anderson

Huge White Oak Tree by David Saddler
Huge White Oak Tree by David Saddler

Plant growth regulator.  That may sound scary to some, and counterintuitive to others.  Why would we want to intentionally stop a tree or shrub from growing, and how does that even work?  Believe it or not, it may actually benefit a plant’s health to slow its growth down. But, before we delve in to the specifics of plant growth regulators, or as I like to call them ‘plant growth managers (PGMs),’ it’s important to know that many of us come in contact with this technology quite often.

PGM History

PGMs first became popular in the floriculture industry to get uniform plants that would be merchantable when they made it to the garden centers.  Have you ever noticed your house plants start becoming leggy and a bit yellow after they’ve been in the house for a few weeks?  That is because the growth regulator applied before you bought them is wearing off.

Early versions of PGMs blocked cell division to accomplish reduced stem elongation (not unlike some herbicides).  Modern PGMs work within the plant to regulate the hormone (gibberellin) which is responsible for cell elongation.  This means the plant is still producing the same amount of cells, leaves, buds, etc. just extending 30%-70% less than normal.

Trees Need Pruning Less Often

This reduction in growth can lengthen time between pruning cycles for trees growing in close proximity to infrastructure, like that oak planted 10-feet from the corner of your house, those trees planted underneath the utility lines, or that hedge that needs to be trimmed a few times a year so you can see out of the front window.  Less pruning means less wounding for the tree (bonus for the tree), less work for you or a contractor (bonus for your wallet), and less ‘green-waste’ contractors have to dispose of (bonus for the environment).

Trees Handle Drought and Stress Better

Autumn Colors by Tiberiu Ana
Autumn Colors by Tiberiu Ana

PGMs also help a plant to mine more resources from the soil, and increases drought tolerance. While these growth managers are inhibiting the hormone responsible for tip elongation, they are encouraging the production of another plant hormone, abscisic acid, which increases fine root growth, reducing cell dehydration, and regulating leaf water loss.

PGMs can also increase the amount of chlorophyll the tree produces.  Chlorophyll is, of course, what gives a leaf its green color, and plays a major role in photosynthesis.  These effects of PGMs on plants are why many arborists are applying them to trees having just undergone, or which are about to undergo stress from construction activities.

Plant growth managers may seem a bit scary at first thought, but can be a great tree care tool when used correctly in our landscapes.  If you have more questions, ask your local Limbwalker, and they can guide you through the process of whether or not plant growth managers are right for your landscape.

If you have any questions about plant growth management, please call Limbwalker at 502-634-0400.