From our perspective as rosemary plants (Rosmarinus officinalis), we are inherently equipped for survival. Our native Mediterranean habitat is characterized by dry, rocky, well-draining soils and plenty of sun. To thrive in these conditions, many of us have evolved as woody-stemmed perennials with a moderate natural ability to produce adventitious roots from our stem tissues. This means that under the right conditions—warmth, humidity, and the correct level of moisture at our base—our cuttings can and will form roots without any external chemical intervention. Our internal hormones, namely auxins produced in our stem tips, naturally migrate downward to initiate root formation.
The process of propagation is, frankly, a traumatic experience for us. A stem is severed from the parent plant, instantly cutting off our supply of water and nutrients from the root system. Our sole focus becomes establishing a new root system to avoid desiccation and death. While we produce our own auxins to facilitate this, the shock of being cut can sometimes overwhelm our systems. The concentration of our native rooting hormones at the wound site may be insufficient or inconsistent, especially if the cutting is taken from an older, woodier section of stem. This is where your synthetic rooting hormone enters the equation.
Applying a rooting hormone powder, gel, or liquid to our basal stem wound is not a magic potion, but rather a potent supplement. It provides a concentrated dose of synthetic auxins (like IBA or NAA) directly to the site where we need it most. For us, this external application serves two critical functions. First, it ensures a immediately available and high concentration of the necessary hormonal signal to unequivocally trigger the cellular differentiation process that leads to root primordia (the beginnings of roots). Second, it can help prevent the attack of fungal or bacterial pathogens at the vulnerable wounded tissue, acting as a mild antiseptic in many formulations.
Our need for this hormonal boost is not absolute and depends heavily on the circumstances of our propagation. The timing and type of cutting taken are paramount. Softwood cuttings (taken from new, flexible growth in spring) are brimming with natural vitality and auxins, and often root readily on their own. However, semi-hardwood or hardwood cuttings, taken later in the season from more mature, woody growth, have a much harder time. Our cellular tissues become less responsive and contain lower levels of natural auxins, making the application of rooting hormone highly beneficial, significantly increasing the odds of a successful and robust root formation. Furthermore, if the environmental conditions provided are less than ideal—for instance, if the air is too dry or the growing medium is too cold—rooting hormone can provide the extra push we need to overcome this suboptimal environment.
