4/24/2025 - By Dr. Aaron Palmateer

Recent trials with Dr. Xunzhong Zhang, Virginia Tech, have shown that Azo Root™ paired with Harrell’s EarthMAX® Organic produce noticeable improvements to plant health, leaf color, photochemical efficiency, leaf chlorophyll, and root growth/biomass.

Azo Root™, the revolutionary product from Harrell’s and 3Bar Biologics has proven to be an extremely beneficial tool in the microbial biostimulant space. When Azo Root™ is paired with EarthMAX® Organic, the combination opens doors to growth that were previously much more difficult to achieve.

Dr. Zhang’s objective with the study was to evaluate the effects of these products on rooting and physiological responses in Poinsettia. Treatments were applied to cuttings (callused and un-callused) as a soil drench at 2 gal per 1000 sqft. Poinsettia plants were grown on a bench in a greenhouse with a mist system under shade and then on a bench in a greenhouse environment with minimal/mild induced stress. The poinsettia plants were fertilized at 0.1lb N/1000 sqft from 20-20-20 fertilizer plus micronutrients weekly.

The beneficial effects of Azo Root™ and EarthMAX® Organic treatments on plant health and leaf color were observed 14 days after initial application with greater ratings for both compared to the control on days 28, 42, and 56, respectively. Treatments with the combination had better plant health and leaf color than the treatment with Azo Root™ alone at days 42 and 56. Azo Root plus Soil Enhancer and Azo Root™ plus EarthMAX® Organic improved photochemical efficiency as early as 14 days and on days 28, 42, and 56 after initial application. On day 56, all treatments had greater PE relative to the control.

Treatments did increase chlorophyll content relative to the control, but the difference was not significant. The combination of Azo Root™ and EarthMAX® Organic consistently improved root biomass, surface area, volume, and viability relative to the control.

In summary, Azo Root, EarthMAX Organic, and Azo Root plus EarthMAX exhibited beneficial effects on plant health, leaf color, and photochemical efficiency in Poinsettia during rooting and growth periods. The combination also improved root growth and viability relative to the control. Overall, Azo Root plus EarthMAX exhibited greater beneficial effects relative to Azo Root alone and control. Based on the results from three replications of each cultivar, we found that uncalloused cutting “Red Premium” had great root surface area and volume when compared to callused cutting “Ice Crystal.”

If you would like to learn more about these research trials or any of the products mentioned, reach out to your local Harrell's representative, and check out our blog page for all of the latest updates.