Simple nutrient adjustments can replace chemical rooting agents in hibiscus production
Researchers from the Department of Food Science at Aarhus University show that the choice of nitrogen form can double root growth in hibiscus cuttings – an important step toward more sustainable and legal plant production in Denmark.
Danish nurseries are not allowed to use auxins (plant hormones) to stimulate rooting, which makes propagation of ornamental plants such as hibiscus challenging. However, new research from the Department of Food Science at Aarhus University (AU FOOD) shows that a simple change in fertilizer composition can significantly improve rooting – without the use of chemical additives.
Effective root growth with ammonium sulfate
In an experiment with two Hibiscus varieties, ’Petit Orange’ and ’Adonicus White’, researchers from AU FOOD tested the effect of different nitrogen forms on the ability of cuttings to form roots.
The experiment was conducted under controlled growth conditions in an aeroponic system (a method where plants grow without soil and receive nutrients through a fine mist). Concentrations of ammonium and nitrate were supplied precisely and kept constant, since nitrification (the bacterial conversion of ammonium to nitrate) is not significant in such systems. Furthermore, the absence of a substrate (a material such as soil or rockwool that plants usually grow in) made it possible to observe and measure root formation and development with high precision.
The results showed that ammonium sulfate ((NH₄)₂SO₄) could double the number of cuttings forming roots and, in some cases, more than triple root growth.
“We see that targeted ammonium supply can promote rooting almost as effectively as chemical rooting agents – but in a natural and legal way,” says Associate Professor Ivan Paponov from AU FOOD.
In practice, however, the use of ammonium is more complex. In the aeroponic experiment, the plants received ammonium only during the first seven days, when new roots began to form. Afterwards, they were transferred to control conditions. This short treatment was sufficient to stimulate rooting.
In systems containing a substrate, ammonium can instead be converted to nitrate at different rates depending on the growth conditions. Therefore, more research is needed to understand how changes in nitrogen form, together with substrate properties, affect rooting under commercial production conditions.
One possible explanation is that ammonium acidifies the root environment, which promotes root initiation. This makes nutrient management a promising alternative to chemical growth regulators in ornamental plant production.
New opportunities
The results can directly benefit growers who wish to improve the propagation of ornamental plants in a sustainable and compliant way. The research also opens up new opportunities to adjust nutrient strategies for other species where root formation is a bottleneck.
Future studies highlight the need to investigate how different nitrogen forms and substrate properties influence rooting under practical horticultural conditions. Similar strategies may also be applied to other ornamental species where rooting is often a challenge during propagation. However, such studies will require additional funding to be carried out.
Contact Information & Scientific Declaration
| CONTENT & PURPOSE | |
|---|---|
| Study type | Since Danish nurseries are not allowed to use auxins to stimulate rooting, the study investigates how different nitrogen forms can improve root growth in hibiscus cuttings. Through controlled experiments and collaboration with horticultural partners, the goal is to develop simple, permitted, and sustainable methods for improved plant propagation. |
| External partners | HortiAdvice, Graff Growing A/S |
| External funding | This project was carried out at Aarhus University, Department of Food Science (AU FOOD), in collaboration with HortiAdvice and Graff Growing A/S. The experiment is part of the GUDP project FUTFLOR. |
| Potential conflicts of interest | The project was carried out in collaboration with HortiAdvice and Graff Growing A/S. No conflicts of interest are declared. |
| Contact information | Ivan A. Paponov Kimie Kongsøre |