Salix babylonica is the scientific name for the weeping willow, a fast-growing, wide-spreading tree found mainly in the Northern Hemisphere. The willow family, a group of plants with the scientific name of Salix, has many uses that help sustain our environment as we know it. The willow is grown for biomass, for a renewable energy source, and its wood is used in the manufacturing of furniture. Willows even produce a charcoal used by artists, and their large sprawling root structure assists with soil stabilization and erosion control.
However, the most amazing product the willow family produces is root development hormones. The willow tree bark contains natural root development hormones that can be used in the vegetative propagation of a new plant. The willow’s hormones are so powerful that even a stem from a willow tree as large as a human thigh can take root if placed in damp soil. This magical root development hormone, called “Willow Water,” can be made from the branches of the tree.
In doing research on willow water, the research team first had to learn just exactly what is in the willow tree that gives it these immense powers of propagation. Two substances or chemicals that are present in the willow bark are Indole Butyric Acid (IBA) and Salicylic Acid (SA). These are naturally-occurring chemicals that have been used for numerous applications over the years. IBA is present in high concentrations in the actively growing branches of the willow tree, and stimulates rapid root growth and development. SA is a plant hormone that improves the plants’ defenses against disease. The combination of these two hormones allows for rapid root development and protection from diseases in one single application.
There are two separate methods for gardeners to extract these natural hormones and produce their own willow water for use in vegetative plant propagation. The first is the long soak. Small twigs are cut into pieces approximately one inch in length and placed in water to soak for between several days to a few weeks. Once the desired steeping is achieved, the water is simply filtered into a container, and it’s ready for use. The second method of willow water production proved to be faster. Willow twigs are cut into small pieces and placed in a container. Boiling water is poured onto the twigs which are allowed to steep for 24 hours while the water cools.
When preparing Salix nigra or black willow twigs for the extraction process, the research team decided to open the twigs with a few swings of a hammer. The thought process was to get a higher concentration of the natural hormones into our willow water. In addition, they wanted to know if there was a difference in the concentration of hormones between the ages of the twigs used. Younger new growth twigs were 1/4-inch diameter and less. The older twigs were ¼-inch to ½-inch in diameter.
Initial tests showed that pouring boiled hard tap water over the two sets of twigs resulted in initially darker-colored water with the smaller, young twigs. But after 10 minutes of steeping, the color of the willow water in each container was similar.
After 24 hours of soaking, the willow water was filtered to remove all twig material. The resulting brew was a deep dark brown color with a wet, woodsy aroma and a hint of sweetness.
Then the team looked at concentration levels of the home-brewed willow waters. The pH level test showed the solution had a level of 7.84, which was exactly the same as the hard tap water used. This indicated steeping the willow twigs did not make the solution more acid or more alkaline.
Next the Electrical Conductivity (EC) of the willow water was measured. The result was EC of 0.60 milliSiemens per Centimeter. With a reading this low, it can be determined that there are low amounts of ionized compounds, which means a low amount of salt compounds in the willow water.
Next came root development trials using cuttings from a gardenia mother plant. Gardenia jasminoides ‘veitchii’ can be difficult to propagate because they like humidity, warmth and a media that is moist but not totally wet. SteadyGROWpro plug media was used for the propagation tests. The use of rooting hormones speeds up the rooting process. Each gardenia cutting was approximately four inches long and made at a 45-degree angle above a leaf node.
Four sets of five gardenia cuttings were tested: one set with the larger old twig willow water, another set with the smaller young twig willow water and a third with a commercially sold liquid rooting hormone and the last group with hard tap water as a control set.
The commercially-sold liquid rooting hormone was diluted to have 1000 ppm of Indole Butyric Acid (IBA) and 500 ppm of Naphthalene Acetic Acid (NAA); gardenia cuttings were treated with a five-second immersion before sticking in the plug media. Although it is common to soak cuttings in willow water for 24 hours prior to sticking, for purposes of this test the gardenia cuttings were only soaked for one minute.
The cuttings stuck in the plug media were placed in a tray and covered with a domed lid to increase humidity. In the absence of a dome, frequent misting is acceptable. The tray was then placed under florescent lighting operating on a cycle of 16 hours on and then 8 hours off. No additional nutrients or treatments were applied to the gardenia cuttings.
The first inspection after seven days showed no wilting or stress on the cuttings. Moisture was present on the domed lid and on the media. The research team looked for the formation of a callus, a mass of non-specialized cells at the location of the cutting.
The control group in hard tap water showed no signs of callus formation. All five of the gardenia cuttings treated with the commercially-sold liquid rooting hormone displayed a callus.
The gardenia cuttings soaked in the small young twig willow water solution resulted in three of the five cuttings showing callus formation – a very encouraging result after only one minute of treatment.
The set treated with larger old twig willow water showed callus formations on four out of five cuttings. This told researchers the size or age of the twig being used may very well not be a factor in the potential of root development on cuttings.
The research team gave the gardenia cuttings a mist of untreated water and returned them to their domed tray. No conclusions were made after this first inspection of the gardenia cuttings except for the encouragement that nature has its own way of providing for itself.
After seven more days, the second inspection of the root development trials showed more encouraging results. In the control group, three of five cuttings showed a callus formation. The set of cuttings treated with a commercially-sold liquid rooting hormone maintained all five callus formations, with two showing root initiation.
The cuttings with small young twig water treatment showed four of five with a callus formation, while those treated with large old twig water showed all five of its cuttings having a callus formation.
A review of this second inspection revealed that improvements were made in all categories of the root development trials, and that the difference between the new growth twig and the old growth twig willow water is not an issue. After two weeks, willow water was living up to its reputation as a rooting hormone.
The third inspection of the willow water after another week went by produced surprising results. The control group and the commercially-sold liquid rooting hormone group displayed no improvement in callus formation or root initiation.
But the root development in the willow water groups was extraordinary. All five gardenia cuttings from both the new growth twig willow water and the old growth twig willow water showed callus formations as well as root initiation.
Over the next few weeks, the research team continued the willow water study to achieve healthy growing plants in all categories of the root development trials. They consulted with others who make their own willow water for vegetative propagation, who provided them with tips on improving performance. Their suggestions have been recorded and will be used in the next root development trials with a new brew of willow water.
The primary goal of these experiments was to show the science connection between natural chemistry and plant vegetative propagation. With the determination that the bark of the willow family (Salicaceae) of plants contains Indole Butyric Acid (IBA), which is a proven chemical in root development, along with other natural chemicals, the usefulness of plants and the propagation of plants to assist in the sustainability of the environment becomes evident.
With the simplicity of producing willow water and the proof of its benefits regarding plant propagation, the value of this natural resource is priceless.
Todd Trobaugh is a graduate of Ball State University and holds a Bachelors degree in Industrial Education and a Masters Degree in Educational Administration and Supervision. With over 18 years of education experience, Trobaugh was a teacher at Kokomo Center Schools and also the Assistant Director at the Kokomo Area Career Center both located in Kokomo, Indiana. Trobaugh is a Phi Delta Kappa professional education member and has been trained in Madeline Hunter Mastery Teaching.