Willow water rooting hormone is a simple DIY way to get some cheap rooting hormone. Lots of people use it for all kinds of cuttings and many claim that it works. In this post I will have a close look at the realities of willow water for rooting.
If you are not familiar with rooting hormones, have a look at this: Rooting Hormones – What Are They
Willows Root Easily
Take a piece of willow stem, stick it in the ground and it will root. A friend of mine wanted a rooted cutting from my corkscrew willow and I asked how big she wanted it. She said, “4-5 feet long”. I said, “that will never work”. Sure enough, I had no problem rooting it without any rooting hormone.
One reason it roots so easily is that it contains high levels of natural rooting hormones. It is basically a stick ready to root. One rooting hormone found in willows is indolebutyric acid (IBA), which is the main ingredient in many commercial rooting products.
Willows also contain salicylic acid (SA) which is similar to acetylsalicylic acid (ASA), the active ingredient in aspirin. Contrary to what many claim, this is not a rooting hormone, but it can help rooting hormones be more effective.
Making Willow Rooting Hormone
There are numerous recipes on the internet for making willow rooting hormone, but they basically consist of taking various parts of a willow tree or shrub, crushing the material and steeping it in water. The IBA and SA leech into the water which can then be removed and used to root cuttings.
Some people leave the cutting in the water until it roots, and others just dip them for a few minutes before sticking them into rooting media.
It is claimed that the auxin IBA is most concentrated in new shoots and especially shoots harvested in late winter or early spring.
Most Cuttings Root Easily
The reality is that most cuttings that the average gardener tries, root easily without any rooting hormone. Many plants root in just water, and others in standard rooting media like sand or perlite.
A common claim for willow water rooting hormone is that it “is most effective on moderately easy-to-root plants”. But this kind of cutting does not need any rooting hormone!
Limitations of Anecdotal Evidence
You will find two kinds of reports on the net. One type is mostly a DIY discussion of how to make and use willow water. They rarely provide any evidence or examples that show it works. The second kind of report discusses how it worked for a certain type of plant. These usually don’t provide details of how the water was made or which kind of willow was used.
Neither of these reports are of much use to validate the effectiveness of willow water because they are not complete and because they rarely include controls. Without proper controls you can’t reach any conclusion.
Concentration of IBA in Willow Water
Willows contain IBA, but how much IBA ends up in a homemade willow water hormone solution?
It turns out that IBA is not very soluble in water, with a solubility of 250 ppm (at 20 °C). This is the highest concentration that you can get, assuming perfect extraction.
For herbaceous and softwood cuttings, commercial IBA rooting hormone is applied in concentrations of 500-1,500 ppm. Rates between 1,000 and 5,000 ppm are used for semi-hardwood cuttings and 10,000 ppm is used for hardwood cuttings.
Clearly, the amount of IBA in homemade willow water is significantly below the recommended levels. It might help for softwood cuttings, but will not be effective for semi-hardwood, or hardwood cuttings.
Many recipes recommend the dilution of willow water before use, which decreases its effectiveness even more.
IBA is more soluble in alcohol so it would be better to extract the hormone using an alcohol-water mixture, but nobody recommends this.
Concentration of IAA in Willow Water
IAA is also a naturally occurring rooting hormone found in willows. It has a higher solubility of 1,500 ppm, which would be high enough. IAA is not used in commercial products because it is not very stable.
Effects seen from willow water may be due to IAA.
Science on Willow Water
This study looked at rooting cannabis cuttings with two rooting gels; 0.2% IBA gel (EZ-GRO Inc.) and 0.2% willow extract rooting gel (EZ-GRO Inc.). The results show that the willow extract far under performed IBA in both the number of rooted cutting and the quality of cuttings. Unfortunately, a control with no rooting hormone was not done, so we don’t know if the willow extract was better than no hormone at all. Also note that (a) this was a commercial willow rooting gel, not DIY willow water and (b) it seems the company no longer sells this product.
A report looking at rooting apple cuttings found that willow water increased the number of rooted cuttings to 96%, but the control using only water had a 92% success rate.
Using willow water to water after applying standard rooting hormone resulted in more roots and longer roots using four different types of cuttings.
Olive cuttings can be difficult to root. When they are treated with IBA and followed with a soak in willow water, it was found that willow water made from the bark of weeping willow, did increase the rooting rate, but soaking in water made with wood, leaves or shoots had no effect.
There is limited science looking at the effectiveness of willow water, and what is there does not support the idea that it effectively initiates roots. It may contain low levels of hormone which might augment the natural hormones in cuttings and it may provide some benefits once rooting has started but the science suggests this effect is limited, if it is there at all. It is not a good rooting hormone.
I suspect the myth of willow water was born out of sound science; willows root easily and that they contain rooting hormones. From there, a leap of faith concluded that homemade willow water would work as a rooting hormone. This idea is then bolstered by gardeners who try it and claim it works, without ever running controls.
Given the lack of evidence that willow rooting water works, and the fact that it is not easily produced, it seems to make more sense to use commercial products that are easy to use, and are proven to work. For a few dollars you can buy enough rooting hormone powder to last 10 years or more.