With the return of longer days, a gardener’s mind starts to turn to plant propagation: starting plants from seeds … and also cuttings. Amazingly, it’s possible to multiply the vast majority of pluriannual plants (houseplants, perennials, shrubs, trees, vines, etc.) by stem cuttings, but some, especially those with somewhat woody stems, are often reluctant or slow to produce roots. In these cases, you can apply a rooting hormone and it will usually stimulate faster rooting and even ward off root rot in the process.
There are commercial rooting hormones, of course, in powder, gel or liquid form, and they are very effective, but you can also make a homegrown hormone from willow (Salix spp.) stems.
Willow stems emit an auxin called IAB (indolbutytric acid), a hormone that naturally stimulates roots to grow. In fact, commercial rooting hormones are essentially made up of synthetic forms of IAB. In addition to rooting hormone, willow stems release salicylic acid (AC), which slows the healing of the wound, allowing the sap to continue to circulate … and giving roots more time to develop.
You probably already know salicylic acid for its effect in humans: slightly modified, it is ASA (acetylsalicylic acid), better known as aspirin.
Willow Water Recipe
There are several ways to make willow water, but the easiest probably just to crush a few dozen freshly cut willow twigs with a hammer and let them macerate in a container of water for 24 to 72 hours. This will release IAB and AC into the water. Now, filter the resulting liquid and pour into a glass. Place your cuttings in this liquid in a warm and brightly lit spot and wait patiently. As soon as you see roots starting to appear (at first they’ll look like small white or yellow bumps on the stem), transfer them to potting soil.
Do not wait until the roots are long and intermingled! (To understand why, read Starting Cuttings in Water: Not Such a Good Idea.) Cuttings made in water should be moved quickly into a terrestrial environment (i.e. into a potting mix) as soon as roots appear, otherwise there is a serious risk of losing them.
You can make rooting hormone from any willow, both shrubby and tree species, but the auxin is most concentrated in new shoots and especially shoots harvested in late winter or early spring. So, the rooting hormone you produce will be at its most efficient at that time of year.
Willow Water: Moderately Effective
Willow water is most effective on moderately easy-to-root plants, generally softwood and semi-hardwood cuttings. It is rarely effective on cuttings that have the reputation of being hard to root, as is the case with most hardwood cuttings, notably those taken from lilacs, fruit trees and conifers.
For such “difficult cases,” you’ll find you get much better results with commercial rooting hormones of an appropriate strength.
And of course, “easy-to-root” plants, usually those taken from herbaceous (non-woody) plants such as coleus, chrysanthemums and philodendrons, don’t need any extra hormones at all, be it willow water or commercial hormones, because when you put their cut branches in an appropriate environment, they quickly produce their own rooting hormones.
To learn more about taking cuttings, read Rooting Cuttings Step by Step.
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I have looked for a reference to support the fact that willow water works for rooting, but have not found one. I am unconvinced that it works excepr in cases were the cutting would root on its own.
I’ve found a few (here’s one: http://www.citruscollege.edu/stem/summerresearch/Documents/Posters/2013/WillowWater.pdf) that suggest modest results with willow water on certain plants. However, I tried to write the piece in such a way as to moderate expectations. My hope is that serious gardeners will understand that it’s easier to turn to commercial rooting hormones when dealing with difficult-to-root plants… and not waste their money on hormones of any kind for easy-to-root plants.
That reference looks at the effect of willow water on cuttings that have been treated with a commercial rooting hormone. It does not demonstrate root initiation due to willow water.