It is the middle of winter. And you are thinking about trimming some of your trees. As you start clipping away, you realize that the tree has nice compact growth. Internodes are short. And the species is nice too. It is a shame to just toss away the branches, right?
Fortunately, several species of trees can be propagated by winter cuttings, or hardwood cuttings. So if you are trimming your bonsai, and you would like to propagate some of your trees, here is how you go about it.
It is important to realize that not all species work equally well, and some may not work at all. However, species that respond really well to this are from the following families: Forsythia, Cornus, Juniperus, berberis, buxus, Ilex, Ligustrum, Taxus, Malus, Lonicera.
Some species grow so well from cuttings, that you can take very thick cuttings. Species such as willow, olive and pomegranate will root at almost every size as long as the right conditions are provided.
However, in my case, I was trimming maples when I thought to take some cuttings. These are not known for successful rooting of hardwood cuttings. However, I have heard from some persons that it can be done.
Furthermore, I had a bunch of Prunus Mume branches. I do not recall any success stories growing these from mature branches or even in general, hardwood cuttings. But.. having the material there, I decided to try whether it works for me. So this is what I did.
Getting the material
With disinfected clippers, I took the ends of healthy branches of my Acer palmatums (Which include the wild green version, deshojo and arakawa). This was on a day with night time temperatures around 0 Celsius, and very high humidity.
Taking the hardwood cuttings
Next, I brought them to my workbench, where I clipped them into section of 5-10cm long. Directly after clipping each cutting was dipped in a rooting gel called clonex. Once all cuttings were taken, I placed them I a standard substrate, grain size 2-5mm pushing them in until half of the cutting was below ground.
Aftercare of hardwood cuttings
The cuttings sit outside in the shade all winter, receiving the weather that all the plants get. I will leave them there until spring is about to arrive. At that point I will move them to a warm spot, and cover the tray with some transparent foil to keep humidity up. Until then, the cuttings have time to start developing callus on the cut ends. I hope that come spring enough callus will have developed to push roots once the buds open.
Telling whether hardwood cuttings have roots
Stems do not need roots to open the buds. Instead, it rather is the presence of foliage that stimulates root formation. So if you do this, the opening of buds is a critical phase during which you must avoid the plant drying out, and keep humidity very high, to support the cutting in growing roots. Furthermore, once the plant starts to develop roots, these are very weak, and can break very easily. Therefor it is better to wait until you see strong top growth before doing anything to them. This includes pulling the cuttings to tell whether they have roots. Who has thought up that ‘trick’ has caused many freshly rooted cuttings to die due to root loss.
In general I tend to wait for leaf drop in fall to check on rooting. In some cases I am surprised that something which grew, does not have roots and plants that stuck to 2 leaves all year, have grown roots. Just be patient!