I have been experimenting with propagating black mulberry trees for some time. We have a beautiful 10 year old tree in our garden in Manchester that fruits well and has been doing for about 3 years now. Propagating black mulberries is an easy task in the more mediterranean climates but in the UK it’s proving to be quite difficult. I have not tried propagating them from seed as yet as it would take about 7 year before they bore fruit and I’m not that patient. I have instead been attempting to take hardwood cuttings. So far it would seem (contrary to what I have read) that the most success is to be had with cuttings taken in January on at least 2 year old wood.
All cuttings I treated with rooting hormone (powder or gel), though some, though which seem to have done the best have been left in water that is changed every other day for up to three weeks. The water I used was a homemade rooting solution made by cutting 2cm pieces of willow (any young willow whips will do) and covering them with water for 24 hours then straining the water and putting the cuttings into it. I make a large batch which I store and then use to change the water. Mulberrys when cut exude a milky sap, I think this inhibits root formation and can lead to the water going stagnant if it is not changed early on.
So far I have a several cuttings that have taken but a couple went into dormancy after being repotted and were showing few signs of growth for months. I recently took drastic action and cut them both back to their only remaining bud, and as luck would have it there buds began to swell within a day or two and they are now in leaf.