What is the best way to propagate this plant from cuttings? Softwood cuttings in summer or hardwood cuttings in autumn?
Hydrangea is usually propagated from cuttings in early spring. Plants should be brought into warm and well lit conditions in the second half of winter. Good light is very important for getting strong and healthy fresh shoots, that suit well for cuttings. One - two buds per cutting is enough for propagation, so you can get several cuttings from one shoot. Good potting medium is sfagnum mixed with sand You may use some rooting stimulant to improve the rooting process, but you may try without it as well. For rooting period, daytime temperature should be +20...+25 Celsius degrees, night temperature may be lower. To keep high humidity, it is best to cover pots with a transparent cover (glass, polycarbonate or PVC membrane). If your plant is planted into the ground, then you may bend a branch and cover part of it with soil. Then keep this soil moist, until the branch is rooted.
Thanks for your reply, Sulev. I didn't realize that Dichroa is now classified as a hydrangea until I looked it up on this forum just before I posted. So are your recommendations specifically for dichroa or for hydrangeas in general? I don't have the facilities to try to propagate indoors in late winter but have had fairly good success in the past propagating outdoors in early summer or early fall with roses, hydrangeas, deutzia, fuchsias, mock orange and Korean lilac. Given that late winter propagating is not an option for me, what would be a better choice between early summer and early fall to try propagating?
My suggestion is for hydrangeas in general. I have no experiences specifically with Dichroa febrifuga Here Dichroa Febrifuga - Horticulture it is recommended to propagate late summer with semi-hardwood cuttings.