Taking hydrangea cuttings is really easy and you can expect at least an 80% success rate – although some species are easier than others.
H. macrophylla, H. macrophylla ssp. serrata, H. paniculata, H. heteromalla, H. involucrata – All very easy. Just take a main growing stem, about 8cms, (not a side shoot) with 3 pairs of leaves. Trim off the two lower pairs of leaves, cut the stem immediately through the lower leaf node, dip the cut stem in rooting hormone powder and place in a good, damp potting compost. Keep humid by using a soda bottle. Keep the soda bottle in place for 4 or 5 weeks, by which time the cutting should be rooted. No need to water during this time as the soda bottle prevents any moisture loss. These cuttings can be taken from May to September – maybe even later if you can provide bottom heat (heating mats).
H. arborescens (including popular cultivars ‘Annabelle’ and ‘Grandiflora’) – In May or June take a runner (whilst still small), and pot up. No hormone powder necessary. Again, I find it helps to use the soda bottle. You should get 100% success rate.
H. petiolaris, H. integrifolia, H. seemannii, H. anomala ssp. petiolaris var. ovalifolia (climbing hydrangeas) – Very easy, just like taking a cutting of English Ivy. Find a piece with signs of aerial roots beginning to grow. Separate it from the parent plant and pot it up. No hormone powder necessary, no soda bottles necessary. If you direct growth along the ground it will self-layer, – then you can just chop it up and pot it up. You should get 100% success rate.
H. aspera, H. quercifolia – These are much more difficult and I only get a 20% success rate – or lower! The problem is that they do not appreciate being kept humid, so don’t use the soda bottle method. This creates the problem of keeping them slightly moist but avoiding them rotting. They are slow to establish roots. June and July are the best months.
For all the cuttings I take in May-August I do not use the greenhouse.
It is possible to take hardwood cuttings in the winter, but the success rate is so much lower.
~ ~ Know your plant names so that you can apply the correct propagation methods ~ ~