Last year I learned a new technique for propagating Lithodora diffusa. Most recommendations call for use of semi-hardwood cuttings to multiply this plant, but chance discovery taught me that root cuttings will produce vigorous plants more quickly than cuttings.
I have sheltered a 'mother plant' in our unheated polytunnel greenhouse, as insurance against our sometimes harsh winter cold. It has been a source for cutting material over the past few years. Last winter, it sent roots through the drainage holes of the pot, and into the sand floor of the greenhouse. Several robust leafy shoots were noticed where the root exited the pot, and before it vanished into the sand (ie: where the root surface was exposed to light and air)
After carefully lifting the potted plant, with it's new youngster attached, I cut the new plant away from its mother, and removed the parent from its pot. I decided to experiment with the unpotted plant, so I harvested several of the thicker roots, making sure these came from inside the pot (no shoots present).
The roots were potted up separately, with the cut surface set at, or slightly above the potting mix. No special care was given to these cuttings, they were kept evenly moist, and were set on the greenhouse floor. In short order, each root produced several shoots where the root was exposed to light and air. Plants derived from this method of propagation gained size far more quickly than my old method of using shoot cuttings and rooting powder. I did find that thicker roots were most likely to produce abundant growth. Although thinner roots also produced shoots, growth points were fewer in number and weaker in vigour.
