It has been a windy autumn and winter here and when some S.elegans side shoots got snapped by falling debris I trimmed them and shoved them in a bottle of water which is outdoors in a sheltered spot - they are producing roots. I've treated some S.gesneriiflora side shoots the same and so far I have no roots although the cuttings remain healthy.
Generally though I agree with Robin - I usually strike cuttings in a light and airy soil based medium. Cleaning the pots thoroughly and microwaving the soil once the pot has been filled reduces the risk of rot as does light watering from the bottom only. cover the pot to raise humidity.
In my experience the thin stemmed shrubby species have a significantly lower strike rate than the thick square stemmed herbaceous species. I've found the best material for the shrubby species is semi-ripe growth and it is best to try in mid to late spring.
One other method that I have used on S.glutinosa (with 100% success) is layering. Peg the shoots down in early summer (whilst they are still flexible enough) and then the following year in late spring sever the shoot from the main plant. Carefully lift the new plant about six weeks later (if the weather is hot leave them until it cools down a bit) and grow on in a pot or transplant to the new spot in the garden.
