Make the cut just below a node on a non-flowering stem.
Remove the lower leaves, dip the end of the cutting in rooting powder/gel (optional) then insert it vertically in pots/trays filled with moist seed/cutting compost.
Note; If the top pair of leaves are quite large it is sometimes an advantage to cut the leaf tip off.
This reduces transpiration thus preventing the cutting from drying out before rooting takes place.
Place the pot / tray in a warm place, preferably with bottom heat.
A soil temperature of around 16°C (60°F) and a minimum air temperature of 4°C (40°F) is ideal.
Give the cuttings plenty of light, but ensure that they are not scorched by direct sunlight.
Spray cuttings at least once per day with either fresh water or a fungicide mixture to prevent dehydration.
A sign that they have rooted is, the growing tip will be a ‘fresh’ green colour.
Pot on into 75 mm (3") pots of potting compost when rooted.