book says,plant cuttings in a cold frame in summer.if you have the main plant
then look around it at the bottom and it will have set its own little plants.
if not then take small tip cuttings about 4inch and pop them in a pot and water in, then wait for the roots to take and pot them on when bigger.
they are very hardy and dont need special treatment.

Just a point - tip cuttings need to be from this year's growth. I'm sure if you check you will find self rooted cuttings (aka Irish mans cuttings!)