Any time from August to March. Use a tip cutting Apply 0.1 to 0.3 IBA (Rooting hormone) Stick in well drained soil & mist taking 40-80 days to root & 1.5 years to produce a 1 gal plant.

Anything will flourish in B.C.!!! I have had great success with rooting I. verticillata by taking cuttings in March, using Indole butanoic acid(0.3%, or Hormodin #3, and placing the rooting box upon a heating pad. The type of rooting medium seems not to be very important as long as it is well drained.
Substantial rooting was effected in about 8 weeks. The young plants were then potted in commercial ProMix, wetted with a dilute complete fertiliser solution,and kept in a warm, sunny site protected from the wind. These grew very rapidly throut the warm spring and summer and were ready to be placed in a permanent position the following March.

Thank-you both for the response to my email. I shall take some cuttings in March and see what happens.
Anyone know how close the male plant needs to be for effective fertilization?

as long as the wind pattern blows from one plant to another with the male up wind they can be 1000ft(+) apart otherwise on the same side of the building or 8-10 ft apart. One male can work for 8 female plants