Semi-hardwood cuttings are best rooted in the fall. See the following link.

Here is a link that might be useful: Useful link

I don't exactly follow the advice in that article. My method is to wait til after we have a frost or Thanksgiving weekend, whichever comes first. Then I snip off small branches on the side of the plant about a foot long with some of the woody type of bark (not the softer green stems). I stick them down into a one gallon pot with any sort of potting soil mixed half and half with sand and I only fill the bottom third of the pot. I stick the stem into the center and allow the walls of the pot to support the stem. The first set of roots are going to be very fragile and can easily break off if you move the pot. I like to root larger woody stems with lots of side branches so that they will support the plant in the pot - and, you end up with a larger plant in the Spring than you would if you root a small green cutting. This method works for Rosemary also. I don't spend a lot of time fussing over them and rarely water them. I set them out of the way in part shade and leave them alone until things warm up in March.