Harvest cuttings from semi-ripe growth
The trickiest part of propagating shrubs from softwood cuttings is knowing when a shrub's stems are ready to be cut. Softwood, the section of a shrub's stem that's neither brand new nor fully mature, is the stage of growth on a deciduous woody plant that is best suited for rooting (for details, see Softwood is neither green nor woody, below). The newer, green growth that lies at the end of the stem will rot before roots are produced, and the older, more woody growth at the base of the stem has a harder time putting out roots.
Softwood cuttings can be taken from most deciduous shrubs in June and July and sometimes into early August. I determine a stem's maturity by taking it in my hand and bending it. If the stem breaks with a characteristic snapping sound, it is in the softwood stage and ready to be harvested as a cutting. If the stem is still too green, it will bend but not break. If the stem is entering the woody stage, it won't bend at all.