Make new plants by taking softwood cuttings. Cuttings Through the Year, a booklet published by the Arboretum Foundation(available for sale at the Washington Park Arboretum gift shop) suggests which plants to propagate month by month and how to do it. A few September plants include:
Rock Rose, Salal, Lavender, Holly, Penstemon, evergreen azaleas, Sweet box, Salvia, California Lilac and many others.
For a tutorial on taking softwood cuttings go online to a Fine Gardening article complete with clear color photos: www.finegardening.com/propagate-your-shrubs-softwood-cuttings