DogThumbs, if half or a little less of a stem is still attached to the "mother plant" you may be able to reattach the broken part. You can either use florist tape (green, easily removed, and available at craft stores or at florists) to tape the broken parts together, or you can use small flat pieces of wood to make splints to hold the two pieces together by positioning the splints and wrapping twine around the splints. This is ideally a two-person process. A neighbor's cow came rampaging through our orchard area and broke the top of a young apple tree. I didn't have the florist tape so we used electrician's tape to put the main branch back together. This year that tree produced lovely apples. Gardeners live on hope!