I found this info....If you are starting from scratch, you’ll have to decide what to plant with elderberry. White pine trees or quaking aspen are good elderberry companion plants, if you want something taller than the shrubs. For a plant about the same size, consider winterberry. Remember that elderberries do not like their roots disturbed once they are established. Therefore, it’s a good idea to install elderberry companion plants at the same time you plant the shrubs.
Other good ideas for elderberry companion planting include edging your vegetable garden with the shrubs or mixing them with other berry shrubs, like currants and gooseberries. Phlox and bee balm work well when you are planting with elderberries in this way.
Read more at Gardening Know How: Elderberry Plant Companions – Tips On Planting With Elderberries