I recently planted a Lemon-Lace Elderberry (a Sambucus racemosa cultivar). Since I've read online that elderberries produce much more fruit if planted in multiples of different varieties, I'm looking for a mate for it. I'm planting in a very small yard though, and other varieties of S. racemosa grow very large - the other elderberry varieties that are described as small are all varieties of S. canadensis. I've only got room for a small bush. My question is, will S. racemosa cross-pollinate with small S. canadensis cultivars like "Ranch" or "Nova"? Or do I really need another red elderberry?
I'm planting the elderberries more for the birds than for myself, if that matters. And I'm in USDA hardiness zone 6b.