Single-flowered dahlias are striking. They may only reach a height of around a metre, and their flowers may only be about ten centimetres across, but single-flowered dahlias refuse to be overlooked. Part of this is due to their very dark, almost eggfruit-black foliage. I'd certainly grow single-flowered dahlias even if that were all they had going for them, but the dramatic foliage is only the beginning of their summer bounty.