Place the potatoes in a saucepan and add 1 tablespoon salt and enough water to cover generously. Bring to a boil and cook for approximately 15 minutes, until the potatoes are tender but still firm in the center (use a fork to check whether the potatoes are done). Drain the potatoes and allow to cool slightly, then cut them in half and place them in a large bowl.
Meanwhile, cook the beans in lightly salted boiling water for 4 to 5 minutes, until just tender. Drain. Add the beans to the warm potatoes, then add the herbs, garlic, capers, and lemon zest. Combine the oil and lemon juice in a measuring cup, pour over the potato salad, and toss to mix well. Season with salt and pepper. Let stand for a few hours at room temperature so that the herbs will have time to flavor the potatoes. Sprinkle with edible flowers, if desired, just before serving.