Need tall flowering plant for partly shaded spot in USDA zone 8
I am fond of a clump of echinacea that chose to live on the south edge of my garden. It hasn't expanded in years, it just springs up in the same place year after year, and reaches 5-6 feet high. But what can I plant immediately north of it? The annuals I've tried there just sulk in the shade of the echinacea, except for cosmos, and even the tallest cosmos are too short to be seen above the echinacea. So it has to be something that will flower even higher than the echincea, and it has to tolerate the shade from the echinacea, at least for its first 5 feet or so. Tall sunflowers get floppy and don't do well there, perhaps because it's only morning sun shaded by the house in the afternoon. I would appreciate your suggestions.