Staking tall flowers is always a challenge. I find using metal tomato cages or green metal hoops supporting the taller blooms works best for clumps or clusters of flowers. If you have zinnias planted in a row, you can place metal or bamboo stakes along the row of flowers on both sides of the border. Then use twine to connect the stakes and trap the flowers inside the webbing of string and stakes. Growing tall flowers against a wall also can keep tall flowers upright with less exposure to wind or rain. Keep Growing, Marianne Binetti