Using Zinnias in flower arrangements
When cutting zinnias for flower arrangements, pick the flowers in the morning when they're fully open. Unlike other cut flowers, zinnias will not continue to open once cut and brought indoors.
Bring a pail of water into the garden when cutting and drop the stems into the water immediately after cutting. Be careful not to crush the hollow zinnia stems, or water will not freely flow up the stem to support the flower and the flower will wilt earlier. Cut zinnias right above a set of leaves. This will stimulate new branches to form and potentially more flowers to grow.
Once indoors, strip all but the top leaves off the stem, recut the stems to the proper height for the vase. Try to recut the stem bottom at a 45 degree angle under water to prevent air bubbles from entering the stem and blocking the flow of water.
Use a floral preservative in the vase water and change the water every few days. When changing the water, recut the stem bottoms. Your zinnias should stay fresh for up to a week, especially if the air is cool. When arranging colors, look to complement pale-colored varieties of white, pale yellow and green with bright red, orange and golden colored flowers. While a vase of all zinnias is stunning, adding a few to a bouquet of other cut flowers is a good way to add pop to the arrangement.