Black tulips. Uh-oh, bulb flowers. "Colorful summer flowers such as gladiolas and Gerber daisies are less expensive this time of year. Chrysanthemums, snapdragons, carnations and alstroemeria are cheaper than in any other time during the year. July through August is the best time to buy any type of rose because of decreased demand. This is the time of year to buy orchids of all colors."