This depends on the type of look you’re going for. However, nothing disrupts the look of a room more than a bunch of flowers sticking out awkwardly. As a general rule, flower stems should be no longer than 1.5 to 2 times the height of your vase. For example, if your vase is 30 cm long, you’ll want to leave your flower stems no longer than 45 cm - 60 cm.