What do flowers eat?

Flowers don't "eat" -- they absorb nutrients from the soil through their roots. These nutrients are primarily minerals such as nitrogen, potassium, phosopherus and others. Plants also make their own energy in the form of sugars. Utilizing light energy, carbon dioxide and water, via the process of photosynthesis, produce oxygen and sugar. The sugar is stored in the roots/bulb until needed by the plant for growth, flowering or seed/fruit production.