Hummingbird feeding from red flower. If you're deadheading perennials in June, it pays to be selective. While removing spent blooms can encourage repeat flowering, some nectar-rich plants are far more valuable left intact, providing a vital food source for hummingbirds as they prepare for their long migration south later in summer. Take salvias, for example. A mature clump can produce dozens of flowering stems, each covered in nectar-rich tubular blooms.