There are many varieties of phlox available to gardeners, from dwarf varieties that are stunning in borders and beds to tall varieties that grow to 3 feet or more and are used in background plantings. A perennial, phlox produces spikes of brightly colored flowers that rise from the green foliage. Phlox can bloom for six weeks or longer when properly cared for. Deadheading removes the spent blossoms and prevents the phlox from setting seed, which helps prolong flowering while also keeping the plants attractive.
Cut off spent flower clusters as soon as the flowers begin to wither with a pair of small shears. Cut 1/4 inch above the bud that is forming immediately beneath the spent flower cluster.
Cut off the entire flower spike once all the buds have bloomed and there are no new buds forming along the stem. Cut the spike off where it emerges from the plant.
Dispose of or compost the removed flower clusters and spikes after deadheading. Phlox is prone to powdery mildew, and the fungal spores can survive in the dead plant matter, where they can then infect the entire plant.