Phlox paniculata Graf ZeppelinIn a sunny border, North American perennial phlox (Phlox paniculata) are one of my most long-lasting summer blooms, flowering for several months. They grow to a height of around 75 - 100 cm and have clustered heads of simple rounded flowers in a variety of colours, including pinks, white, red, cerise, mauve and purple. The very basic mauve form is best avoided, as it tends to spread too quickly. One unusual cultivar is 'Blue Evening', which changes from purple to a bluish colour towards the end of the day. Some Phlox have a contrasting eye to the flower, which can be used to echo nearby plants. I grow the pictured Phlox paniculata 'Graf Zeppelin' near to a hot pink Dianthus: an effective combination. I also find that the Phlox mingle well with my Dahlia and Salvia plants that grow nearby.
Phlox paniculata Blue EveningIf they are deadheaded through summer, new flowers will form. They should be staked with cradle stakes, as heavy rain can flatten them when they are in bloom. I cut them back to the ground in winter and divide the clumps up every three years, replanting into soil amended with compost and fertiliser. Mulch with compost to conserve moisture in the soil around the plants. Though they are best in sun, they can cope with a little shade, as long as they have fertile, moist but well-drained soil. Where soil is too dry, Phlox paniculata may develop powdery mildew. Make sure the plants have plenty of space as air circulation is also important to avoid the disease. Moisture on leaves at night can also encourage mildew so avoid watering them in the evenings.
The plants are fully hardy down to -30 degrees C, so can be grown in inland areas. The flowers are useful in vases: cut them early in the day.