This important genus of valuable garden plants includes reliable and colorful species that bloom both early and late, in sun and shade, and in a range of rich colors that is equaled by few other genera. Most Phlox grow best in full sun (or partial shade in the South) and moist, well-drained soil.
P. divaricata laphamii is at its best in partial shade and in well-drained soil enriched with organic matter. Plants prefer soil with a slightly acid to neutral pH. They have an informal habit and root where the stems touch the ground, allowing them to form a ground cover where conditions suit them. Cut flowering stems to the ground after the blooms fade to keep plants looking tidy.
P. paniculata and, to a lesser extent, P. carolina and P. maculata are susceptible to powdery mildew, especially in dry soil. Water deeply during dry spells to reduce the incidence of disease, and dust with sulfur (available at most garden centers) beginning in early summer. Thinning half of the shoots when 6″ tall in spring (to allow better air circulation) also helps keep mildew at bay and encourages plants to produce larger and longer-lasting flower heads.
Divide P. paniculata every few years, replanting sections from the edge of the clump and discarding the woody center.