Plant taxonomy designates woodland phlox, an herbaceous perennial, as Phlox divaricata. The plant belongs to the Polemoniaceae family, as does Jacob's ladder. Other common names for it include wild sweet William and wild blue phlox. Since this perennial grows wild, you may not be as familiar with it as you are with the commonly cultivated types of phlox, but they do belong to the same genus.
What Does This Perennial Look Like?
Woodland phlox flowers vary greatly in color. Some are light purple, violet or violet-blue, others a lighter blue; still, others are rosy lavender. Many people prefer the violet-blue color and find it in the cultivar 'Blue Moon.' But there are a number of other cultivars, including a white one: 'Fuller's White.' These plants have fragrant flowers, which bloom in clusters in April or May, depending on your region's climate. Leaves can be evergreen at the more southerly end of their range.
Individual plants grow to be about 1 foot tall or slightly greater, with a similar width. But this is a perennial that will spread (both vegetatively by rooting where leaf nodes touch the ground and by reseeding) under favorable conditions, eventually forming a colony. Indeed, the specific epithet, divaricata translates from the Latin as "spreading."
Growing Conditions for Woodland Phlox
Indigenous to the woodlands of eastern North America, where it grows in dappled shade with moderately moist soil, the suggested planting zones for woodland phlox are 3-8. Find a location in your landscaping that will best mimic its natural habitat, providing this perennial with dappled shade. For soil, it likes good drainage and will profit from ample humus. Make sure to supplement Mother Nature's rainfall, as needed (enough to keep the soil evenly moist).
Speaking of moisture, an application of landscape mulch will help you retain moisture in the location you have selected. A problem in growing woodland phlox that is less easy to solve is the potential attack of powdery mildew upon its leaves. As with any plant susceptible to mildew (or to fungus, in general), aeration (through spacing) can help. It can also help to give these perennials a haircut after they've finished blooming since rampant growth can be an invitation to powdery mildew.
To propagate, divide these perennials in spring.
Wildlife Attracted to Woodland Phlox Flowers
Uses in Landscaping
If you live in eastern North America and seek blue flowers for a dappled-shade native garden, then woodland phlox is an excellent choice. If you live elsewhere but find this perennial attractive, consider trying to naturalize it in your landscape. Given the right growing conditions (see above), it can be a splendid plant for woodland gardens anywhere.
More generally, treat it as a flowering ground cover or edging plant, especially where you need color specifically for spring. A potential drawback in using it as a ground cover is that it does not stay as short as do many of the more conventional ground covers.
Regarding the geographical range where this perennial is native (namely, eastern North America), it is curiously absent from most of New England (it is native only to Vermont and Connecticut in that region).
Other Kinds of Phlox
The various types of phloxes are popular landscape plants. Of the examples we list below, numbers one and two are best if you want a low ground cover, while the others―which are considered types of "garden phlox"―are taller: