Phlox paniculata, more commonly known as garden phlox, grows natively in the eastern United States along streams and in wooded areas where the soil is rich and moist. Gardeners value Phlox paniculata for its attractive, long-lasting blossoms, sweet fragrance and longevity in the garden. This perennial flower produces blooms in shades of white, pink, red, purple and even bicolour, depending on the variety, and reaches up to 4 feet in height. Hardy in U.S. Department of Agriculture Hardiness Zones 4 through 8, garden phlox thrives in most areas of the country and returns year after year if proper care is provided.
Plant Phlox paniculata during spring or summer in a location that receives full sunlight throughout the day. Apply a 2-inch layer of peat moss over the planting site and use a garden tiller to work it into the soil to a depth of at least 12 inches prior to planting. Space plants at least 18 inches apart.
Spread a 3-inch layer of mulch over the site during midsummer to insulate the soil. Begin the mulch at least 3 inches from the crown of the plants to increase air circulation. Replenish as often as necessary throughout the growing season to maintain a depth of 3 inches. Increase the depth of the mulch to 4 to 6 inches when the ground first freezes. This is particularly important for plants that were newly planted in the fall.
Water Phlox paniculata once every week during the spring, summer and fall months. Apply water directly to the soil to reduce the risk of fungal disease. Decrease the watering frequency to once every 14 days during winter, when the plants are growing less actively. In colder regions no watering is necessary in the depths of winter.
Feed plants twice each year, once during early spring and again in midsummer just before blooming begins. Use a balanced 10-10-10 fertiliser and apply at the rate described by the manufacturer for the best results.
Use garden shears to thin Phlox paniculata plants to the strongest four or five stems once they reach about 6 inches in height. Pinch back the growing tips of the remaining stems by 2 or 3 inches to encourage a long and robust blooming period.
Phlox paniculata does best in soil with pH ranging from mildly acidic to mildly alkaline, roughly 6.1 to 7.5. Amend soil accordingly if the pH fall outside this range. Grow Phlox paniculata in partial shade if full sun is not available, though blooming will be reduced. Use a light organic mulch such as pine straw. If you must water your phlox from above, do so during the early morning, so excess moisture left on the foliage will evaporate in the sun. If you have planted colourful cultivars, deadhead your phlox by removing clusters of faded flowers to prevent fertile seeds from falling to the ground. Blossoms of volunteers that grow from fallen seeds are likely to revert to pale magenta.