Phlox is a common garden plant that comes in many forms, with nearly 70 species of perennial and annual varieties, from creeping to tall, with flowers that bloom from mid spring through late summer. The three main types grown in gardens are creeping phlox, woodland phlox, and tall phlox. Colors range from white to shades of pink, purple, and blue. Most phlox will bloom in partial shade conditions. The taller varieties make excellent cut flowers and are attractive to pollinators. It is a favorite choice for cottage gardens.
I. Appearance and Characteristics
Phlox (; Ancient Greek: φλόξ “flame”; plural “phlox” or “phloxes”, Ancient Greek: φλόγες phlóges) is a genus of 68 species of perennial and annual plants in the family Polemoniaceae. They are found mostly in North America (one in Siberia) in diverse habitats from alpine tundra to open woodland and prairie.
The name is derived from the Ancient Greek word phlox meaning flame in reference to the intense flower colors of some varieties. Fertilized flowers typically produce one relatively large seed. The fruit is a longitudinally dehiscent capsule with three or more valves that sometimes separate explosively.
Some species such as P. paniculata (garden phlox) grow upright, while others such as P. subulata (moss phlox, moss pink, mountain phlox) grow short and matlike. Paniculata or tall phlox, is a native American wildflower that is native from New York to Iowa south to Georgia, Mississippi and Arkansas. It blooms from July to September.
Creeping phlox spreads rapidly and makes great ground cover. It can be planted to cover banks, fill spaces under tall trees, and spill and trail over slopes. Creeping phlox blooms in spring and produces long, spreading stems, which become woody with age. It was introduced into cultivation by the late 1700s.
The foliage of Phlox is a food for the larvae of some Lepidoptera species including dot moth, Gazoryctra wielgusi, hummingbird hawk-moth and Schinia indiana (which feeds exclusively on P. pilosa). Phlox species are also a popular food source for groundhogs, rabbits and deer.
Several species and cultivars of phlox are commonly grown in gardens. Most cultivated phlox, with the notable exception of Phlox drummondii, are perennial. Species from alpine habitats (and cultivars derived from them) require full sun and good drainage. Those from woodland habitats (such as Phlox divaricata) require partial shade and soil rich in humus. Those from waterside habitats (such as P. paniculata) require full sun and moisture at the roots. Phlox are valued in the garden for their ability to attract butterflies. Phlox can be propagated from stem cuttings.
II. How to Grow and Care
Sunlight
The light requirements for phlox differ, so you need to make sure you match the variety of phlox to the light conditions of your intended planting site or vice versa. Tall garden phlox needs full sun to thrive. On the other hand, woodland phlox should be in partial shade—light conditions that mimic its native habitat as an understory plant.
Temperature and Humidity
Tall phlox may wilt a bit on a hot summer day. Give them cool water at the base if the flowers or stems droop. Humidity can be an issue for phlox because of a tendency for powdery mildew to form on the leaves. This mildew is harmless to the plant but is somewhat unsightly, causing a pale gray bloom to appear on the leaves. The best way to prevent powdery mildew on phlox is to make sure the plants have adequate air circulation, so be sure they have space. If they start to get crowded they can be easily divided.
Fertilizing
Generally phlox don’t need any fertilizer, but if your soil is thin you should add some amendments. Tall and woodland phlox also benefit from a bit of top dressing with compost or composted manure in the fall.
Planting Instructions
You can plant phlox either in the spring after there is no more danger of frost or in the fall, at least one month before the first fall frost, to give the roots time to get established.
Dig a hole at least twice the size of the nursery container and deep enough so that the top of the root ball is level with the soil surface. Backfill the hole and gently tamp down the soil around the base. Water immediately.
Spacing depends on the type of phlox because the width or spread of the mature plant varies greatly. Plant tall garden phlox about 18 inches apart and leave about 2 feet between creeping phlox types.
Pruning
Phlox needs more cleanup than pruning to prevent the perpetuation of plant diseases such as powdery mildew. In the fall, after the first killing frost, cut the stems back to a height of 2 inches. In the spring, remove all dead foliage from the plants, making room for new growth.
Propagation
Phlox often reseeds itself freely. If you want the small volunteer plants elsewhere, dig them up and replant them in another spot. They will undergo a transplant shock, but if you keep them well-watered, they will recover after about a week.
Otherwise, you can also propagate phlox from stem cuttings. In the late spring, take a 4-inch cutting of a healthy stem and remove the lower leaves. Dip the cut end in rooting hormone powder and insert it about halfway in a 4-inch pot filled with damp potting mix. Place the pot in a location with bright light but away from direct sunlight, and keep it moist but not soggy. It will take at least a month for roots to develop. Wait until the cutting has grown a bunch of new leaves before transplanting it into garden soil.
Potting and Repotting
For container plants, choose a short variety, such as creeping phlox. Plant it in a container with large drainage holes and fill it with a well-draining potting mix. Potted phlox looks best when it fills the container, so plant more than one and leave at least 6 inches between plants. Keep in mind that unlike phlox planted in garden soil, potted phlox needs frequent watering and also repeated fertilization as the nutrients wash out.
When the roots have filled the pot or grow out of the drainage holes, repot the plant in a container that is 2 inches larger in diameter. Fill it up with fresh potting soil.
Overwintering
Being very cold hardy, phlox don’t need any special overwintering care. They do benefit from a top dressing of compost or manure in fall, and you may also put a light layer of natural mulch around them to protect the roots from extreme cold.
How to Get to Bloom
Phlox are prolific bloomers in the garden. But there may be various reasons why they don’t bloom as vigorously as they should. Be sure to give adequate sun exposure to the varieties that like sun (tall phlox and moss phlox especially, which need six hours of sunlight).
Powdery mildew can weaken the plant and this may affect the bloom output. Trim any mildewy leaves or cut those stems out to help keep the plant healthy. Dividing phlox plants that have become large or overgrown will also help to ensure healthy bud and flower production. You can divide plants in early spring or in the fall.
- Deadheading, Trimming and Pinching
Moss phlox can get a bit leggy which can affect the formation of flower buds; be sure to keep the plants trimmed. The best time to shear them is after the first flowering in spring; sometimes moss phlox will give a second gentle round of flowering in late summer. You can also deadhead the spent flowers to keep the plants neat and make room for more blooms.
Some gardeners swear by cutting tall phlox back by about a third in early summer, to encourage more branching and more flowers. You can also pinch back the pairs of leaves at the top (like you would with mums) through the first week of July to encourage fluffier panicles of flowers.
- Blooming Months
Woodland phlox start blooming in late April to early May and bloom for few weeks. Moss phlox start blooming usually in May. They have shorter bloom times than tall phlox, which usually start flowering in late June to July. To extend the summer bloom period, plant varieties of tall phlox that bloom across the season: some start flowering in late June, some not until August. The ‘Early Start’ cultivars begin blooming in early June. ‘Franz Schubert’ is a pretty pale lilac heirloom that blooms from late summer to early fall.
Pests and Diseases
Phlox have two main issues: hungry wildlife, and powdery mildew. Rabbits and deer love to nibble phlox. They like the flowers of woodland phlox, and then they’ll eat the young leaves of tall phlox, which can delay the buds from forming. Using a natural repellent spray made for deer or rabbits should deter them.
Powdery mildew on the leaves can be prevented by leaving room between plants so the phlox can get adequate air circulation. Watering at the base of the plant and not from overhead can also help prevent mildew.
Phlox may also be bothered by spider mites, especially in warm, unusually dry weather. The leaves may turn yellow and curl downward. These can be removed by spraying your hose on the undersides of leaves to dislodge the mites and their young.
III. Uses and Benefits
Phlox is one of those dependable summer flowers any large sunny flowerbed or border shouldn’t be without. There are several different kinds of phlox. Garden and meadow phlox produce large panicles of fragrant flowers in a wide assortment of colors. They also add height, heft, and charm to a border. Low-growing wild Sweet William, moss pinks, and creeping phlox are effective as ground covers to fill in spots under trees or next to structural walls where grass won’t grow or on slopes to add dimension and color.
Garden, meadow, and low-growing types all attract pollinators such as bees and hummingbirds, so if you plant phlox, you’ll have plenty of visitors. Butterflies are also fans of these blooms.
