In short
- Blooms abundantly and fragrantly from July to September.
- Needs fertile, moist soil in sun or partial shade.
- Prone to powdery mildew - good airflow and watering at the base are key.
- Strongly attracts butterflies and bees.
- Divide clumps every few years for health and abundant flowering.
Botanical data
- Family
- Polemoniaceae (Polemoniaceae)
- Height
- 0.6–1.2 m
- Width
- 0.4–0.6 m
- Habit
- Upright
- Growth rate
- Moderate
- Position
- Full sun, Partial shade
- Soil
- Humus-rich, Loamy
- pH reaction
- pH 6–7
- Moisture
- Moderate, Moist
- Bloom
- July–September
- Hardiness
- USDA 4a–8a
- Propagation
- By division, From cuttings
Characteristics
An upright perennial forming clumps of stiff stems with lance-shaped leaves, topped with large, dome-shaped panicles of small, fragrant, five-petaled flowers in shades of pink, white, red, and purple. The clump reaches 60-120 cm in height and 40-60 cm in width, and the stems - unbranched all the way up to the inflorescence - regrow each year from the base. The leaves are opposite, sessile or very short-stalked, 5-12 cm long and entire, with prominent lateral veins that join into a marginal vein running along the edge of the blade - the feature that distinguishes garden phlox from meadow phlox; the lower part of the stems goes bare with age, especially when the plant dries out or is affected by powdery mildew. The corolla is fused: a single flower has a narrow tube ending in five flat, spreading lobes, measures 2-2.5 cm across and often carries a contrasting "eye" at the base of the lobes; several dozen flowers are gathered into a dense, dome-shaped panicle 10-20 cm in diameter. The nectar sits at the bottom of the long corolla tube, so it is reached mainly by butterflies and hawk moths, while bees collect chiefly pollen from phlox. Growth is moderate and the clump stays vigorous for about a decade. It differs from related species in habit and in the shape of the inflorescence: meadow phlox (Phlox maculata) has an elongated, cylindrical panicle, narrower leaves and spotted stems, while moss phlox (Phlox subulata) is a low, creeping rock-garden perennial with needle-like leaves that flowers in spring. It needs sun or partial shade and fertile, humus-rich soil kept consistently moderately moist at pH 6.0-7.0; it tolerates drought poorly but frost well - in our climate it overwinters without protection, and the recommended hardiness range is zones 4a-8a.
Popular cultivars
- ‘David’
- White, one of the cultivars most resistant to powdery mildew, 90-120 cm tall and distinctly fragrant. In 2002 it was chosen Perennial Plant of the Year by the American Perennial Plant Association.
- ‘Blue Paradise’
- One of the bluest cultivars in trade: in the morning and evening the flowers shift towards violet with a navy cast, while in full midday sun they turn purple. About 80-100 cm, with dark stems.
- ‘Bright Eyes’
- Light pink with a distinct carmine eye, shorter than the type (60-90 cm), so it needs staking less often. A classic of cottage borders and of the front row of tall perennials.
- ‘Starfire’
- One of the darkest reds in the species, with carmine-scarlet flowers; the young shoots and leaves take on a brownish-red color. About 70-90 cm, a strong contrast for whites and silvers.
- ‘Nicky’
- Intensely purple-carmine, one of the darkest purples in trade, with very dark stems; 80-110 cm. In the trade it is sometimes offered as, and identified with, the cultivar Dusterlohe. It needs light-colored neighbours, otherwise it is lost in the depth of the border.
- ‘Norah Leigh’
- Grown mainly for its foliage - broadly margined in creamy white. The flowers are pale lilac with a pink eye, growth is weaker (70-90 cm), and it needs a more fertile site and shelter from harsh sun.
Growing and care
Watering
Requires consistent moisture — it wilts when dry and becomes more prone to powdery mildew. Water at the base, not on the leaves.
Fertilizing
Regular feeding supports abundant, long-lasting bloom.
Planting
Fertile, humus-rich, moist soil in sun or partial shade; ensure air circulation between plants to prevent powdery mildew.
Pruning
Remove spent flower heads to prolong flowering; cut stems back to the ground in fall. Thin out the weakest stems in the clump in spring for better airflow.
Companion plants
Good companions
Similar requirements — fertile, moist soil and sun; phlox fills out the rose bed and extends summer bloom.
In partial shade, phlox and hosta share a preference for moist, humus-rich soil, complementing each other in form.
Bad companions
Lavender needs dry, well-drained soil — the opposite of phlox's moist site requirements.
The evidence level indicates whether the relationship is backed by research, observation, or gardening tradition.
Diseases and pests
A white, powdery coating on leaves, shoots and buds. The leaves turn yellow, become deformed and drop prematurely. The coating develops on both sides of the leaf blade, is often clearly visible from above, and can easily be rubbed off with a finger — it is the superficial mycelium of an ectoparasite that draws nutrients from the epidermal cells by means of feeding structures (haustoria). At first single, round, white spots appear, which in time merge and cover the entire leaf surface and the young growth. Young leaves and the current season's shoots are the most susceptible; heavy infection causes them to pucker, stiffen and stop growing, and on buds it leads to deformation or death of the flowers. On the fruit of some species (gooseberry, apple, cucurbits) the coating leaves russeting or a corky skin. Towards the end of the season, small, dark fruiting bodies (chasmothecia, formerly called cleistothecia) — the pathogen's overwintering structures — appear within the coating. The disease affects many plants, including roses, oak, privet, lilac, cucurbits, cereals, grapevine, apple, gooseberry, phlox and coneflowers, with each of these hosts being infected by a specialised species of fungus.
Septoria leaf spotNumerous small, round spots appear on the leaves with a lighter, greyish centre and a darker, brown margin. Within the spots tiny black dots are visible – pycnidia, the fruiting bodies of the fungus, which distinguishes this disease from other leaf spots. The infection progresses from the lower, oldest leaves upwards; with heavy infection the spots merge, the leaves yellow, dry out and drop prematurely, weakening the plant. Affected plants include tomato, currant, phlox and many perennials. The spots are usually 2–5 mm across; the decisive identifying sign is the dark pycnidia at their centre – best seen through a hand lens, and in high humidity exuding whitish 'tendrils' of spores. Leaves densely peppered with spots look as if dusted. The disease is favoured by warm (about 20–25°C), humid weather and water lingering on the leaves for a long time (rain, dew, overhead watering). On tomato the infection is confined almost exclusively to the leaves and leaf stalks – the fruit usually stays healthy – but the loss of the photosynthetic apparatus leads to smaller fruit and exposes it to sunscald.
AphidsSmall (1–3 mm) soft-bodied insects, green, black or pink, feeding in clusters on young shoots and the underside of leaves. They excrete sticky honeydew. The diagnostic feature that distinguishes aphids from other small sucking insects is the pair of siphunculi (tubular projections) at the rear of the abdomen together with a tail-like cauda; a single colony usually holds wingless forms (parthenogenetic females) alongside winged migrants that fly onto new plants in summer. In summer aphids reproduce parthenogenetically and viviparously over many generations, so the population builds up explosively; in autumn many species produce a sexual generation that lays overwintering eggs on the host, and host-alternating species move between a winter host (often a tree or shrub) and a summer host (a herbaceous plant). Feeding symptoms include curling, crinkling and distortion of young leaves, stunted growth, yellowing, and the shedding of buds and fruitlets. Abundant honeydew coats the leaves, and the sooty mould fungus that develops on it forms a black film which limits photosynthesis; the honeydew is fed on by ants, which in return defend the colony against predators. Aphids are also important vectors of plant viruses (mosaics among them), transmitting them from plant to plant even during a brief probing puncture.
Toxicity
| For whom | Level | Notes |
|---|---|---|
| Humans | None | — |
| Dogs | None | — |
| Cats | None | — |
History and origin
Garden phlox arrived in Europe from eastern North America in the 18th century and became one of the most popular perennials in cottage gardens and perennial borders, now available in hundreds of cultivars. In the wild it grows in moist thickets, at woodland edges and in river valleys of the eastern and central United States. The species was described by Carl Linnaeus in "Species Plantarum" of 1753. Breeding flourished in the 19th century and the first half of the 20th - in Germany, Georg Arends and Karl Foerster were among those working on phlox, and some of the cultivars selected then are still in trade today. In Poland phlox, also known as plomyk, has for generations belonged to the canon of cottage gardens, planted alongside hollyhocks, delphiniums and peonies. Several dozen cultivars remain in regular sale - increasingly selected for resistance to powdery mildew.
Uses
For perennial borders, cottage and naturalistic gardens, and plantings for pollinators and butterflies. Also good as a cut flower. Because of its height of 60-120 cm it is planted towards the back of the border, in groups of 3-5 plants and 40-60 cm apart - more loosely than instinct suggests, because a crowded clump is the shortest route to powdery mildew. For the same reason, avoid places against a wall, next to a dense hedge, or in corners with no air movement. It combines well with purple coneflower (Echinacea purpurea), rudbeckia, tall ornamental grasses and dotted loosestrife (Lysimachia punctata), and in a rose bed it takes over the flowering in midsummer; bee balm (Monarda) is another good partner, though it shares the same susceptibility to mildew and needs an equally airy site. In partial shade, hostas and ferns are its natural companions. Lower perennials are planted in front of phlox to screen the bare lower part of the stems. For cutting, the panicles are harvested once some of the flowers have opened - the remaining buds open in the vase. Container growing is difficult: with its low drought tolerance the compost in a pot dries out too quickly, so typical tall cultivars are treated as garden plants, and only low-growing cultivars are suitable for containers, with daily moisture checks.
Trivia
- The name Phlox comes from the Greek word for flame, referring to the intense colors of the flowers.
- Phlox is a favorite of butterflies and hawk moths thanks to its sweet scent, which intensifies in the evening.
- The genus Phlox is almost exclusively North American - the only species whose natural range extends beyond that continent is Phlox sibirica, which reaches north-eastern Asia.
- Variegated phlox cultivars such as Norah Leigh can throw reverted shoots with ordinary green leaves; these grow more strongly than the variegated ones and gradually crowd out the cultivar, which is why they are cut out at the base.
Frequently asked questions
Why do phlox leaves get covered in white powder?
This is powdery mildew, to which phlox is especially prone. Good airflow (thinning the clump), watering at the base rather than on the leaves, and choosing resistant cultivars all help.
How can I extend phlox's flowering period?
Regularly remove spent flower heads - this encourages the plant to produce more side shoots with flowers and extends the blooming period.
How often should phlox be divided?
Every 3-4 years, in spring or fall. Division rejuvenates the clump, prevents overcrowding (which encourages mildew), and maintains abundant flowering.
Why has my phlox turned pale lilac?
The plant does not change color - these are self-sown seedlings. Seed from named cultivars produces seedlings that usually flower in a pale pinkish-purple; they grow more strongly than the cultivar and after a few seasons crowd it out of the clump. This is prevented by removing spent panicles before seed sets and by weeding out young seedlings around the plant. It is the same task that extends flowering - deadheading spent panicles also cuts off the route to self-seeding.
Does garden phlox need staking?
Cultivars up to about a metre in a sunny, airy spot usually stand on their own. The stems flop when the plant grows in too deep shade or receives an excess of nitrogen. Instead of stakes, the spring thinning of the clump described in this guide is more effective - fewer stems are stiffer and better lit. For the tallest cultivars there is one more option: shortening some of the stems by about one third at the turn of May and June, after which the clump is lower and flowers slightly later.
Sources
- Plants of the World Online (POWO)Database (GBIF, POWO…)
- RHS — Phlox paniculataInstitution / botanical garden
My note
A private note for this plant — saved in your browser.
