In short
- Flowers in April and May for 3-5 weeks, hiding almost the whole mat under bloom.
- The leaves are awl-shaped and evergreen - the plant covers the ground all year round.
- Requires full sun and free-draining, rather dry and poor soil; it will not tolerate standing water.
- Reaches only 10-15 cm in height, but spreads to 40-60 cm across.
- After flowering, shear the mat back by about a third - without this the centre of the clump goes bare.
Botanical data
- Family
- Polemoniaceae (Polemoniaceae)
- Height
- 0.1–0.15 m
- Width
- 0.4–0.6 m
- Habit
- Creeping
- Growth rate
- Moderate
- Position
- Full sun
- Soil
- Sandy, Loamy
- pH reaction
- pH 6–7.5
- Moisture
- Dry, Moderate
- Bloom
- April–May
- Hardiness
- USDA 3a–9a
- Propagation
- By division, From cuttings, By layering
Characteristics
A low perennial of prostrate habit: the stems spread radially over the ground, root at the nodes and form a dense, cushion-like mat 10-15 cm tall and 40-60 cm wide, and old clumps that are never rejuvenated can be wider still. The leaves are awl-shaped - narrow, stiff and pointed, 1-2 cm long - and grow in opposite pairs in dense, apparently whorled clusters; they are the source of both the Polish name of the species and the Latin epithet (subula = awl). The foliage is evergreen: the mat stays green throughout the winter, although in frosty, snowless spells it turns brown and partly dries out, rebuilding itself in spring. The flowers are 1.5-2 cm across and have five corolla lobes distinctly notched at the tip - the feature that separates the species from the very similar Douglas' phlox (Phlox douglasii), whose lobes are entire or barely notched. The colour ranges from white through pink and carmine to lilac purple, usually with a darker eye at the base of the lobes; the flowers are borne singly or in small groups on short stalks, and at peak bloom they cover the mat almost completely. Flowering falls in April and May and lasts 3-5 weeks, depending on how the spring runs. The nectar sits at the bottom of a narrow corolla tube, so it is reached above all by butterflies and hawkmoths and by long-tongued bees and flies; for the honey bee it is in practice out of reach, which is why, despite the abundant bloom, the species remains of little value as a nectar source. The flowers are only faintly scented - the fragrance can be caught close to on a warm day, but unlike garden phlox (Phlox paniculata) it is not one of this species' assets. The root system is shallow, so on a thin layer of substrate the plant feels drought quickly, yet drought itself it tolerates very well and it does not compete with deeper-rooting neighbours. It needs full sun and free-draining, rather poor, sandy-loam soil; it tolerates a reaction from slightly acid to slightly alkaline (pH 6.0-7.5) and grows best in neutral conditions. Hardiness is very high (zones 3a-9a), yet in our climate mats are lost more often to winter wet and standing water than to frost itself. From Phlox stolonifera - a woodland species that confusingly shares the name creeping phlox - it differs in habitat and structure: that one grows in shaded, moist positions, spreads by stolons and has broader, ovate leaves.
Popular cultivars
- ‘Emerald Cushion Blue’
- Lilac-blue, with a very dense, low-spreading cushion and abundant flowering; one of the most widely sold cultivars in this colour. In the trade it is often confused with the similar, also blue-lilac Emerald Blue.
- ‘White Delight’
- Pure white, with relatively large flowers; the best contrast for carmine and purple cultivars, and on a wall it brightens shaded corners.
- ‘Candy Stripes’
- White with a distinct pink stripe running down the middle of each corolla lobe, so that close to it looks two-toned and from a distance pale pink. It is also sold under the Japanese cultivar name Tamaongalei.
- ‘McDaniel’s Cushion’
- Intensely pink, with flowers larger than in the typical form of the species and a very dense, even cushion. It is sometimes offered under the shortened spelling Daniel's Cushion.
- ‘Purple Beauty’
- Purple-lilac with a darker eye at the base of the lobes, evenly smothered in flowers; it looks good next to white cultivars and grey-leaved rock-garden neighbours.
- ‘Scarlet Flame’
- The most saturated of the colours widely available in this species - carmine red, legible from a long way off, which is why it is readily planted on the tops of walls and on banks.
Growing and care
Watering
In the ground it really only needs watering in the first season after planting and during a prolonged drought. Excess water is more dangerous than drought - on heavy, wet soil the mat rots, most often in winter and early spring. In bowls and troughs the compost dries out much faster and needs checking.
Fertilizing
A thin layer of well-rotted compost spread around the mat is enough. Use nitrogen fertilisers with great care - an excess of nitrogen pushes out leafy growth at the expense of flowers and worsens overwintering.
Planting
A free-draining and rather poor substrate: mix heavy soil with gravel, grit or coarse sand, and on flat ground raise a slight mound so that water does not stand under the mat. Do not enrich it heavily with compost - on fertile soil the plant grows lush at the expense of flowering and overwinters less well.
Pruning
Cut the whole mat back by roughly a third, running the shears flat over the cushion. The cut removes the spent flowers, thickens the mat and encourages the stems to root at the nodes, so that the centre of the clump does not go bare. Dried-out and damaged parts are cut out separately, back to healthy growth.
Companion plants
Good companions
Kwitnie dokładnie w tym samym terminie (kwiecień–maj) i ma identyczne wymagania — pełne słońce oraz przepuszczalną, suchą glebę; obie rośliny tworzą płaskie poduchy, więc na koronie murku dają zwartą, dwubarwną plamę.
Ma te same wymagania siedliskowe, a kwitnie od czerwca do września — przejmuje kwitnienie dokładnie wtedy, gdy floks szydlasty przekwita i zostaje samą darnią.
Sucholubna trawa o kontrastowej, siwej i kępowej formie, wymagająca tego samego stanowiska; przełamuje monotonię płaskiej darni, nie zacieniając jej.
Bad companions
Wymaga półcienia i stale wilgotnej, próchnicznej gleby — dokładnego przeciwieństwa suchego, słonecznego stanowiska floksa szydlastego; dodatkowo jej szerokie liście zacieniają niską darń.
Rozrasta się długimi, ukorzeniającymi się pędami i w kilka sezonów przerasta niską poduchę floksa; woli przy tym stanowisko cienistsze i wilgotniejsze.
The evidence level indicates whether the relationship is backed by research, observation, or gardening tradition.
Diseases and pests
The disease develops in overly wet, poorly aerated substrate and attacks the roots and the base of the stem. The roots turn brown, rot and lose their bark, which slips off easily, and a dark, watery rot appears at the stem base. The above-ground part wilts, yellows and dies back despite moist soil – a characteristic symptom, because the damaged roots no longer take up water. Especially at risk are houseplants, succulents and cacti (from overwatering), and in the ground conifers, rhododendrons, ericaceous plants and strawberries on waterlogged sites. The process begins inconspicuously at the root hairs and root tips, which darken and disappear, after which the rot advances towards the framework roots and the root collar. Healthy, pale, active roots waste away — what remains is a dark, rusty-brown or blackish, watery mass, and the outer layer of the root bark slips off like a glove, exposing the discoloured central cylinder. In trees and shrubs, infection of the collar and the base of the trunk (stem-base rot) shows as a dark, often streaking patch, sometimes with oozing, and the bark there is moist and sunken; in conifers and rhododendrons, browning and dieback are seen from the bottom or from the centre of the crown while the soil is still moist. Characteristic is the nested (patchy) occurrence of symptoms in the bed — where water and the pathogen accumulate locally. It is worth distinguishing the two causal oomycete genera: Pythium mainly attacks seedlings and fine roots, causing damping-off and root rot in cool, wet substrate, whereas Phytophthora also attacks older, woody plants, framework roots and the collar, more strongly in warmer, water-saturated soil. Key for diagnosis is the contradiction of the symptoms: the plant wilts and looks 'dry', although the substrate is wet — this results from the destruction of the roots, not from a shortage of water.
Powdery mildewA 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.
Spider mitesTiny (0.3–0.5 mm) arachnids, hard to spot with the naked eye, feeding on the underside of leaves. Symptoms: fine, pale speckling (feeding punctures); over time the leaves turn grey, yellow and dry out. Under heavy infestation a fine webbing becomes visible. Warm, dry air favours their development — a common problem for houseplants in winter near radiators. Spider mites are not insects but mites of the family Tetranychidae — adults have 8 legs (larvae only 6). The most common in cultivation is the two-spotted spider mite (Tetranychus urticae): yellowish-green females carry two dark spots on the sides of the body, while overwintering females turn orange-red. In orchards the fruit tree red spider mite (Panonychus ulmi) is frequent, whose red eggs overwinter in clusters on the bark of the shoots. Feeding mechanism: the mites puncture the cells of the epidermis and mesophyll on the underside of the leaf and suck out their contents, and the emptied cells fill with air — hence the characteristic, silvery-grey, fine speckling visible from the upper side of the blade (resembling a mosaic discolouration). At high numbers the leaves turn brown, curl and drop prematurely, and the whole plant weakens and loses its growth. Dense webbing spun between the leaves and shoot tips appears only under an advanced attack and is a sign of the risk of the pest spreading to neighbouring plants. The development cycle is very fast in warmth and drought — at a temperature of 25–30°C a single generation can be completed in 1–2 weeks, hence the numerous generations per season and the rapid, exponential build-up of the population. Females lay spherical, transparent eggs on the underside of the leaves. Fertilised females overwinter (in bark crevices, leaf litter and plant debris) or — in the fruit tree red spider mite — the eggs on the bark. Early infestation is easy to miss; diagnosis is helped by shaking a leaf over a white sheet of paper (moving specks become visible) or examining the underside of the leaf with a magnifying glass.
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
The species comes from the eastern and central parts of North America, where it colonises sandy and rocky slopes, dry clearings and banks - from the states of New York and Michigan to North Carolina and Tennessee. It was described by Carl Linnaeus in Species Plantarum of 1753; the epithet subulata refers to the awl-shaped leaves. It reached European gardens in the 18th century and gained popularity along with the fashion for rock gardens, in which it became one of the staple plants - alongside aubrieta, candytuft and rock alyssum. Breeding went mainly in the direction of flower colour and the compactness of the mat, so that several dozen cultivars remain in trade, from pure white to carmine and lilac purple, including forms with striped flowers. In Poland it is today among the most frequently planted ground-cover perennials for dry walls, banks and edgings, and its spring flowering coincides with that of species tulips and grape hyacinths. The species made a separate career in Japan, where under the name shibazakura it is used to plant up parks covering many hectares.
Uses
A staple plant of rock gardens, the tops of dry stone walls and retaining walls, banks, bed edgings and gaps between paving slabs. It gives the greatest effect planted at an edge from which the mat can spill freely downwards - the hanging stems cover the stone and, in flower, turn it into a single sheet of colour. Plant about 8-11 per square metre at 30-35 cm spacing; the gaps between plants usually close in the second season. In paving joints it does well, but it will not take regular treading - it is no substitute for a lawn. It is also suitable for bowls, troughs and boxes on a terrace, provided the compost is free-draining and the container has a drainage hole. Do not mulch with bark or a thick layer of any moisture-holding material at the base of the mat; the right mulch here is grit or gravel, which draws water away from the root collar and additionally keeps the flowers clean after rain. It combines well with aubrieta, evergreen candytuft, rock alyssum, stonecrops, houseleeks and blue fescue, and low bulbs - species tulips, grape hyacinths and crocuses - look attractive pushing up through the mat. Once the phlox is over, thyme takes over the baton, so the rock garden goes on flowering through the summer. Do not plant it at the foot of vigorously spreading perennials and shrubs, nor in places shaded at midday: in shade the mat becomes drawn out, thin and flowers poorly.
Trivia
- The specific epithet subulata comes from the Latin subula, meaning awl - it describes the narrow, stiff, pointed leaves, from which the Polish name of the plant also derives.
- The genus name Phlox means flame in Greek and refers to the intense colours of the flowers; in moss phlox this is seen best in the carmine cultivars.
- The trailing stems root wherever they touch the ground, so the plant propagates itself by natural layering - it is enough to cut off a rooted piece of the mat and move it to a new place.
- In Japan the species is called shibazakura, or "grass cherry" - its small, five-lobed flowers resemble cherry blossom, and the plants hug the ground like a lawn. The largest plantings, such as the one in Hitsujiyama Park in Chichibu, run to hundreds of thousands of plants and draw crowds of visitors in spring.
Frequently asked questions
Why does moss phlox go bare in the middle of the mat?
This is the normal ageing of the cushion: new growth is produced around the edge, while the oldest part in the centre becomes woody and dies off. It is prevented by shearing every year immediately after flowering (cutting the mat back by about a third) and by top-dressing the plants with a thin layer of free-draining soil mixed with sand, which encourages the stems to root. A clump whose centre has already gone is best rejuvenated every 3-4 years by division, or replaced with a new plant raised from a stem cutting.
When should moss phlox be pruned?
Immediately after flowering, at the turn of May and June - in a single pass of the shears held flat over the cushion, cutting it back by roughly a third. It is not cut in autumn or winter, because the evergreen leaves protect the root collar, and cutting after July removes the growth on which next spring's flowers will be set.
Why does moss phlox flower poorly?
The commonest causes are too little light (in partial shade the mat thins out and flowers sparsely), soil that is too fertile or an excess of nitrogen fertiliser, which pushes out leafy growth at the expense of flowers, and the lack of an annual cut after flowering. Check as well whether the plants have been overgrown by their neighbours - moss phlox is too low to win the competition for light.
Does moss phlox lose its leaves for the winter?
No - it is evergreen and works as ground cover all year round. In frosty, snowless winters the mat may turn brown and partly dry out, but in spring it rebuilds itself from the living stems. Far more dangerous than frost is winter wet: on heavy, wet soil the plant rots, which is why free-draining ground is essential.
Is moss phlox suitable for planting between paving slabs?
Yes - the joints between slabs are a good place for it, because the substrate there is free-draining and warms up quickly. It will not take regular treading, however, so it is planted along the edges of paths and on surfaces that are walked on only occasionally. For places in real use, thyme is the better choice.
Sources
- Plants of the World Online (POWO)Database (GBIF, POWO…)
- RHS — Phlox subulataInstitution / botanical garden
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