Phlox is a genus of 67 species of perennial and annual plants in the family Polemoniaceae. They are found mostly in North America in very diverse habitats, from alpine tundra to forest borders and open woodland, to prairies.
The wild varieties of perennial phlox have flowers in two-tone shades of mainly pink and white, as well as solid pink or pure white. All our beautiful garden hybrids are bred from these, and come in amazing hues of: purple, lavender, pink, salmon, scarlet, blue and clear white. Some cultivars even produce lovely bi-coloured flowers that have a brightly coloured centre "eye" with contrasting outer colour on the margins of the petals. The sweetly scented blooms are clustered in dense panicles and are rich in nectar, making them much-loved by bees, butterflies and birds. After pollination the flowers develop into dry seed capsules.
Perennial phlox is considered a classic option for flowering borders, and is also commonly known as “tall phlox” garden phlox”, “summer phlox”, and “border phlox. Unlike the annual phlox (Phlox drummondii), perennial phlox (Phlox paniculata), will come back year after year, providing flowers for many seasons.
The plants form upright clumps about 60 to 120cm tall with many branched stems clad with narrow, dark-green lanceolate leaves which occur opposite one another, that can spread up to 50cm or more. This herbaceous perennial will go dormant or semi-dormant in late autumn or early winter, and remain so until spring, when fresh growth appears.
The popularity of perennial phlox, and years of breeding, have resulted in shorter, more garden-worthy cultivars that flower in a variety of different colours, and dozens of cultivars have received the Royal Horticultural Award of Garden Merit (RHS) and remain extremely popular with hybridizers.
The 21st Century Series of Phlox is a good example of a modern and vastly improved variety that is vigorous, growing about 50 to 60cm tall with a spread of about 35cm, and for many months in summer and autumn it will produce its irresistible clusters of delicate blooms in shades of dark to light pink, purple and white.
Phlox paniculata Image by Maria from PixabayUses:
Like many other vivid and fragrant plants, Phlox paniculata has medicinal uses as well. Extracts from its leaves are reportedly used to treat boils, and as a laxative and treatment for stomach pains. The vegetative parts can be used to make tea for the treatment of indigestion.
In the Garden & Home:
Among the Phlox species, Phlox paniculata is the only one that is considered edible, and because the flowers taste slightly spicy and sweet, rather like that of sugar snap peas, they are often candied to decorate cakes and desserts, or used as a colourful garnish for fancy cocktails, salads, and summer soups. Needless to say, the flowers with their sturdy stems also look stunning in flower arrangements!
An added bonus is that perennial phlox is non-toxic and safe to plant in children’s gardens, and places frequented by pets and wildlife.
Unsurprisingly, drawn to the flowers by both their colours and fragrance, perennial phlox attracts all sorts of pollinators, including bees, butterflies and moths, and even nectar eating birds.
This summer favourite brings high-impact colours, especially when it receives full sun. It is a versatile species which fits effortlessly into modern garden styles, herb and vegetable gardens, or traditional cottage gardens. It can be cultivated as a tall ground cover or as a small bushy plant, making it perfect for flower beds or borders, rockeries, and mass plantings.
Perennial phlox combine well with many other herbaceous perennials, and for a more contemporary look, combine them with ornamental grasses.
Phlox paniculata Image by Monika Schröder from PixabayCultivation:
Perennial phlox grows best in temperate regions with good summer rainfall, and is hardy to cold and frost as it becomes dormant in cold winter regions, with fresh growth emerging again in spring.
In warmer winter regions, when daylight hours are shortened, it may also enter a period of dormancy, or become semi-dormant.
It is not suited to very hot and humid regions, where it is susceptible to fungal diseases like powdery mildew. However, newer varieties have been bred to be more resistant to fungal diseases, and you can mitigate problems of heat and humidity by adding mulch to keep the root zone cool. Perennial phlox it also not really suitable for hot and arid summer regions, and and in our winter rainfall regions it will need to be watered regularly.
To grow phlox successfully plant in full sun to very light shade, and in moderately fertile, loamy or sandy, soils which retain moisture but also drain well.
Although not extreme water guzzlers, they need to be watered regularly, as the plants have fine feeding roots at soil level. Keep the soil evenly moist, but do not overwater, and to help prevent diseases avoid overhead watering, or water early to give the foliage sufficient time to dry out before nightfall. The shallow, fine roots also need to be kept cool with a layer of mulch, which should be topped up regularly. Feed with a good general purpose fertiliser for flowering plants in spring.
Good air circulation is essential for healthy growth, and helps to prevent both pest infestations and fungal diseases, so give the plants plenty of space to spread and grow. To induce continuous branching and vegetative growth, the plant should be pruned regularly through the peak growth period. Thin out spent flowering stems regularly, cutting them as far down the stem as possible, and if there are any signs of pests or diseases, dispose of the cuttings in the rubbish bin and not the compost heap.
If your area experiences snowfall, or in regions which experience extended frosts and heavy snowfall, the entire shoot system should be cut back to just 2 to 5cm above the soil in winter, and the roots can be mulched to prevent freezing.
Weed regularly around your plants so that weeds do not sap its strength or rob it of the water it needs to get through the summer. Weeds also harbour many pests.
Phlox paniculata Picture courtesy Nu leaf NurseryPropagation:
Perennial phlox can be planted using its seeds, vegetative cuttings, or rooted divisions. Propagation using cuttings and divisions is the easiest method.
Tip cuttings should be at least 4cm long. To hasten root production, they can be treated with a rooting hormone and then placed in a setup that receives around 12 hours of light.
Once seedlings or cuttings are large enough to withstand outdoor elements or have developed their first branches, they can be transferred to their permanent outdoor positions. Make sure to space them correctly to leave room for their branches. Branching can be induced by “pinching” young plants. This is done by removing the growth just above a node with buds.
Propagation by division of the plants in early spring is simple. Dig the plants out of the ground and split the large clumps into smaller clumps using a sharp knife, before replanting.
Seeds must be cold stratified before they are planted by placing them into a bag mixed with lightly moistened sand, and placing them in a refrigerator for about 1 to 2 months. Sow into trays filled with seedling soil and cover with a thin layer of soil. Germination can take 1 to 3 weeks when temperatures range from 15 to 20˚C. You can also sow seeds directly into garden beds in spring, as soon as the ground can be worked, covering them with 2mm of soil. Once germination takes place the seedlings should grow quickly and mature at around 90 days.
Problems, Pests & Diseases:
If grown correctly perennial phlox are largely pest and disease-resistant. Even their biggest problem, a disease known as powdery mildew, is rarely fatal but it can spoil their looks a bit. Powdery mildew can be quite challenging, especially in humid areas, and although modern hybrids are bred to be more resilient to disease, powdery mildew can still be a problem if the plants are planted too densely or watered too enthusiastically from above.
Click here to read more about powdery mildew
Young seedlings may need protection from slugs and snails.
When conditions are too hot or too dry spider mites can also become a major pest problem for this species. If infestations are severe, the plant may have to be treated with an organic pesticide.
Click here to read more about spider mites
On a lighter note, spacing out individual plants to ensure good air circulation, and regularly pruning can greatly reduce the chances of pest infestations and diseases. This also affords the branches more sunlight, leading to a higher abundance of flower heads.
Warning:
Phlox is a non-toxic plant which is safe for people with children and pets. It is not toxic to farm animals or wildlife either.