DOMES OF COLOUR
With its clusters of petals, sweet perfume and eye-catching hues, phlox elevates summer borders
IN THE HEIGHT of summer, when picnics are the order of the day, and the air buzzes with the sound of bees and lawnmowers, herbaceous phlox fill the air with their sweet fragrance. Sturdy clumps of upright stems hold the dense heads of delicate flowers aloft above lowly bedding plants and among flashy dahlias and delphiniums. Quintessentially a part of the English summer garden, the vast range of colours make phlox versatile as well as beautiful, and newer dwarf varieties are bringing them from the middle of traditional borders to the fore of modern gardens.
Phlox are hardy plants, with stems that rarely branch, except at the top at flowering times. They provide a vertical accent in the border, with pairs of narrow, pointed leaves set approximately at right angles up the stem. The stems and leaves are green in white-flowered varieties, but frequently purple-tinged, along with the young foliage. As flowering time approaches, the stems branch to produce pyramidal or domed heads of blooms.
Mounds of colour
The flowers have five petals to form a round, flat bloom, with a narrow tube behind.
Most varieties are fragrant, with a delicate, sweet, often slightly peppery scent, but it is the distinctive mounds of colour that make them so popular. The range of colours will satisfy the most discerning gardener, spanning pastel shades and bold colours. The boldest are those with contrasting eye colour, which can look busy in the border, while the many lavender and white varieties are ideal for a cool evening garden, with silver and grey foliage.
Border phlox are chunky plants, with stiffly upright stems, horizontally held leaves and domed or elongated heads of flowers. Most will reach 3-4ft (90-120cm) when in bloom, with a spread of approximately 18in (45cm) over two years. Newer varieties of phlox tend to be shorter, but will still achieve 2ft (60cm) or more in flower.
Young, vigorous plants will be taller than congested, old clumps, and all can be kept shorter by pinching out all the growing tips in mid May. This will slightly delay flowering as well as making the plants more compact, and can extend the flowering period of any variety.
Individual blooms vary from just under ½in (1cm) to just under 1½in (3cm) across. Generally, the small-flowered kinds have more blooms per flower head, and the heads are domed and up to 6in (15cm) across. Each head provides a succession of flowers for several weeks; the old blooms withering and dropping, allowing new buds to unfurl.
Phlox start to bloom in July and continue into August. If old flower heads are removed, the main stems produce short new stems and a second flush of small heads, continuing the display into September. The flowers attract a wide range of pollinating insects.
Phlox is a large genus, with more than 60 species. The name is derived from the Greek for flame and refers to the bright colours of the flowers. The genus includes herbaceous perennials, annuals and low alpines and woodland plants. Most are North American in origin, and the two most popular perennial species, P. maculata and P. paniculata, native to the east of North America, were introduced to the UK before 1740. They were hybridised in 1910 to produce the group of hybrids known as P. x arendsii.
Phlox maculata is a shorter, more slender and elegant plant than Phlox paniculata. Its flowers are also smaller and held in narrow, cylindrical clusters, unlike the mounded heads of P. paniculata.
The most important period in the development of herbaceous phlox was at the start of the last century, when selections of P. paniculata were made in France. Once the Arendsii hybrids were produced, work was continued by Karl Foerster in Germany and British phlox enthusiast B H B Symons-Jeune. Hundreds of varieties were introduced, and by the 1940s, there were more than 800 listed. But the fashion for herbaceous borders declined and the interest in phlox along with it, and by the 1980s, they were rarely offered for sale.
Meanwhile, Alan Bloom at Bressingham, Norfolk, was promoting herbaceous plants and, using the 80 varieties he had accumulated, started breeding new plants in the 1960s in the hope of producing pale pinks, which he noticed were absent among the popular varieties. The result was ‘Mother of Pearl’, its delicate pink and white ensuring that it remains popular to this day. He also worked with P. maculata and introduced both ‘Alpha’ and ‘Omega’, which remain the most popular varieties of all.
Growing conditions
Phlox are hardy plants, but are best planted in spring so they can have all summer to grow and establish. Small specimens planted in autumn may not survive winter, especially in poorly drained soils. The crown should be sited at ground level, and young plants or divisions can be spaced approximately 18in (45cm) apart, depending on how quickly the clumps are intended to intermingle and cover the soil. A single clump will make a good show and, planted in spring, will bloom the same summer. If grown in sun, the plants usually do not need to be staked, but the taller kinds may need support in exposed gardens.
Phlox grows best in a well-dug soil that is rich in organic matter. Clay soils, improved by cultivation, are better than dry, sandy soils that may lead to mildew in dry summers. Although often planted in prairie-style combinations, herbaceous phlox are not naturally prairie plants and in the wild occur at the edge of shrubby areas and near streams. They will grow in sun or shade, but will flower best and be more compact in a place where they get sun for most of the day. They are not too fussy about soil pH, but will do
best when planted in neutral or slightly alkaline soil. In acid conditions, the pH can be increased by adding fish, blood and bone around the plants in spring.
Phlox does not need to be divided every year, simply cut down in autumn, but these plants are prone to becoming woody at the base, so they are best lifted and divided after three or four years to maintain vigour. A mulch of compost and a sprinkle of general fertiliser should be applied in spring.
Because phlox bloom from midsummer onwards, the lower part of the plants can be scruffy by the time the flowers at the top open, so they are not ideal for growing in containers, and with the exception of the variegated kinds, the plants can look rather dull before blooming. It is possible, using a loam-based compost and large containers, but plants in pots need constant watering and feeding, and any hint of drought will encourage powdery mildew. To maintain vigour, container-grown phlox will need dividing and replanting every year or two.
Propagation
Although phlox can be grown from seed, unless hundreds of plants are required, it is better to buy named varieties that have been selected for their colour, habit and vigour than risk raising inferior plants.
Phlox can be propagated by dividing them in autumn or spring. To do this, established clumps are dug up and some soil removed to expose the roots. The clump is then cut into sections, each with at least three or four shoots, from around the edge of the clump. These should be replanted as soon as possible; watering them well to settle them in the soil.
An alternative is to take root cuttings, which should be done from autumn to spring. The dormant plants are dug up, with the soil carefully shaken from the roots, and then the thickest roots, ideally 5mm in diameter, are cut into sections 2-3in (5-7cm) long. These are placed in pots of gritty compost, the right way up, covering the upper cut surface with compost or grit approximately 5mm deep. Keeping the compost moist will see shoots appearing in spring. The young plants can be carefully potted later in summer or autumn.
Planting partners
Due to their wide range of colours, phlox can be combined with a huge variety of plants. Since they flower later than the early flush of border plants, they are useful to plant in front of early-flowering peonies, poppies and irises. Many of the colours combine well with fiery crocosmias and kniphofias, and offer a contrast of form. Early-flowering asters, such as A. amellus and A. x frikartii, start to bloom as the phlox are at their peak, and are useful to cover the base of the phlox.
Phlox also works well in prairie-style plantings with grasses, veronicastrum, echinaceas and rudbeckias, especially the smaller-flowered P. maculata types.
Phlox are among the brightest and boldest of summer border plants, hardy and easy to please. Their heads of flowers will bring colour to the garden for many weeks in summer, along with wafts of sweet perfume.
“here she paused in her gracious talk To point me a moth on the milk-white phlox”
Robert Browning, ‘Garden Francies’