Phlox are an old favourite having been grown in British gardens for more than 250 years. Mainly native to North America, there are around 68 different species. There are a wide range of types found growing in full sun, woodland and alpine tundra locations. They have flowering times ranging from spring to autumn.
The leaves of this plant are one of the main food sources for the larvae of the hummingbird hawk moths. And, in North America, tea made from dried leaves was used to purify blood. As well as helping to treat indigestion.
Folklore suggests that planting phlox in the garden encouraged family harmony. Victorian Americans often included the flowers in wedding decorations as the flowers were considered to signify united souls.
Plant Biography
BOTANICAL NAME
Phlox paniculata, placed in the famile polemoniaceae.
The name ‘phlox’ comes from the Greek word of the same name, meaning ‘flame’.
COMMON NAME
Phlox has many common names, perennial phlox, autumn phlox, cross-leaved phlox, summer perennial phlox, summer phlox, fall phlox and tall garden phlox.
NATIVE TO
Phlox is predominately a native of eastern USA with a handful native to Asia.
DESCRIPTION
There is great variety in the look of phlox. From low-growing (7cm-15cm), mound forming, covered in spring flowers. To spreading and/or upright (150cm) forms producing numerous star-shaped flowers.
What type of plant is it?
There are deciduous, evergreen and semi-evergreen species of perennial phlox as well as annuals.
What colours does Phlox come in?
There is a wide variety of flower colours, pink, purple, red, white and blue.
When do these plants flower?
There are many different flowering times for this plant, including spring, summer and autumn.
Where to grow Phlox
The growing conditions are varied, ranging from full sun, part sun and dappled shade.
Where not to grow Phlox
Avoid growing phlox in deep shade. They also dislike shallow soil that regularly dries out. For this reason, it’s more difficult to grow perennial phlox in containers unless the soil can be kept reliably moist.
Is this plant drought-tolerant?
These plants are not particularly drought tolerant.
How to grow Phlox successfully
Phlox grows well in full sun or light shade in nutrient-rich soil that stays reliably moist. As they are shallow-rooted mulching plants in the autumn helps moisture retention during the summer months.
Avoid overcrowding in borders as this can affect successful flowering. Keep emerging shoots clear of foliage from other plants in the border. Cut some of the flowered stems on the plant down to about 20cm after flowering. This can prolong the flowering of the plant.
Do they require supports?
There is not normally a need to support them unless grown in a very windy site.
Is it good for pollinators?
Is it good for wildlife?
The flowers are generally nectar and pollen-rich. As a result, attract many different types of pollinating insects, particularly bees, butterflies and moths.
How to choose the right variety for your garden
Check plant labels carefully due to the varied growing conditions of different varieties.
Annual varieties are excellent for growing in containers and/or as summer bedding plants. Phlox divaricata is best suited to part shade. And, generally, the taller, upright Phlox paniculata is best suited to full sun, part shade flower borders.
Low-growing Phlox subulate (creeping Phlox) is ideal for ground cover.
How big will it get
Depending on the type chosen, heights can vary from just 10cm up to 175cm.
How to plant Phlox
Dig the planting hole and add well-rotted compost or organic manure to the bottom before planting. Water the plant well before planting. Tease out the roots and plant at the same level as it was in its pot.
Firm the soil around the plant and water well at the base of the soil.
How to care for Phlox
Give these plants a feed in spring with an organic fertiliser.
Feeding weekly with a high potash fertiliser during the summer months should help increase the number of flowers produced.
Mulch around the base of the plant with a layer of well-rotted organic matter when the soil is moist. Autumn is the best time for this.
Do they spread?
The taller varieties tend to form clumps rather than spread. Low-growing types such as Phlox subulata (common name ‘creeping phlox’), will spread. And, for that reason, they are a great choice where ground cover is required.
How to keep it looking good
Split established clumps every three years to encourage rejuvenation.
Does Phlox need deadheading?
Deadheading spent flowers can encourage the plant to produce more flowers, especially if combined with a regular high-potassium feed.
Does it need pruning, and when should they be pruned?
Low-growing phlox do not need pruning other than tidying up dead flower stems. The flower stems of taller varieties can be removed down to the base level after flowering. Or the stems can be kept on throughout winter. Remove the leaves in this circumstance as they turn an attractive bronze colour.
How to propagate these plants
There are several ways to propagate them. Take basal cuttings in spring, divide the plant in spring or autumn or take root cuttings from the plant between autumn and winter.
What problems can Phlox have?
It can be susceptible to powdery mildew and grey moulds if overcrowded in soil that dries out. They have been known to be affected by leafy gall, a bacterial disease. This, fortunately, is seldom serious enough to necessitate taking action.
Phlox eelworm has in the past caused stems and leaves to distort and die back early without having flowered. But this now seems to be a rare occurrence.
Varieties of Phlox to have
Phlox ‘Bartwentynine’ is a classic, late summer flowering, cottage garden plant, good for planting mid-border. Its clusters of white flowers attract pollinating insects making it a good choice for wildlife-friendly gardens. Or, for scented, violet-blue flowers try Phlox paniculata ‘Blue Paradise’.
Phlox subulata is a low-growing, evergreen, mat-forming plant ideal for rockeries and raised beds. Commonly known as creeping phlox, it’s easy to grow if given the right conditions. It delights with masses of tiny flowers covering the plant between late spring and early summer.
Some phlox have adapted to grow well in dappled shade. Phlox divaricata is one such example, grows well in open woodland and has a loose, slightly straggly habit.
The annual, Phlox drummondii grandiflora ‘Brilliant’ will grow well in containers.
Best time of year to buy this plant
Deciduous types of phlox are available in most plant nurseries and Garden Centres from early summer until autumn, evergreen in theory year-round.
The best garden design style for this plant
Tall, upright plants work well in cottage garden style gardens, as well as a contemporary border combined with ornamental grasses. They also integrate well into a general mixed flower border.
Low-growing and mound-forming varieties are best suited to rockeries.
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David Domoney is a Chartered Horticulturalist, Broadcaster, and Author. David has worked with a number of the UK’s leading garden retailers as a plant buyer and strategic consultant. With more than 30 years experience, in horticulture, David is as passionate about plants now as he was when he bought his first plant at a village fete.
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