A summer flower garden would seem incomplete without border phlox, such is the character and beauty of the flowers. At a time when much of the garden is on the ebb, and could easily be dominated by shades of mustard-yellow, phlox provides cool pools of fresh colour to lift the spirit and provide a feast for insects.
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When I worked at Great Dixter, the Phlox paniculata on the Long Border had a special appeal on warm August evenings. Christopher Lloyd had accumulated a large collection that he would use in large, billowing swathes throughout the garden to great effect.
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- How to care for phlox
- When to plant Phlox
- When do phlox flower
- When to cut back phlox
- How to divide phlox
- Where to plant phlox
- How to propagate phlox
- Phlox problems
- The best phlox varieties
- Where to see and buy phlox
How to care for phlox
Phlox thrive in good, well-nourished soil that does not dry out too much during summer. Water is critical, but plants are less fussy about light – both full sun and part shade will do.
When to plant phlox
The best time to plant phlox is spring or autumn. They are best planted in groups where the conical flowerheads will make strong, undulating swathes of colour through the border. Planting in groups will add structure and stability to the planting, which is much needed in the garden when heading into autumn.
When do phlox flower
As they flower later in the summer, they rarely make the garden look untidy. Even before the phlox starts to flower, the foliage is lively and vibrant. Indeed, in spring the early mounds of phlox leaves make an excellent foil and verdant backdrop for tulip flowers. The foliage is also useful for masking unsightly allium leaves, or clothing the legs of roses, which can look bare and unattractive. Likewise, they can be planted at the front of the border where neatness is particularly important.
When to cut back phlox
Deadhead earlier-flowering cultivars such as Phlox paniculata ‘Rosa Pastell’ to prompt a second flush of flowers. Later flowering cultivars, however, are unlikely to produce another round of blossom.
Plants should be left up for autumn, until the stems are spent and dehydrated, before cutting back. At this point, they can be cleanly snapped off by using your feet to push them over.
How to divide phlox
To keep them flowering well, Phlox should be divided every three to four years, ideally in winter, before February, when they come into growth. Split the plants into decent chunks – about the size of a saucer – which will be substantial enough to give a good display in the first year.
Where to plant phlox
Phlox require rich, fertile soil and moisture during the growing season. If you’re trying to grow phlox in difficult, drought-prone soils, take extra care to enrich the ground with a good supply of compost during winter and follow up with thorough watering during summer and autumn.
Plant in full sun or part shade. Taller cultivars will need staking to prevent them from falling over. The best time to do this is a few weeks before they come into flower, with a strong cane and a ring of twine that incorporates the outer stems.
Plant into soil invigorated with a good dose of compost and mark their location. In spring, protect emerging shoots from competition from early bulbs and annuals, and water during dry spells.
How to propagate phlox
Phlox can also be propagated by stem cuttings, but there is a risk of transferring stem eelworm. The plants also propagate readily from root cuttings and as the eelworm do not invade the roots, this may be the safest course of action.
Phlox problems
Powdery mildew can be problematic in periods of extended drought. One or two protective sprays with a fungicide, such as Westland Fungus Guard, from mid-July to August is usually sufficient to protect our plants for the remainder of the growing season.
Stem eelworm (a nematode) is a more difficult problem. Affected plants will look stunted and chlorotic. The only remedy is to destroy any infected plants. The area can be replanted with a different species, but phlox should not be returned to the affected patch of ground for at least three years. As with most pests and diseases, prevention is easier than the cure, and new phlox acquisitions should be quarantined for the first year so the plant can be assessed before going into the border. This also allows the plants to bulk up a bit before having to compete with more established perennials in the border.
FACT FILE
What A genus of around 60 species, made up mostly of alpine and meadow perennials. There are a few annual species, but this feature focuses on the perennial border phlox Phlox paniculata and its hybrids.
Season Summer into early autumn.
Size Around 1-2m high with a spread of around 50cm.
Conditions Moist, fertile, acidic soils, but will tolerate other soil conditions if adequate moisture and compost are provided during the growing season.
Origins North America.
Hardiness Hardy throughout the UK, with an RHS rating of H7, and suitable for gardens in USDA zones 4a to 8b.
*Holds an Award of Garden Merit from the Royal Horticultural Society. † Hardiness ratings given where available.
The best phlox varieties
Phlox paniculata
The mother of the hybrid phlox, but few have the beauty and scent of the original. This one, propagated from a plant collected by Great Dixter’s Christopher Lloyd in the USA, has exquisite scent, colour and a rather wild habit. 1.8m x 50cm. RHS H7, USDA 4a-
Phlox x arendsii ‘Luc’s Lilac’
A good mid-border phlox with numerous small, powdery-lilac flowers, produced in cloud-like, conical heads. It’s a strong growing phlox so best divided every three years to maintain vigour. 1.2m x 50cm. AGM. RHS H7.
Phlox paniculata ‘Norah Leigh’
Its creamy-white, variegated foliage makes a useful contrast to the more usual greens. Nurserymen often opt for the greener forms as these grow more quickly, so look for plants with the most striking variegation. 1.4m x 50cm. AGM. RHS H7
Phlox paniculata ‘Rosa Pastell
An excellent cultivar with pink flowers, each with a pale-rose eye. These are held in trusses on strong stems and are particularly early. If it’s growing well, deadheading will prompt a second flush later in the summer. Height and spread: 1m x 50cm. AGM*. RHS H
Phlox paniculata ‘Elizabeth Arden’
Its soft pink hues complement silver-coloured plants such as Eryngium giganteum or Artemisia ‘Powis Castle’. Flowers are held on strong stems above green foliage. Does best in good, moist soil free from competition. 1.2m x 50cm. RHS H7
Phlox paniculata ‘Betty Marguerite’
Lipstick-pink flowers with petals that curve upwards on the edges to reveal paler undersides. This highlights each individual bloom and gives it a slightly dishevelled, but attractive look. An excellent border plant. 1.3m x 50cm.
Phlox paniculata ‘Starfire’
Large, carmine-pink flowers look fabulous atop very dark-green foliage, which emerges almost black and then stays a rich, aubergine purple until the flowers appear in late summer. 1m x 50cm. AGM. RH
Phlox x arendsii ‘Utopia’
A pretty phlox for the back of the border with loose panicles of soft mauve flowers. This phlox is a weak grower and resents competition in the spring, and also needs staking, but it is worth the effort.
2m x 50cm. AGM. RHS H7.
Phlox paniculata ‘Popeye’
An option for those who want the effect of a white phlox without the intensity of pure, brilliant white, which can sometimes be too glaring. It has a vague pink hue to the chalky white flowers. 1m x 50cm. RHS H7.
Phlox paniculata ‘Anne’
Sizable, chalky-white flowers with a soft mauvepink tinge. Has a long flowering season, from midsummer into early autumn, and has a good scent. Looks good with Agastache ‘Blue Fortune’. 1m x 50cm. AGM. RHS H7.
Phlox paniculata ‘Lichtspel’
In the Netherlands, this is affectionately known as the ‘bicycle phlox’ as the stems are said to be so strong you can park your bike in it. The flowers are scented and a pretty shade of mauvepink. 1.2m x 50cm. RHS H7
Phlox paniculata ‘Flamingo’
Produces early displays of pale-pink flowers with a distinctive dark eye. Blooms are held in dense trusses above clean foliage. Useful for the front of the border and good with cool blues. 1.2m x 50cm. AGM. RHS H7
Phlox paniculata ‘Butonik’
A Russian experiment where the bright lilac flowers never fully open, but are held in pointed buds just on the edge of unfurling. This cultivar looks quite unusual and always attracts attention from visitors. 1m x 50cm. RHS H7.
Where to see and buy phlox
- Dove Cottage Shibden Hall Road, Shibden, Halifax, West Yorkshire HX3 9XA. Tel 01422 203553, dovecottagenursery.co.uk
- Great Dixter Nursery Northiam, Rye, East Sussex TN31 6PH.
Tel 01797 254044, greatdixter.co.uk
•The Plant Specialist Whitefield Lane, Great Missenden,
Buckinghamshire HP16 0BH. Tel 01494 866650, theplantspecialist.co.uk