Phlox are herbaceous plants that bear a profusion of small, often scented flowers in summer. They range from tall border perennials to creeping phlox or alpine varieties and woodland types, as well as annual varieties that can be grown as bedding.
Phlox paniculata is the most commonly grown garden phlox, often known as border phlox. In the wild, Phlox paniculata can grow to nearly 2m, and typically bears pink phlox flowers. Years of breeding have resulted in shorter, more garden-worthy cultivars that flower in a variety of different colours, including shades of blue, purple, pink, magenta, red and white. As well as being fragrant and long-flowering, most cultivars attract a variety of bees and other pollinating insects.
Phlox are herbaceous border stalwarts – hardy and very easy to grow. They have sturdy stems, so even the taller varieties rarely need staking. Largely pest-free and disease-resistant, they last for years in the garden. They are excellent, low-maintenance plants for a herbaceous border or cottage garden and combine well with other herbaceous perennials such as delphiniums, campanulas and red hot pokers. For a more contemporary look, combine them with ornamental grasses. They make excellent cut flowers.
Most border phlox grow best in full sun, but as they are native to woodland edges they will also do well in partial shade.
Cultivars of creeping phlox or alpine phlox, such as Phlox subulata, are low growing and flower in early summer. They thrive in full sun and well-drained soil. They make excellent ground cover and are often grown in a rockery. Varieties that hail from woodland habitats, sometimes called ‘woodland phlox’, such as Phlox divaricata, need partial shade and hummus-rich soil. Annual phlox, such as Phlox drummondii, are ideal as bedding plants or for growing in containers and are often grown from seed.
How to grow phlox
Most border phlox do well in a sunny spot in moist, well drained soil. They are sensitive to drought, so them keep well watered in hot, dry weather. They need little care, although deadheading promptly may result in more phlox flowers later in the season, and dividing every few years will keep the plant healthy and flowering well. Alpine phlox need plenty of sun and well drained soil. Woodland phlox need shadier conditions.
Phlox: jump links
- Where to grow phlox
- How to care for phlox
- How to propagate phlox
- Phlox problem-solving
- Phlox buying advice
- Varieties of phlox to grow
Where to grow phlox
Grow your phlox in a sunny spot or in partial shade, in moist but well-drained soil. Taller varieties are suitable for the back or middle of a border, shorter varieties at the front.
How to plant phlox
Plant phlox in spring or autumn, while the soil is warm and moist. Phlox don’t do well on dry, well drained soils, such as sandy soil, so improve with organic matter, such as garden compost or well-rotted manure, before planting and then mulch afterwards, too.
How to care for phlox
Phlox gradually form large clumps in the garden. To keep your plant growing well and to prevent it from becoming congested, divide it every three or four years, in early spring. Replant the clumps around 60cm apart. Signs that your phlox needs dividing are fewer flowers and a sparse centre.
If you’re gardening on poor soil, feed every spring with fertiliser.
Deadheading immediately after flowering might result in more phlox flowers produced from side shoots in autumn.
Plants rarely need staking, but you may need to do this on a windy site.
If you want to stagger flowering or delay flowering, you can try the ‘Chelsea Chop’ on your plants. Cut some or all of the stems back by half in late May, around the traditional time of the RHS Chelsea Flower Show. Cut on the diagonal, just above a leaf joint. This will delay flowering by about a month.
Cut your plant down to ground level in autumn or winter, once the foliage has died back.
How to propagate phlox
You can increase your stock of phlox plants is by dividing them in early spring. Dig up the plant and split it into smaller chunks before replanting. These new plants will go on to flower in summer. Plant the new plants 60cm apart.
You can also propagate phlox by taking root cuttings in winter, before they start to send up their spring shoots. Use plants dug up from the garden or pot-grown plant. Place the pots of cuttings in a cold frame, where they’ll root and grow into new young plants by midsummer. They will then flower the following year.
Remove a few of the largest roots, as close to the base of the stem as possible, where’s there’s plenty of tissue ready to produce shoots.
Make the cuttings about 4cm long and take a nick out of the base (the end furthest from the root tip) so you know which way up they should be planted.
Insert the full lengths of root vertically into firmed compost, nicked end at the top, then cover with a good layer of grit and water in. Each cutting should produce a shoot in spring.
Growing phlox: problem solving
Phlox don’t like drought – you may notice the foliage wilting in dry weather. Your plant should perk up after it has been watered. In hot weather, water in the morning, making sure plenty of water reaches the roots.
Powdery mildew can be a problem in hot, humid weather, especially if your plant is growing in partial shade. If this tends to be a problem in your garden, improve air circulation by thinning the plants in early spring.
Advice for buying phlox
- Most phlox need moist but well drained soil and a sunny spot, so make sure you have the right conditions in your garden
- You can buy container-growin phlox all year round at garden centres and nurseries. You can also buy bare-root plants in winter – this is a cheaper option
- For the widest variety of plants, go to a specialist nursery or online supplier
Where to buy phlox online
Varieties of phlox to grow
Phlox paniculata ‘Purple Eye Flame’
Phlox paniculata ‘Purple Eye Flame’ has fragrant purple flowers with a white eye. It’s well suited to growing towards the front of a mixed or herbaceous border among daisies and echinaceas, or even in containers.
H x S: 40cm x 40cm
Phlox paniculata ‘Pina Colada’
Another perennial border phlox, Phlox paniculata ‘Pina Colada’ is a short-growing phlox, bearing large domed heads of pure white flowers. It’s perfect for growing in a night garden or near a seating area, where you can sit and enjoy its intense fragrance on summer evenings.
H x S: 75cm x 50cm
Phlox paniculata ‘Blue Paradise’
Phlox paniculata ‘Blue Paradise’ is a gorgeous border phlox, bearing fragrant, violet flowers with a faint paler patch and dark eye. Reaching heights of 120cm, it’s perfect for growing at the back of the border, where it works well with blooms of a similar colour.
H x S: 120cm x 45cm
Phlox divaricata subsp. laphamii ‘Chattahoochee’
This woodland phlox bears compact, spreading carpets of lilac-blue flowers in June, over fresh green, hairy phlox leaves. It’s ideal for growing in large clumps at the edge of a border or beneath deciduous trees. The Royal Horticultural Society has given it its prestigious Award of Garden Merit.
H x S: 35cm x 50cm
Phlox drummondii ‘Moody Blues’
Phlox drummondii ‘Moody Blues’ is an annual phlox that’s widely grown as a summer bedding plant. Its spreading habit makes it perfect for filling gaps at the front of a border, or forming part of a summer container display. It has a compact, bushy habit and bears flowers in a variety of shades of blue. Seeds are widely available.
H x S: 25cm x 30cm
Phlox subulata ‘McDaniels Cushion’
Moss phlox, Phlox subulata, is a spreading evergreen perennial growing to a height of just 15 cm. It bears small flowers in shades of pink, purple and white, from spring to early summer. Phlox ‘McDaniels Cushion’ forms a low, spreading carpet of slender, mid-green leaves and bears masses of pretty pink or purple flowers in summer.
H x S: 15cm x 50cm