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How to grow border phloxes

Val Bourne / 11 June 2013

Phloxes are garden stalwarts of the summer border, but they need rich, fertile soil to thrive so if your garden is dry, or your soil poor, you may fail. If you can grow them well they will delight you with their fragrance and form.

Phlox 'Eva Callum'
Phlox 'Eva Callum'

Border phlox colour can vary from almost-blue, to pure-white through to strident pink and the large domed heads can last for up to five weeks. Their fragrant flowers please bees and butterflies.

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Where to plant phloxes

Phloxes need good light and good soil, like many other plants with a North American provenance.

They enjoy hard winters too, also thanks to their North American origin, so hardiness is never a problem once plants are established.

How to plant phloxes

When planting, make sure that the soil is enriched with either garden compost or well-rotted manure. If this is in short supply dig in John Innes no. 3 compost to give the plants a boost.

Plant in groups of five or seven if you have room - for impact.

Most phloxes have woody stems and are self-supporting, but taller varieties will probably need staking in windy gardens.

When to deadhead phloxes

Deadhead phloxes regularly after flowering and some will repeat flower.

When to cut back

Cut the phox stems down in late autumn and tidy up the plants - especially any fallen leaves. Don't put this waste on the compost heap, bin it instead. This will reduce the risk of eel worm and mildew next year.

How to propagate phlox

Propagate border phloxes by division in early spring every four years or so. Separate into sections and plant out straight away, or pot up. It’s important to divide these plants as they tend to go backwards if left to their own devices for too long.

You can also pull rooted pieces from the edges of clumps and pot them up - these are called Irishman's cuttings.

Soft cuttings need to be taken in early summer. Use gritty compost.

Root cuttings can also be taken during winter. Cut two-inch sections, lay them flat in a seed tray, half full of compost, and then cover lightly. Keep the cuttings moist - but not wet.


You should feed your plants before mulching with a sprinkling of blood, fish and bone. Or you could surround them with well-rotted garden compost or manure to enrich the soil.

Pests and diseases

Slugs can be a problem early in the year so be vigilant.


Mildew affects phloxes badly and the leaves and stems become covered in white powder. It’s a water stress disease that plants often recover from in the following season.

The best way to avoid mildew is to mulch round your plants in early summer - being careful not to cover the crowns. This should always be done when the soil is warm and wet.

If you do have to water try to keep it off the foliage as splashes can encourage the spread of mildew. Try to allow the air to circulate through clumps - so don’t hem them in too much. Thin congested stems if needed.

Eel worm

Split stems and distorted and whip-like leaves can be caused by eel worm. You can either dig up your plants and destroy them, or you can take root cuttings in midwinter. The cuttings should be healthy.

Grow with…

Phloxes go well in a traditional mixed border with roses, penstemons and campanulas.

The domed heads also mix well with daisies and the blue varieties look more vibrant planted with warm-orange heleniums like 'Sahin’s Early Flowerer'. You could also use pinkechinaceas with paler phloxes.

Choosing phlox varieties

Phloxes have been bred over many years and varieties vary greatly in their garden worthiness. The following cultivars are all excellent.

A new American, award-winning phlox has bright-green leaves and fragrant white flowers. It was voted the American Perennial Plant Association Plant of the Year in 2002 because of its vigour and resistance to mildew. It was a chance seedling from the Brandywine River Museum in Pennsylvania, USA. (1991)

'Monica Lynden-Bell'
The prettiest pink phlox with dark buds and good heads of dainty-pink flowers - one of the top five.

'Blue Boy'
The nearest phlox with true-blue flowers: this looks stunning in evening light.

A strident phlox with pink-red flowers, but this resilient variety needs careful placing due to its colour.

'Franz Schubert'
Bred by Alan Bloom and named after his favourite composer, this lilac-blue phlox has large fragrant flowers.

Another Bloom phlox with variegated cream and green leaves topped by purple flowers - much better than 'Norah Leigh' in my opinion.

'Bright Eyes'
A pale-pink phlox with crimson-red eyes - resilient and mildew resistant.

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The opinions expressed are those of the author and are not held by Saga unless specifically stated. The material is for general information only and does not constitute investment, tax, legal, medical or other form of advice. You should not rely on this information to make (or refrain from making) any decisions. Always obtain independent, professional advice for your own particular situation.