Phlox: Types, Planting, Care and Preventing Powdery Mildew

Phlox is one of the most rewarding perennials: the lush, fragrant heads of garden phlox brighten the second half of summer, while creeping phlox turns a rock garden into a carpet of colour in spring. Here are the main types, how to plant them and how to keep the clumps free of powdery mildew.

Summer flowers in a bouquet: spray roses and chrysanthemums.

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Types of phlox

The genus Phlox (Polemoniaceae) has several dozen species, almost all native to North America. The Greek name means “flame”, after the bright flowers.

• Garden phlox (Phlox paniculata) is a tall perennial (60–120 cm) with large fragrant flower heads from July to September. It is also a good cut flower.
• Creeping phlox (P. subulata) is a low ground cover with needle-like leaves that disappears under flowers in May. Ideal for rock gardens.
• Woodland phlox (P. divaricata) is a spring phlox for part shade, with soft blue and lilac flowers.
• Annual phlox (P. drummondii) is an annual for beds and balconies that flowers all summer.

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Planting

• Plant in spring or in late summer to early autumn so the clumps can root before winter.
• Choose sun or light shade; flowering is weaker in deep shade.
• The soil should be fertile and moist but not waterlogged; dig in compost before planting.
• Space garden phlox about 50 cm apart: good air flow reduces disease.

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Care

• Watering. Phlox likes moisture: water generously in hot weather, at the base, keeping the leaves dry.
• Mulch. A layer of compost or bark keeps moisture in and protects the roots from overheating.
• Feeding. Nitrogen in spring for growth, then a flowering-plant fertiliser before blooming.
• Deadheading. Cut off faded heads; extra side shoots often follow.
• Dividing. Every 4–5 years lift and divide the clumps in spring or autumn, or the centre of the plant weakens.

Preventing powdery mildew

A white coating on garden phlox leaves in late summer is powdery mildew, the most common problem. Resistant cultivars, good spacing, watering at the base in the morning and thinning weak stems in spring all help. Remove affected leaves, and for severe cases use an approved fungicide according to the label.

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Phlox in bouquets

Garden phlox lasts about a week as a cut flower. Cut when about a third of the flowers are open, stand in cool water and remove faded flowers. Creeping phlox looks best in a rockery, and for more easy-care perennial ideas see “Low-maintenance garden”.

FAQ

Why are my phlox flowers getting smaller?

The clump has grown too big and exhausted the soil. Divide it and replant the young pieces in a new spot with compost.

Do phlox need winter protection?

Most species are hardy; in autumn cut garden phlox stems down and mulch the base with compost.

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Author: Maria Svitlovir

Graduated from Taras Shevchenko National University of Kyiv, Institute of Biology and Medicine (2001). BSc in Biology, MSc in Horticulture. Writes about plants, works at a garden centre selecting and repotting plants, and contributes to plant reference guides.