Don’t Risk Next Year’s Blooms — When and How to Cut Back Phlox the Right Way

If your phlox plants look bedraggled or you’ve been dealing with mildew issues year after year, it may be time to pick up your pruners. Pruning phlox of any sort before winter can prevent powdery mildew and it enhances flowering, too.

No matter what variety of phlox is growing in your garden, this guide will help you determine exactly when to cut back phlox for improved growth and better blooms.

When Should You Cut Back Phlox?

Cutting back phlox plants at the wrong time of the year can remove flower buds and reduce blooming. But when exactly should you prune phlox? The answer depends on what type of phlox you’re growing.

• Creeping phlox (Phlox subulata) does most of its blooming in spring. Prune it as soon as the plant finishes flowering in late spring to early summer.
• Tall phlox (Phlox paniculata), on the other hand, flowers later in the season with peak blooming occurring between mid-summer and early autumn. Major pruning should be reserved for fall.

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How to Cut Back Phlox

For Tall Phlox

Lightly pruning tall phlox before its flower buds form can make your plants bushier.

1. Cut stems. To start, cut away up to 1/3 of the stems on your tall phlox to improve airflow.
2. Pinch by the nodes. Then pinch back the plants’ growing stem tips to a leaf node to encourage branching.
3. Pinch away dead flowers. Throughout summer, pinch or cut away any faded flowers on your tall or creeping phlox to make your plants look tidier and extend their bloom time.
4. Cut tall phlox down in the fall. To prune tall phlox in fall, wait until a killing frost turns your plants brown, and then cut your plants off at the soil line. This is critical if you want to keep mildew from spreading; it will help your plants come back stronger in spring.

For Creeping Phlox

Because creeping phlox isn’t as susceptible to powdery mildew as tall phlox, it doesn’t necessarily need to be pruned at all. But if you want to improve the shape of your plants and help them flower more, follow these steps.

1. Prune back by up to 1/3 when the plants finish flowering between late May to mid-August.
2. Throughout summer, pinch or cut away any faded flowers. Wait until half of the plant’s flowers have faded and then trim all the dead flowers in one go.

Can You Cut Back Phlox in the Spring?

Although tall phlox can technically be pruned in spring, pruning phlox in fall is your best bet if you want to keep mildew out of your garden.

Compared to most perennials, tall phlox is particularly susceptible to powdery mildew, and leaving infected plants in your garden through winter increases the chances that spring shoots will be reinfected with mildew spores.

Thoroughly pruning phlox in autumn can interrupt the lifecycle of mildew spores, and it’s even more effective if you follow up your pruning with a few preventative applications of a milk or baking soda spray in spring.