How To Grow Phlox
Phlox are easy-to-grow perennials that come back reliably every season. Phlox comes in two forms: Garden Phlox (Phlox paniculata) and Creeping Phlox (Phlox subulata). Both Garden Phlox and Creeping Phlox produce fragrant blooms that attract a variety of pollinators, including butterflies and hummingbirds.
Garden Phlox is an upright fragrant flower that grows to about three feet tall. It blooms in mid-summer and is a great addition to cottage garden landscapes, cutting gardens, and pollinator gardens. Its large flower clusters have a light, pleasant fragrance, and they make a lovely addition to summer bouquets.
Creeping Phlox is a low-growing groundcover with foliage that forms an attractive mat when flowers have passed. Creeping Phlox blooms in mid-spring. It looks great planted with spring-blooming bulbs, like Daffodils and Tulips, or as an edging plant, or planted on slopes or stone walls where it can spill over the edge.
When & Where to Plant Phlox
Phlox can be planted in spring or fall, and should be planted immediately upon receiving.
Light: Both varieties of phlox enjoy full sun, although the upright Garden phlox can take a little afternoon shade, particularly in the south.
Soil: Phlox is tolerant of most garden soils, but well-drained soil is preferable, particularly in northern areas where spring snow is slow to drain. Damp, waterlogged spring soil can rot the dormant roots. Add compost or peat moss to the garden to improve drainage and create a better overall environment.
Spacing: Garden phlox should be planted about 18 inches apart, while Creeping phlox should be planted about 2 feet apart. Giving these plants lots of room for air circulation is the key to limiting the appearance of mildew. (Although most varieties available today have been bred to resist mildew.)
Over the next few years you’ll see that both varieties form clumps that will gradually increase and join together to form one large grouping of phlox, with the Creeping variety creating a mat or carpet.
Planting in Fall: Fall plants can be kept cool on the deck for a few days until it’s convenient for you to plant, but don’t let the roots dry out and be sure to plant a few weeks before your first frost arrives.
Planting in Spring: Likewise, if the plant arrives in a container in spring, keep the container moist until the ground is ready to plant. Hold off on spring planting until the soil is free from melted snow and ice, and the ground is easy to work.
How to Grow Phlox Throughout the Season
Growth Habit: Each spring you will see the dormant crown of Garden phlox start to emerge from dormancy and produce small green leaves. Keep the area weed-free and let the phlox just grow. Eventually, tall stalks will begin to shoot skyward from the base of the plant.
After a few weeks of spring sunshine, the Creeping phlox will be covered with colorful blooms. Flowers continue to be produced until the weather turns to summer heat but you might well find a few flowers come back when cooler late summer or fall weather arrives.
Staking: The clump of Garden phlox emerges with bright-green leaves that stay low until spring is well established and then begins to grow upward stems. The stems are quite strong and rarely need staking unless the plant is in an area of high winds or where animals can knock the plant over. If you decide to stake, do so early in the year, when the plant is still low to the ground, rather than when flowers begin to form.
Watering: Although you’ll need to water young plants regularly until they become established, in general, phlox does not require much water. During seasons with regular rainfall, your phlox should not need any extra water from the gardener. This drought-tolerant perennial will struggle with water-logged soil, so practice restraint with your hose!
Fertilizing: An application of general garden fertilizer each spring or spreading a fresh layer of compost or fine mulch over the garden each spring is about all these delightful plants need.
Mulching: The low-growing Creeping phlox emerges around the same time as the Garden phlox, but its whole mat starts to show little green shoots which quickly grow to produce early greenery in the garden. Even in areas where the plant does not go completely dormant, you’ll see bright new growth emerge. For this reason, mulch very lightly, so as not to smother out its needle-like foliage.
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Phlox: End of Season Care
Trimming & Pruning: Deadheading the spent flowers of the summer blooming perennial keeps the plants healthy, and snipping off the flowers of the ground cover form keeps it looking neat. If you don’t have time or forget to deadhead or trim, the plants will forgive you and continue to bloom anyway. Each fall, after the frost has killed the top growth of your Garden phlox, trim the top dead growth and add that to the compost pile.
Trim the Garden phlox flowers and put into a vase on the table where they will hold up quite well for four or five days.
Dividing & Transplanting: Divide Garden phlox every 2-4 years in spring, to keep plants healthy and vibrant. Separate plants into sections, roots intact, with at least 3 active offshoots for replanting. Transplant with crowns one inch below the soil surface and eyes (offshoots) facing the sky.
Pests & Disease: Older varieties of Garden phlox can have mildew issues, particularly in areas with warm, humid summers. Plants growing in part shade are more likely to get issues than those in full sun, but even full sun locations cannot stop the mildew appearing on the plant. If you're not planting a mildew-resistant variety, your first line of defense against powdery mildew is to properly space your plants in order to allow for good air circulation. Use a botanical fungicide if the problem is persistent (and/or read the article below). Creeping phlox does not usually have fungal issues.
Grow Phlox: Design Advice
Garden phlox is a perfect addition to any perennial garden - even a native garden, as most phlox have not been bred too far away from their native roots. Plant taller varieties toward the back of the garden bed where their height will not block you from seeing smaller plants. They are perfect behind early blooming perennials such as Peonies which hide the early growth of the phlox stems. Phlox pairs nicely with contrasting flower types, such as spiky Russian Sage and the daisy-shaped blooms of Echinacea, Aster and Black Eyed Susan.
Plant spring-blooming bulbs with creeping phlox, and as the phlox spreads the bulbs will continue to emerge through the green mat for added spring delight.
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