Garden phlox or Phlox paniculata, a species of plants from the Polemoniaceae family, consists of a hundred or more cultivars. They are particularly valued for their large, enduring blooms and are native to parts of the eastern and central US. They are extensively cultivated as ornamentals in temperate regions and have become naturally established in other areas and have been introduced to other locations of the US, Canada, Asia, and Europe, other common names include tall phlox, perennial phlox, fall phlox, panicled phlox, and summer phlox.
These plants are upright herbaceous perennials, growing 47 inches tall or more and 39 inches wide, with simple, opposite green leaves on thin green stems, although there are several variegated cultivars with leaves of green edged by creamy white to yellow colors. The flowers are 0.5–1 inch in diameter, often mild to strongly aromatic, and produced in summer until autumn. The flowers are gathered in panicles of many branching stems, hence the label paniculata. Some cultivars start blooming during mid-summer, others during late August. Flower colors in wild species are normally pink or purple and rarely white.
However, several cultivars come in soft pastel to brilliant colors, ranging from lilac, lavender, purple, pink, salmon, and white, along with bi-colors with an “eye” in the middle of each flower with a contrasting edge. Their stems are sturdy, making them popular for use as cut flowers in vases.
Sometimes, their foliage is also very attractive, particularly with variegated cultivars. They are hardy and easy to maintain when growing in gardens. They are mostly pest-free and resistant to disease and can last for several years. These perennials attract butterflies and hummingbirds and can make your garden look very busy. They make excellent low-maintenance border plants for landscapes or home gardens.
They prefer full sun in temperate areas and partial sun in warmer climates.
They like their soil evenly moistened, but not over-watered. They don’t like drought as their foliage will wilt in hot or dry weather. They will perk up after they are watered. In warm weather, water the plants in the morning, giving the roots lots of water. Don’t overhead water these plants, particularly in temperate climates as this might cause problems such as powdery mildew. Keep the nozzle of the hose or watering can point at an angle that directs the spray towards the ground level at the soil. The leaves should be kept dry to prevent other fungal diseases.
They don’t like humidity as excessive humidity encourages diseases. Provide the plants with good ventilation in the warmer months.
These plants do not like hot, humid weather, so they are not a good selection for gardeners in hot climates. Some problems with heat and humidity can be mitigated by growing them under shade and mulching to cool the roots but they might not thrive as well when compared to plants growing in temperate climates.
They grow well in rich, moist soil with good drainage. Add compost if the soil is poor to provide nutrition and promote good drainage.
Plants growing in containers require good drainage and optimal growing conditions and get larger every year. They need repotting and divided in around 3 – 5 years to keep them growing healthy. Prepare a container filled 1/3 with potting mix since this is proven to drain well. Lift out the plant from its old home, transfer it to the prepared container, top-up empty spaces, and water it well. Avoid garden soil, which most likely will become compacted in containers. This can result in root rot caused by poor drainage, which can be deadly for the plant. Due to their height, they might require staking.
Propagation is mainly done by division although they can also be propagated by seeds, resulting seedlings won’t produce flowers in the same colors as the parent plant, generally producing pale magenta flowers.
Propagation by seed
You can directly sow seeds into the garden in spring after the soil can easily be dug up. Cover seeds with 1/8 inch of soil. Germination should happen in 5 – 10 days.
Propagation by division
The division is necessary to keep the plant healthy and is usually done when repotting or every 2 years or so in early spring. Dig the plant out either from the garden or from its container and split it apart by hand or with a sharp blade/knife. Every separated clump should have 3 – 5 healthy shoots attached to roots. Replant the clumps into your garden spaced apart by 18 inches to provide suitable air circulation or into containers.
If they’re growing in poor soil, feed them every spring with a slow-release fertilizer. However, if the soil is rich enough, adding compost in spring every year will provide them with all their nutritional requirements.
Deadheading spent flowers will help the plant produce more flowers during the season. Once the plants grow about 6 inches, remove all but 5 or 6 stems from each plant, then pinch off growing tips of the remaining stems to promote healthy growth, producing larger clusters of flowers and providing the plants with better air circulation. Regular weeding will prevent weeds from stealing nutrients or water, particularly in summer.
Since they attract bees and several other beneficial pollinators, avoid spraying the plants with herbicides or insecticides.
While these plants are relatively disease and pest-free, powdery mildew can be an issue, particularly in hot and humid summer weather. Symptoms consist of a white, powdery material appearing on top of the leaves. Severe infections can affect growth, make the leaves shrivel up, become brown or drop prematurely from the plant.
Leaf spots can also inflict bad damage, typically affecting lower leaves, where round, dark brown blotches or spots form. The spots can reach a diameter of 1/4 inch. Infected foliage curls, dries up, and dies.
Crown rot can also damage young plants, often making the foliage turn into a mushy mess around the soil line. This fungal disease typically shows up in periods of hot and humid weather. Symptoms include yellow, brown, and wilting leaves. The spores sometimes form a fluffy white material on infected stems and the surrounding soil.
Taking good care of your plants will help reduce the risk of disease. Remove dead foliage and water the plants early to let the leaves dry quicker. Mulching helps retain moisture but doesn’t place the material against plant tissue to avoid crown rot. Plants growing in shaded locations are more prone to get fungal diseases, so grow them in spots that get full sun. Keep plants 12 inches or more apart to allow plenty of sunlight and air circulation. Sunshine and good airflow help prevent fungal attacks.
Carefully remove infected leaves and destroy them as soon as any symptoms from these diseases appear, although fungicides don’t appear to prevent fungal infections from happening, horticultural oil, neem oil or jojoba oil applied to the foliage can help kill fungal pathogens when they appear. Always follow instructions for proper dilution and frequency of application.
Spider mites often attack plants in warm or dry weather. Symptoms appear as tiny brown spots under the leaves, including thin white webs between leaves. These insects pierce and suck sap and nutrients from foliage, resulting in wilting, turning leaves yellow or brown, and dropping. They rarely appear in cool weather and can be easily removed by spraying the plants early in the morning with insecticidal soap or, for severe infestations, a miticide specially meant for flowering plants.