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growing phlox from seed

Oh, For Phlox Sake! Growing Phlox from Seed

It's time to hose out your favorite hanging planters and order some seeds! Phlox is, universally, one of the most popular ornamentals for hanging baskets, large pots, and cottage garden beds. Plus, the name gives you a great opportunity come up with rude and inappropriate puns.

Phlox is very easy to grow and maintain, and once it's established, it's fairly drought-tolerant. It's a great choice for homeowners who want to grow something to cheer up front porches and patio gardens, but who aren't inclined to obsess over their plants. (In other words, "tourists" in the world of rabidly-obsessed gardening).

Origins and cultural history

The phlox family (Polemoniaceae) is native to North America, and there are species indigenous to most of our continent's regions and climates. Nearly all phlox species and cultivars adapt outside their home territories.

Intrepid Scottish naturalist, botanist, and explorer Thomas Drummond (1790-1835) is the first European to catalog the species that now bears his name. He shipped specimens from Texas to England in 1835 while on an expedition through the American Southwest, and in Great Britain phlox earned widespread adoration as an "exotic" garden specimen. Amateur English botanist Sir W. J. Hooker wrote that varieties of the newly-discovered petunia as well as P. drummondii, the phlox species named for the Scot, "were decidedly among the greatest ornaments of the greenhouse in the Glasgow Botanic Garden during the month of May (1836), a season too early for them to come to perfection in the open border."

Cultivated varieties made the round trip back to American gardens but Drummond, however, would never return; the same year he sent phlox and hundreds of other plant and animal specimens back to the U.K, he passed away on the Cuban leg of his collection tour.

Phlox is Latin for "fire" or "flame," and the red annual phlox varieties truly live up to the name. In the Victorian language of flowers, phlox represented sweet dreams and declarations of love.

Various phlox species native to different North American climates had medicinal value among First Nation cultures. Specific parts or entire plants, used internally or externally, treated the following:

  • Cold symptoms
  • Body aches
  • Stomach aches
  • Diarrhea
  • Eczema
  • Eye irritation
  • Nerve numbness
  • Venereal disease (there's a joke in here somewhere)

We here at Seed Needs recommend that our customers do plenty of their own research (including a shout-out to their doctors) before medicinally administering plants. These applications are attributed to the Polemoniaceae family in general, without regard to individual species.

General phlox types

We've selected the most popular phlox varieties for our catalog, with more to come in the future. It's easy to provide a broad overview of the Polemoniaceae because most phlox species tend to have the same—or very similar—care requirements, though they may vary in seasonal classification and foliage texture. The annuals grow well in USDA hardiness zones 3 through 10, while the perennial varieties successfully overwinter in zones 4 through 8. Our phlox seed packets and catalog profiles can tell you more about each species' individual needs.

Phlox are multi-branching plants with clusters of 1", five-petaled blooms on terminal spikes. The flowers are somewhat trumpet-shaped, but with separate petals and a short throat. A few specimens have ragged-edged petals. Most phlox share the same range in bloom colors, including magenta, pink, lavender, white, or peach, though some cultivars are blue or purple. The blooms in some varieties are bi-colored, and most have a degree of shading.

Except for those belonging to the mountain phlox, leaves are ovate to spear-shaped, 1" to 3" long, and vivid green. Upper leaves grow in an alternating pattern, while the lower leaves grow in an opposite fashion. Phlox have glandular, sometimes hairy, sap-emitting stems, so those who hate getting their fingers sticky might want to wear nitrile or gardening gloves.

You'll find most annual and perennial phlox growing in low-profile, sprawling, colorful drifts along garden borders or in mass-planted beds. Some phlox, including "tall phlox," are upright with a more columnar habit.

Phlox drummondii

  • Annual phlox
  • Drummond('s) phlox

Annual phlox is the most widely-used species in the family, growing 8" to 20" tall and wide. It's nearly identical to perennial phlox (Phlox paniculata), and one is often mistaken for the other.

Linanthus grandiflorus

  • Mountain phlox
  • Largeflower desert trumpets
  • Largeflower linanthus
  • Large flowered leptosiphon

An annual with whorled, needle-like foliage that resembles piney green bottle-brushes. Flowers grow individually or in clusters at the ends of tall stems. Mountain phlox grows 1" to 3" tall, and is native to the scrubby coastal hills of western California, from the San Francisco South Bay to Santa Barbara.

Phlox paniculata

  • Garden phlox
  • Perennial phlox

Growing 2' to 4' tall, and 2' to 3' wide, this perennial adds a bit more altitude to the phlox garden. P. paniculata is a native to the Eastern US, from New York to northern Georgia and most states east of the Missouri river.

Phlox in the garden

These plants don't need much coddling, and in fact, they thrive with a bit of neglect as long as you provide their preferred growing environment. While these guidelines focus on annual phlox species, perennial garden phlox (Phlox paniculata) requirements are nearly identical. Annual varieties are spring bloomers, fading out in mid-summer. Perennials pick up the mantle in July, blooming through September. All phlox are nectar-rich, attracting butterflies, bees, and hummingbirds!


While container plants tend to dry out faster than those grown in beds, and therefore should be watered more frequently, phlox withstands short periods of drought. Still, we recommend consistently moist soil when possible.

Sunlight and heat

Phlox is a sun-loving plant, but it likes a little afternoon shade in the hottest climates. Ceramic containers tend to absorb a lot of heat, so we recommend placing potted phlox where it can be out of the sun in late afternoon.

Peak summer temperatures will cause annual phlox to turn brown and drop its flowers, but if you deadhead them and cut the stems back by about 60%, chances are good they'll get a second wind later in the season.

Soil preferences

Don't fuss too much about soil quality. Phlox thrives in poor to medium soils, as long as it drains well. You can plant it in consistently-irrigated beds, too, with careful spacing. Prepare the soil with plenty of aged compost to improve drainage, and throw in a little peat moss or similar acidic material; phlox likes its soil on the slightly acidic side with a general pH between 6.0 and 8.0.

Phlox is one of the few plants that grow well near black walnut trees.

Maintenance, pests, and diseases

Phlox is fairly disease and pest-hardy in its ideal garden environment. It's also deer and rabbit resistant. Don't be alarmed by the following list of potential issues, because proper spacing, ground-level watering, and planting in full sun will prevent most of these problems.

  • Leaf spot
  • Crown rot
  • Root rot
  • Mildew
  • Caterpillars
  • Leaf miners
  • Two-spot spider mites

Clean up and destroy any diseased or dropped plant matter to prevent disease spread. Mulching will help retain moisture and moderate soil temperatures, but be sure to keep mulch away from the plant stems. At the end of the season, cut back annual phlox to soil level. Cut perennial phlox 2" above the soil level, and clean up any debris; it will regrow again in the spring.

Growing phlox from seed

Phlox germinates and develops quickly, so in most cases you're best off direct-sowing your seeds…but if spring comes late to your neighborhood, start them indoors in a sunny window. Growing lights and heat mats always help when growing phlox from seed.

  • Seed Treatment: None required.
  • When to Plant Outdoors: As soon as the soil is consistently 65°F to 70°F.
  • When to Plant Indoors: 6 to 8 weeks prior to last spring frost.
  • Seed Depth: ⅛"; some sunlight required to germinate.
  • Seed Spacing: Plant or thin 1' apart in dryer conditions; 2' in humid regions or when planting in consistently-irrigated beds.
  • Days to Germination: 5 to 10 days at 70°F; 7 to 14 days at 65°F.
  • Transplanting Tips: Harden off for a few days prior to transplanting. If using biodegradable pots, score and moisten before placing the entire container into the bed or pot.

Be sure to keep your planting beds consistently moist with a mist sprayer or gentle hose setting. Once the plants have grown a few pairs of true leaves, you can scale back watering unless the phlox variety requires otherwise.  

Floral design with phlox

Phlox's clustered flowers are popular among florists, and they're often used as filler in informal, "cottage garden" themes. There's nothing stopping you from making phlox flowers the main event! They last 7 to 10 days as fresh-cut flowers if they're placed in water immediately after harvesting. Cut as much of the stem as possible to add height to your arrangement; the leaves, especially those of mountain phlox, are a part of the plant's appeal.

We give a... Well, let's just say we really care

When you're ready to brighten up your garden, contact us! With free shipping and handling for orders over $18, you can quite literally give flying phlox to a friend (As in flying foxes. We're professionals here.) All our seed packets come with detailed instructions and collectable designs, and we take customer service seriously. Be sure to bookmark our gardening blog for plant spotlights and growing tips!
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