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Phlox glaberrima

Smooth Phlox

Family PolemoniaceaeGenus Phlox

Magenta-pink flowers with narrow tubes and flat spreading lobes, in a loose head on a wiry stem against gray rock.
FlowerMason Brock (Masebrock)Public domain

About the plant

What it is and where it grows — not part of any germination protocol.

The plant

Habit
Herbaceous Perennial, WildflowerExtension Gardener Plant Toolbox
Habit
perennialPlants of the World Online
Height
2-4 ft0.6-1.2 mExtension Gardener Plant Toolbox
Spread
2-2.5 ft60-75 cmExtension Gardener Plant Toolbox
Flower
Pink, Purple/Lavender, Red/Burgundy, WhiteExtension Gardener Plant Toolbox
Blooms
Spring, SummerExtension Gardener Plant Toolbox
Native range
Native to the lower 48 statesPLANTS Database
Hardiness zones
3-8Extension Gardener Plant Toolbox

Growing conditions

Sun
Full sun; Partial ShadeExtension Gardener Plant Toolbox
Soil
Clay, High Organic Matter, Loam (Silt), SandExtension Gardener Plant Toolbox
Soil pH
Acid (<6.0), Neutral (6.0-8.0)Extension Gardener Plant Toolbox
Moisture
Good Drainage, Moist, Occasionally WetExtension Gardener Plant Toolbox
Watering
Drought tolerance: LowPLANTS Database

Toxicity is noted only where a source states it. No note here is not a finding of safety.

Sources: Extension Gardener Plant Toolbox — NC State Extension; Plants of the World Online — Royal Botanic Gardens, Kew; PLANTS Database — USDA NRCS.

Worth knowing

  • Smooth phlox grows in moist to wet prairies and forests, where it is a sign of high-quality habitat. How it relates to Phlox carolina and Phlox maculata is particularly unclear. Wikipedia: Phlox glaberrima

This source reports 5 treatments. All are shown.

Protocol 1

DerivedN. C. Deno, 1993

Difficulty Moderate Rated by us, not by the source.

Start around June 29, 2027 for a May 3 last frost. Too late for spring 2027 — that needed starting on June 28, 2026.

  1. Dry storage

    Duration: 180 daysTemperature: 70°F 21°C

  2. Cold moist stratification

    Duration: 90 daysTemperature: 40°F 4°C

  3. Warm moist stratification

    Duration: 90 daysTemperature: 70°F 21°C

about 9 months from start to step 3. Germination happens during step 3, in 11 days.

71% germination in 3–11 days.

Seed Germination Theory and Practice, 2nd ed. — N. C. Deno, 1993 · Ch. 20, Phlox p. 191Public domain
Show the original text
Phlox (Polemonlaceae). Phlox seed is hard to collect as there are only a few seed in each spherical capsule and these capsules roll away as soon as ripe. As a result seed of Phlox is not readily available except for the annual P. glaberrima germ. 70(27% in 4-11 w)-40-70(20%)-40-70(13%) and 40- 70(1 1%)-40(9%)-70(16%)-40(2%). Seed DS 6 m at 70 germ. 70(50% in 5th w)-40- 70(8%) and seed DS 6 m at 40 germ. 70(57% in 2-9 w)-40(3%)-70(3%) and 40- 70(71% in 3-11 d).
Seed Germination Theory and Practice, 2nd ed., Ch. 20, Phlox p. 191. Quoted exactly. Every value on this card comes from this record, except the difficulty rating, which is ours; the step names come from a fixed list.

Protocol 2

DerivedN. C. Deno, 1993

Difficulty High Rated by us, not by the source.

Start around August 6, 2027 for a May 3 last frost. Too late for spring 2027 — that needed starting on August 5, 2026.

  1. Dry storage

    Duration: 180 daysTemperature: 70°F 21°C

  2. Warm moist stratification

    Duration: 90 daysTemperature: 70°F 21°C

  3. Cold moist stratification

    Duration: 90 daysTemperature: 40°F 4°C

    3 germinated in this phase.

  4. Warm moist stratification

    Duration: 90 daysTemperature: 70°F 21°C

    3 germinated in this phase.

Steps after step 2 run on after germination.

about 6 months from start to step 2. Germination happens during step 2, in 63 days.

57% germination in 14–63 days.

Seed Germination Theory and Practice, 2nd ed. — N. C. Deno, 1993 · Ch. 20, Phlox p. 191Public domain
Show the original text
Phlox (Polemonlaceae). Phlox seed is hard to collect as there are only a few seed in each spherical capsule and these capsules roll away as soon as ripe. As a result seed of Phlox is not readily available except for the annual P. glaberrima germ. 70(27% in 4-11 w)-40-70(20%)-40-70(13%) and 40- 70(1 1%)-40(9%)-70(16%)-40(2%). Seed DS 6 m at 70 germ. 70(50% in 5th w)-40- 70(8%) and seed DS 6 m at 40 germ. 70(57% in 2-9 w)-40(3%)-70(3%) and 40- 70(71% in 3-11 d).
Seed Germination Theory and Practice, 2nd ed., Ch. 20, Phlox p. 191. Quoted exactly. Every value on this card comes from this record, except the difficulty rating, which is ours; the step names come from a fixed list.

Protocol 3

DerivedN. C. Deno, 1993

Difficulty High Rated by us, not by the source.

Start around September 3, 2027 for a May 3 last frost. Too late for spring 2027 — that needed starting on September 2, 2026.

  1. Dry storage

    Duration: 180 daysTemperature: 70°F 21°C

  2. Warm moist stratification

    Duration: 90 daysTemperature: 70°F 21°C

  3. Cold moist stratification

    Duration: 90 daysTemperature: 40°F 4°C

  4. Warm moist stratification

    Duration: 90 daysTemperature: 70°F 21°C

    8 germinated in this phase.

Steps after step 2 run on after germination.

about 6 months from start to step 2. Germination happens during step 2, in 35 days.

50% germination in 35 days.

Seed Germination Theory and Practice, 2nd ed. — N. C. Deno, 1993 · Ch. 20, Phlox p. 191Public domain
Show the original text
Phlox (Polemonlaceae). Phlox seed is hard to collect as there are only a few seed in each spherical capsule and these capsules roll away as soon as ripe. As a result seed of Phlox is not readily available except for the annual P. glaberrima germ. 70(27% in 4-11 w)-40-70(20%)-40-70(13%) and 40- 70(1 1%)-40(9%)-70(16%)-40(2%). Seed DS 6 m at 70 germ. 70(50% in 5th w)-40- 70(8%) and seed DS 6 m at 40 germ. 70(57% in 2-9 w)-40(3%)-70(3%) and 40- 70(71% in 3-11 d).
Seed Germination Theory and Practice, 2nd ed., Ch. 20, Phlox p. 191. Quoted exactly. Every value on this card comes from this record, except the difficulty rating, which is ours; the step names come from a fixed list.

Protocol 4

DerivedN. C. Deno, 1993

Difficulty High Rated by us, not by the source.

Start around January 18, 2027 for a May 3 last frost.

  1. Warm moist stratification

    Duration: 90 daysTemperature: 70°F 21°C

  2. Cold moist stratification

    Duration: 90 daysTemperature: 40°F 4°C

  3. Warm moist stratification

    Duration: 90 daysTemperature: 70°F 21°C

    20 germinated in this phase.

  4. Cold moist stratification

    Duration: 90 daysTemperature: 40°F 4°C

  5. Warm moist stratification

    Duration: 90 daysTemperature: 70°F 21°C

    13 germinated in this phase.

Steps after step 1 run on after germination.

Germination happens during step 1, in 77 days.

27% germination in 28–77 days.

Seed Germination Theory and Practice, 2nd ed. — N. C. Deno, 1993 · Ch. 20, Phlox p. 191Public domain
Show the original text
Phlox (Polemonlaceae). Phlox seed is hard to collect as there are only a few seed in each spherical capsule and these capsules roll away as soon as ripe. As a result seed of Phlox is not readily available except for the annual P. glaberrima germ. 70(27% in 4-11 w)-40-70(20%)-40-70(13%) and 40- 70(1 1%)-40(9%)-70(16%)-40(2%). Seed DS 6 m at 70 germ. 70(50% in 5th w)-40- 70(8%) and seed DS 6 m at 40 germ. 70(57% in 2-9 w)-40(3%)-70(3%) and 40- 70(71% in 3-11 d).
Seed Germination Theory and Practice, 2nd ed., Ch. 20, Phlox p. 191. Quoted exactly. Every value on this card comes from this record, except the difficulty rating, which is ours; the step names come from a fixed list.

Protocol 5

DerivedN. C. Deno, 1993

Difficulty High Rated by us, not by the source.

Start around June 19, 2027 for a May 3 last frost. Too late for spring 2027 — that needed starting on June 18, 2026.

  1. Cold moist stratification

    Duration: 90 daysTemperature: 40°F 4°C

  2. Warm moist stratification

    Duration: 90 daysTemperature: 70°F 21°C

  3. Cold moist stratification

    Duration: 90 daysTemperature: 40°F 4°C

    9 germinated in this phase.

  4. Warm moist stratification

    Duration: 90 daysTemperature: 70°F 21°C

  5. Cold moist stratification

    Duration: 90 daysTemperature: 40°F 4°C

    2 germinated in this phase.

Steps after step 4 run on after germination.

about 9 months from start to step 4. Germination happens during step 4; time not stated, 21 days assumed.

16% germination.

Seed Germination Theory and Practice, 2nd ed. — N. C. Deno, 1993 · Ch. 20, Phlox p. 191Public domain
Show the original text
Phlox (Polemonlaceae). Phlox seed is hard to collect as there are only a few seed in each spherical capsule and these capsules roll away as soon as ripe. As a result seed of Phlox is not readily available except for the annual P. glaberrima germ. 70(27% in 4-11 w)-40-70(20%)-40-70(13%) and 40- 70(1 1%)-40(9%)-70(16%)-40(2%). Seed DS 6 m at 70 germ. 70(50% in 5th w)-40- 70(8%) and seed DS 6 m at 40 germ. 70(57% in 2-9 w)-40(3%)-70(3%) and 40- 70(71% in 3-11 d).
Seed Germination Theory and Practice, 2nd ed., Ch. 20, Phlox p. 191. Quoted exactly. Every value on this card comes from this record, except the difficulty rating, which is ours; the step names come from a fixed list.

How each step is done, in Deno’s words, and what Verified and Derived mean.

Germination trials

Readers’ own records of sowing this species, published after review. Share your trial · All trials

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