Plants · Flowers
Garden phlox planting zones
Garden phlox (Phlox paniculata and the tall phloxes) is a perennial. By the type table below, at least one type lives through winter in the ground in 4a–9a; outside those zones, none of the types on this page is rated. Below the types are the dates its year turns on: each zone’s median last spring freeze and first fall freeze, from NOAA records.
Published October 26, 2026 · Cite this page
The types
Which garden phlox to grow
| Type | Hardy in the ground | Notes |
|---|---|---|
| Garden phlox, mildew-resistant cultivars Phlox paniculata (e.g. ‘Jeana’, ‘David’, ‘Robert Poore’, ‘John Fanick’, ‘Delta Snow’) | 4a to 8b, then too hot or humid | Iowa State and Clemson both name ‘David’ and ‘Delta Snow’ for mildew resistance. Clemson calls ‘John Fanick’ very drought and heat tolerant. |
| Garden phlox, other cultivars Phlox paniculata hybrids | 4a to 8b, then too hot or humid | Penn State rates garden phlox zones 4–8 and NC State 4a to 8b. Clemson says many cultivars are the most prone to powdery mildew. |
| Spotted phlox Phlox maculata (e.g. ‘Natascha’, ‘Rosalinde’) | 4a to 7b, then too hot or humid | Earlier flowering and better mildew resistance than garden phlox (Iowa State). Clemson says it is best suited to the Piedmont and mountains. |
| Carolina phlox Phlox carolina (e.g. ‘Magnificence’, ‘Gypsy Love’) | 5a to 9a, then too hot or humid | Clemson: native throughout the Southeast, heat tolerant, grows throughout South Carolina. It blooms earlier than garden phlox. |
Zone ranges are a judgement: horticultural convention set beside what the sources below say, not a measurement. In the next table the freeze dates are measured, and the count of hardy types comes from these judged ranges.
Zone by zone
Where garden phlox lives through winter, and when the freezes fall
Each date is the median across every NOAA station the zone’s ZIP codes cite, 1991–2020 normals. The middle half of those stations falls within the range shown beside it.
| Zone | Types hardy in the ground | Last spring freeze | First fall freeze |
|---|---|---|---|
| 3a | 0 of 4 | only 10 stations with comparable freeze dates — too few to publish a date | |
| 3b | 0 of 4 | May 18 · middle half May 15 – May 25 | September 23 · middle half September 17 – September 26 |
| 4a | 3 of 4 | May 15 · middle half May 10 – May 21 | September 27 · middle half September 22 – September 30 |
| 4b | 3 of 4 | May 11 · middle half May 5 – May 23 | September 30 · middle half September 23 – October 3 |
| 5a | 4 of 4 | May 9 · middle half May 1 – May 20 | October 2 · middle half September 26 – October 7 |
| 5b | 4 of 4 | May 4 · middle half April 27 – May 15 | October 8 · middle half October 1 – October 14 |
| 6a | 4 of 4 | May 1 · middle half April 24 – May 9 | October 14 · middle half October 5 – October 20 |
| 6b | 4 of 4 | April 25 · middle half April 17 – May 3 | October 20 · middle half October 11 – October 24 |
| 7a | 4 of 4 | April 19 · middle half April 11 – April 27 | October 23 · middle half October 17 – October 28 |
| 7b | 4 of 4 | April 8 · middle half April 3 – April 16 | October 30 · middle half October 25 – November 3 |
| 8a | 3 of 4 | March 30 · middle half March 25 – April 5 | November 5 · middle half November 1 – November 10 |
| 8b | 3 of 4 | March 20 · middle half March 13 – March 29 | November 12 · middle half November 7 – November 18 |
| 9a | 1 of 4 | March 5 · middle half February 24 – March 15 | November 24 · middle half November 18 – December 2 |
| 9b | 0 of 4 | February 12 · middle half January 30 – February 25 | December 8 · middle half December 1 – December 17 |
| 10a | 0 of 4 | 107 of 190 stations here record no ordinary freeze, so there is no freeze date to count from | |
| 10b | 0 of 4 | 70 of 79 stations here record no ordinary freeze, so there is no freeze date to count from | |
| 11a | 0 of 4 | 34 of 34 stations here record no ordinary freeze, so there is no freeze date to count from | |
| 11b | 0 of 4 | 12 of 12 stations here record no ordinary freeze, so there is no freeze date to count from | |
“Types hardy in the ground” is a judgement, from the type table above. The freeze dates are measured.
A zone does not tell you your own dates. Inside a single zone the median last spring freeze still varies by 34 days from station to station, so the box below gives the dates of the NOAA station nearest your ZIP code.
Your ZIP code
Your ZIP, your answer
Enter your ZIP code to see your USDA zone, how many of the 4 types on this page live through that zone’s winter and when its freezes fall, read from the table on this page, and the freeze dates of the NOAA station nearest you.
Your answer appears here.
Full details for any ZIP code: ZIP code zone finder.
Which phlox for your zone
Penn State Extension rates garden phlox (Phlox paniculata) zones 4 to 8, and NC State Extension’s plant toolbox 4a to 8b. Penn State says its native range runs from New York west to Iowa and as far south as Georgia, Mississippi and Arkansas. Clemson’s Home & Garden Information Center says all phlox species are native to the United States.
Two close relatives grow the same way. Iowa State University Extension says spotted phlox (Phlox maculata) flowers earlier, has darker leaves and better mildew resistance, and is native to Iowa; Clemson says it is best suited to the Piedmont and mountains and is intolerant of drought. Clemson says Carolina phlox (Phlox carolina), native throughout the Southeast, grows throughout South Carolina, is heat tolerant and blooms earlier than garden phlox.
Mildew-resistant cultivars
Powdery mildew is the thing that decides how garden phlox looks. Clemson calls it by far the worst and most common disease of phlox, and says many garden phlox cultivars are the most prone to it, so cultivar selection is very important. Iowa State says selecting resistant cultivars is one of the best ways to reduce it.
The sources name the same handful. Iowa State lists ‘Jeana’ (the 2024 Perennial Plant of the Year), ‘David’, ‘Delta Snow’, ‘Lavelle’, ‘John Fanick’, ‘Peppermint Twist’ and ‘Frosted Elegance’ among those with good resistance. Clemson calls ‘David’ and ‘Robert Poore’ the two most mildew-resistant cultivars, and says ‘Delta Snow’ has done particularly well in Georgia trials and ‘John Fanick’ is very drought and heat tolerant. Penn State names ‘David’ and ‘Jeana’.
Region matters. Iowa State says a variety with good resistance in the Midwest may be susceptible elsewhere, and Clemson that conditions in the Southeast strongly favor the disease, so it is best to choose cultivars recommended by reliable southeastern sources.
Planting, thinning and staking
University of Minnesota Extension says garden phlox grows best in full sun but tolerates light shade, and that shade decreases bloom while increasing disease. It sets the crown about an inch and a half below the soil surface, works generous organic matter into the soil, spaces plants 18 inches apart, and avoids sites next to fences or walls where air circulates poorly. Clemson says at least 6 hours of sun gives the best flowering, with some afternoon shade helping in summer heat.
Minnesota buys bare-root plants in spring and avoids buying them in fall, because fall-planted phlox is more subject to frost heaving; potted plants can go in through early autumn. It mulches fall-planted phlox with 4 to 6 inches of hay, straw, chopped leaves or pine needles as soon as the soil freezes.
Thin the stems for air. Minnesota keeps five or six stems per plant once they are about six inches tall and pinches their tips, which it says gives sturdier stems, larger flower clusters and less powdery mildew; Clemson thins to 4 to 5 strong stems in spring. NC State says taller stems may need staking, and Illinois that garden phlox may require it.
Water the soil, not the leaves. Clemson says never to use overhead irrigation from sprinklers or hand watering, but to water at the base of the plants; Minnesota says the same and, if you must water overhead, to do it early in the morning. NC State says phlox needs water in dry summers and mulch to keep the root zone cool.
Supplies
Supplies the sources mention
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- Plant stakesNC State says taller garden phlox stems may need staking, and Illinois that garden phlox may require it.
- Soaker hosesClemson says never to water phlox from overhead sprinklers, but at the base of the plants, to keep the foliage drier.
- Straw mulchIowa State mulches late-summer divisions with 4 to 6 inches of straw in November so freezing and thawing do not heave them.
Dividing garden phlox
The sources agree it needs dividing and differ on how often: Minnesota every two to four years if growing well, Clemson at least every 3 years to prevent overcrowding, and Illinois says phlox needs frequent division to stay vigorous. Iowa State also divides overcrowded plantings to improve air circulation against mildew.
On timing and size they differ too. Minnesota divides in spring before new growth begins, into divisions of three to five vigorous shoots with roots, replanted with the crowns an inch or so below the surface. Iowa State divides in spring just as new growth appears or from mid-August through September, into divisions of at least 2 or 3 shoots, and mulches late-summer divisions in November with 4 to 6 inches of straw or pine needles to keep them from heaving. Clemson propagates by division or root cuttings in fall.
Deadheading and fall cleanup
Minnesota and NC State remove faded flower clusters, which prolongs bloom and stops self-seeding; Minnesota says seedlings will not resemble the parent and usually turn out pale magenta.
In fall the sources say cut it down, unlike many perennials, because of mildew. Clemson cuts plants to 2 inches above ground after the first fall frost and removes old stems and fallen leaves. NC State says plants should be cut to the ground in winter and removed from the garden to reduce powdery mildew the next season, and Iowa State that cutting off and removing diseased plant debris in fall reduces the disease.
Common problems
NC State says garden phlox has numerous pest and disease problems and is not always easy to grow well: phlox bugs, powdery mildew and root rot can be serious, and spider mites can be a problem in hot, dry weather. Minnesota calls spider mites the most troublesome pest of phlox, worse in hot, dry summers, and says other fungal leaf spots are rarely serious. Clemson says spider mites mostly occur in hot, dry conditions.
For powdery mildew, Iowa State says it is most common in shady sites and crowded plantings with poor air circulation, and that cool nights followed by warm days favor it. Move phlox growing in shade to a sunny site, Iowa State says, and divide crowded clumps. Clemson removes affected or fallen leaves early and says a fungicide may become necessary if the disease keeps spreading.
Common mistakes
- Buying a mildew-prone cultivar. Clemson and Iowa State both say cultivar choice is the best defense.
- Watering over the leaves. Clemson and Minnesota water at the base of the plants.
- Crowding the stems. Minnesota keeps five or six stems and Clemson 4 to 5.
- Planting bare-root phlox in fall. Minnesota says fall-planted phlox is more subject to frost heaving.
- Leaving diseased stems over winter. Clemson, NC State and Iowa State cut them down and remove them.
We found no Texas, Florida, Louisiana or Alabama source for garden phlox that we could read; Texas A&M AgriLife, LSU AgCenter and Alabama Extension did not load from here. Southern advice on this page comes from South Carolina and North Carolina, and Clemson draws on Georgia trials.
Questions
- Which garden phlox resists powdery mildew?
- Iowa State lists ‘Jeana’, ‘David’, ‘Delta Snow’, ‘Lavelle’ and ‘John Fanick’ among others; Clemson calls ‘David’ and ‘Robert Poore’ the two most resistant. Iowa State says resistance can differ by region.
- Should you cut back garden phlox in the fall?
- Yes. Clemson cuts plants to 2 inches above ground after the first fall frost and removes old stems and leaves; NC State cuts them to the ground and removes them to reduce powdery mildew the next season.
- How often should you divide garden phlox?
- Minnesota says every two to four years, and Clemson at least every 3 years. Minnesota divides in spring before growth begins; Iowa State in spring or from mid-August through September.
- How deep do you plant garden phlox?
- Minnesota sets the crown about an inch and a half below the soil surface for potted and bare-root plants, and replants divisions with the crowns an inch or so below the surface.
Sources
Freeze dates on this page are NOAA 1991–2020 Climate Normals, for every station the ZIP codes in each zone cite. Zones are the USDA Plant Hardiness Zone Map, 2023. The type table is a judgement, as labelled above. Growing advice is quoted from the extension publications below, each written for its own area.
- University of Minnesota Extension, Growing tall garden phlox . Written for: Minnesota (USDA zones 3a–5a).
- Iowa State University Extension and Outreach, Growing Phlox in Iowa (Last reviewed July 2022). Written for: Iowa (USDA zones 4b–6a).
- Iowa State University Extension and Outreach, How can I control powdery mildew on my garden phlox? (Updated July 10, 2025). Written for: Iowa (USDA zones 4b–6a).
- Penn State Extension, Phlox in the Home Garden , by Joan Jubela (Updated March 20, 2024). Written for: Pennsylvania (USDA zones 5b–8a).
- University of Illinois Extension, Garden Phlox . Written for: Illinois (USDA zones 5a–7a).
- Clemson Cooperative Extension, Home & Garden Information Center, Phlox (HGIC 1181) , by Karen Russ (Published May 1, 2009). Written for: South Carolina (USDA zones 8a–9b).
- NC State Extension Gardener Plant Toolbox, Phlox paniculata (garden phlox) . Written for: North Carolina (USDA zones 6b–9a).
Published October 26, 2026
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