Yes — Strong Match
annual phlox (zones 2-11) covers every zone District of Columbia contains (7b-8a), so hardiness is not what limits it anywhere in the state.
Your yard isn't the whole zone.
Annual Phlox is grown as an annual, so your winter zone isn't the deciding factor — your frost-free window is. A typical District of Columbia site runs ~254 frost-free days, but that is a state median, not your yard: slope, trees, and low spots move the last-frost date across a single parcel. Enter your address and we'll score annual phlox against your land's actual frost dates, sun, and soil.
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Zone Comparison
Annual Phlox Needs
- USDA Zones: 2-11
- Frost-Free Days: 60+
- Sun: Full Sun
- Mature size: 1 ft tall
- Picking window: ~60 days of harvest
- Drought tolerance: Medium
District of Columbia Has
- USDA Zones: 7b-8a
- Last Hard Freeze (28°F): Mar 15
- First Hard Freeze (28°F): Nov 24
- Annual Rainfall: 39-43 inches
- Common Soils: Urban fill, Silt loam, Clay loam
Plant Zone Range (zones 2-11)
Preferred Soil pH
Plant data: USDA PLANTS Database / Growable Ground plant catalog. State data: USDA ARS PHZM 2023, NOAA Climate Normals, NRCS SSURGO.
When to Plant Annual Phlox in District of Columbia
The frost window
Across District of Columbia, the last spring hard freeze (28°F) clears between Mar 15 and Mar 15, and the first fall hard freeze lands between Nov 24 and Nov 24 (NOAA Regional Climate Centers ACIS, 1991-2020). Counting from the latest last freeze to the earliest first freeze, that's a 254-day window you can count on — up to 254 days on a mild site in a kind year. That marks the hard freeze, not the last light frost, so tender transplants usually wait another 2-3 weeks.
When to start the seed
Annual Phlox is direct-sown where it grows rather than started under cover, so there is no seed-tray head start to bank — District of Columbia's dates above are the whole calendar for it. That makes the last-freeze date the binding constraint, and a warmer pocket of your own yard is worth more to this crop than it is to a transplanted one.
Days to maturity vs. the window
At 60 days to maturity (USDA PLANTS Database), counting from the last hard freeze it ripens with 194 days to spare even in District of Columbia's tightest freeze scenario — room for a later start or a second sowing.
Frost window: NOAA Climate Normals 1991-2020. Plant timing fields: USDA PLANTS Database. Your site's own frost dates can run earlier or later than the state range — a parcel report pins them down.
Growing Season Fit
The zone check says annual phlox survives winter here. Whether the season is long enough — and warm enough — is a different question.
Frost-free days
Annual Phlox wants 60+ frost-free days; a typical District of Columbia site sees ~254 (NOAA Regional Climate Centers ACIS, 1991-2020). That leaves comfortable headroom for succession planting.
Growing degree days
Annual Phlox needs ~1000 GDD (base 50°F) to ripen. The state median runs ~4070 GDD (from PRISM 1991-2020 climate normals), so District of Columbia's typical season clears that easily.
GDD and chill-hour figures are computed from PRISM 1991-2020 monthly climate normals; frost-free days from NOAA Regional Climate Centers ACIS, 1991-2020. Each is the state median across its counties (P25/P75 span the within-state spread). Hardiness-zone range is USDA PHZM 2023.
Soil + Drainage Fit
Annual Phlox likes near-neutral soil (pH 5.5-7.5). That's the common-ground band across District of Columbia's urban fill and silt loam — a soil test confirms it for your site. It will grow across that whole span, but it does best between pH 6 and 6.5 — worth knowing before you decide whether a District of Columbia soil test result is a problem or just a number. Drainage matters: this plant wants well (dry spells). If your District of Columbia site is heavier clay or sits in a low spot, raised beds or amendment with compost solve it.
Plant pH and drainage requirements from USDA PLANTS Database. District of Columbia soil profile from USDA NRCS SSURGO. Site-specific verification: a 30-minute soil test from your local Extension lab.
Annual Phlox in District of Columbia — Quick Answer
- Verdict: Yes — Strong Match
- Plant Zones: 2-11 (USDA PLANTS Database)
- State Zones: 7b-8a (USDA ARS PHZM 2023)
- Growing Season: 28°F hard freezes about Mar 15 to Nov 24 (NOAA Regional Climate Centers ACIS, 1991-2020)
- Days to Maturity: 60 days
What Else to Consider for Annual Phlox in District of Columbia
Zone compatibility tells you about winter cold survival — but District of Columbia growers also need to think about:
Dense urban siting means small lots, compacted fill soils, and limited sun
Summer heat and humidity promote fungal diseases
The urban heat-island effect pushes summer temperatures above surrounding suburbs
What to actually do about these — and the constraints that apply to every District of Columbia grower, not just annual phlox — is covered on the District of Columbia growing guide.
Where in District of Columbia Fits Best
Even within District of Columbia's zones 7b-8a, county microclimates differ enough to change what thrives. These counties carry the closest zone match for annual phlox (USDA PHZM 2023):
Pollinator + Wildlife Value
Annual Phlox draws native bees, butterflies, hummingbirds, and moths (high value, Growable Ground Plant Database). Planting it near vegetable beds can lift fruit set on neighboring crops. Outdoors, annual phlox can only work that bloom inside District of Columbia's frost window — roughly 254 days, opening after the last 28°F freeze (Mar 15) and closing at the first (Nov 24), per NOAA Regional Climate Centers ACIS, 1991-2020.
District of Columbia Cooperative Extension
For District of Columbia-specific cultivar recommendations, planting calendars, and pest pressure for annual phlox, the canonical source is UDC Center for Urban Agriculture. Their fact sheets carry the local trial data we can't generalize across 50 states.
Is Annual Phlox native to District of Columbia?
No — the USDA PLANTS Database lists Annual Phlox as introduced rather than native in the Lower 48, so it is not part of District of Columbia's native flora. It grows here as a garden plant; pairing it with a few District of Columbia natives keeps local pollinators fed too.
Looking for plants that belong here? The District of Columbia growing guide lists USDA-documented natives for the state.
Native-range data: USDA PLANTS Database state-distribution records, accessed 2026-07-01.
Common Questions About Growing Annual Phlox in District of Columbia
When can I plant Annual Phlox in District of Columbia?
District of Columbia's last spring hard freeze (28°F) clears between Mar 15 and Mar 15, and the first fall hard freeze lands between Nov 24 and Nov 24 (NOAA Regional Climate Centers ACIS, 1991-2020). Time outdoor planting to after the last hard freeze for your specific site — a further two to three weeks for anything tender — and count back from those dates for transplant scheduling.
Can Annual Phlox mature before first frost in District of Columbia?
Yes — Annual Phlox matures in 60 days (USDA PLANTS Database), and District of Columbia's dependable hard-freeze-free window runs 254 days (NOAA Regional Climate Centers ACIS, 1991-2020), leaving 194 days of margin. Plant once the last hard freeze has passed — two to three weeks later for anything tender — and it ripens ahead of the first fall freeze.
What hardiness zone is Annual Phlox grown in across District of Columbia?
District of Columbia spans USDA hardiness zones 7b-8a (USDA ARS PHZM 2023). Annual Phlox carries a range of zones 2-11, so the overlap zones are where outdoor growing is most reliable.
How many frost-free days does a typical District of Columbia site have?
A typical District of Columbia site sees ~254 frost-free days per year (derived from NOAA Regional Climate Centers ACIS, 1991-2020). Annual Phlox needs 60+ frost-free days, so check whether your local microclimate runs above or below the state average before settling on a planting date.
Is Annual Phlox native to District of Columbia?
No — the USDA PLANTS Database lists Annual Phlox as introduced rather than native in the Lower 48, so it is not part of District of Columbia's native flora. It grows here as a garden plant; pairing it with a few District of Columbia natives keeps local pollinators fed too.
How should I amend the soil for Annual Phlox in District of Columbia?
Annual Phlox prefers pH 5.5-7.5 and well (dry spells) drainage (Growable Ground Plant Database). That sits in the common-ground band across District of Columbia soils — a 30-minute soil test from a local Extension lab confirms it for your specific site.
Will Annual Phlox actually grow on my specific land in District of Columbia?
State-level zone + climate data is a sketch. A Growable Ground parcel report scores annual phlox against your address's exact soil pH, drainage, sun, and frost-date data drawn from USDA SSURGO, NOAA, and PRISM — not state averages.
Check your specific parcel in District of Columbia
State-level data is a sketch. Your Growable Ground report scores annual phlox against your parcel's exact soil, sun, drainage, and frost data — not zone averages.
Three things about your lot that District of Columbia annual phlox averages can't show:
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Growing guides for annual phlox
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