Yes — Strong Match
cosmos is grown as an annual, so season length decides it here, not a winter zone — and District of Columbia's typical season runs ~254 frost-free days against the ~50 cosmos needs.
Sow by about Sep 15
Cosmos is grown as an annual, so what decides it here is season length, not a winter zone. It needs about 50 frost-free days and a typical District Of Columbia season runs ~254 frost-free days, leaving 204 days of slack. That is room to sow as late as about Sep 15 and still finish before the usual first freeze (Nov 24), or to run a second succession.
Want more weeks at either end of that window? How to buy the weeks →
50 frost-free days required against District of Columbia’s ~254-day season. NOAA Regional Climate Centers ACIS 1991-2020 (28°F killing freeze), state median across counties, via stateClimateData.ts.
Your yard isn't the whole zone.
Cosmos 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 cosmos against your land's actual frost dates, sun, and soil.
We read public map data for this spot — soil, climate, flood, and parcel records. How we handle your address.
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Zone Comparison
Cosmos Needs
- USDA Zones: Data pending
- Frost-Free Days: 50+
- Sun: Full Sun
- Mature size: 4 ft tall
- Picking window: ~120 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
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 Cosmos 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
Those dates are when cosmos goes out, not when it starts. It is sown under cover about 4 weeks ahead, so counting back from District of Columbia's late-side last freeze of Mar 15 is what fixes your sowing date — and a yard that clears frost earlier than the state's late date starts earlier still.
Days to maturity vs. the window
At 70 days to maturity (USDA PLANTS Database), counting from the last hard freeze it ripens with 184 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
Frost-free days
Cosmos wants 50+ 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
Cosmos needs ~900 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
Cosmos likes near-neutral soil (pH 6-7). That's the common-ground band across District of Columbia's urban fill and silt loam — a soil test confirms it for your site. 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.
Your land, not the state average
District Of Columbia's soils run mostly silt loam, but SSURGO maps the series, texture, and drainage under your exact parcel. What matters for cosmos is the horizon its roots actually work, not the surface. That map unit, not the state average, decides how cosmos performs.
Check your parcel → Source: USDA NRCS SSURGO.
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.
Cosmos in District of Columbia — Quick Answer
- Verdict: Yes — Strong Match
- Plant Zones: Data pending (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: 70 days
What Else to Consider for Cosmos 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
Growing cosmos here specifically
Cosmos needs pH 6.0–7.0; District Of Columbia's dominant silt loam soils may or may not deliver that, so your parcel's SSURGO map unit is the real test.
Start with a soil test on your own ground and adjust pH and texture to fit cosmos's 6.0–7.0 range. How to handle it →
What to actually do about these — and the constraints that apply to every District of Columbia grower, not just cosmos — is covered on the District of Columbia growing guide.
Pollinator + Wildlife Value
Cosmos draws honeybees, native bees, and butterflies (high value, Growable Ground Plant Database). Planting it near vegetable beds can lift fruit set on neighboring crops. Outdoors, cosmos 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.
Recommended Cosmos Varieties for District of Columbia
District of Columbia publishes no state variety trial for cosmos, so we won't invent a "best for District of Columbia" list. Choose types rated to your USDA hardiness zone (7b-8a), and confirm winter survival and drainage against your own parcel.
District of Columbia Cooperative Extension
For District of Columbia-specific cultivar recommendations, planting calendars, and pest pressure for cosmos, 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 Cosmos native to District of Columbia?
No — the USDA PLANTS Database lists Cosmos 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 Cosmos in District of Columbia
When can I plant Cosmos 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 Cosmos mature before first frost in District of Columbia?
Yes — Cosmos matures in 70 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 184 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 Cosmos grown in across District of Columbia?
District of Columbia spans USDA hardiness zones 7b-8a (USDA ARS PHZM 2023). Cosmos carries a range of zones Data pending, 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). Cosmos needs 50+ frost-free days, so check whether your local microclimate runs above or below the state average before settling on a planting date.
Is Cosmos native to District of Columbia?
No — the USDA PLANTS Database lists Cosmos 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 Cosmos in District of Columbia?
Cosmos prefers pH 6-7 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 Cosmos actually grow on my specific land in District of Columbia?
State-level zone + climate data is a sketch. A Growable Ground parcel report scores cosmos 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 cosmos against your parcel's exact soil, sun, drainage, and frost data — not zone averages.
Three things about your lot that District of Columbia cosmos averages can't show:
We read public map data around District of Columbia — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the District of Columbia cosmos average
Explore More
Growing guides for cosmos
Analysis by the Growable Ground research team, grounded in USDA PLANTS, USDA NRCS SSURGO, NOAA Climate Normals (1991-2020), and named Cooperative Extension sources. How we know →
Cite this dataset
Kirchick, M. (2026). Growable Ground Plant Database [Data set]. Zenodo. https://doi.org/10.5281/zenodo.21435643
Licensed CC BY-NC 4.0. DOI 10.5281/zenodo.21435643
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