Generally — Most Areas
delphinium (zones 3-7) suits most of District of Columbia (7b-8a) — zone 7 are in range, and the rest of the state is the exception.
Delphinium in District of Columbia — the short answer
Delphinium in District of Columbia: hardy in zones 3–7, against a state median of ~254 frost-free days.
- Plant zones
- 3-7
- Manual horticultural correction (source not retained); NC State Extension and Missouri Botanical Garden, with the remaining rows from other published sources or Growable Ground compilation
- District of Columbia zones
- 7b-8a
- USDA PHZM 2023
- Frost window
- Mar 15 – Nov 24
- NOAA RCC ACIS 1991-2020, 28°F
- Typical season
- ~254 days
- NOAA Regional Climate Centers ACIS, 1991-2020
Plant data: Growable Ground Plant Database, compiled from FAO ECOCROP, USDA PLANTS and university Extension sources — per-field provenance varies and is published with the dataset.
Your yard isn't the whole zone.
District of Columbia spans zones 7b-8a, but your yard has its own microclimate — slope, trees, and low spots shift frost and sun across a single parcel. Enter your address and we'll score delphinium against your land's actual soil, sun, and frost.
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Where Delphinium Stands in District of Columbia
Delphinium is rated for zones 3–7 — a cold floor USDA puts at -40 to -30°F. No District of Columbia county sits inside it, so in open ground this is a grown-under-cover plant here rather than a bed plant — which is a statement about District of Columbia winters, not about delphinium.
Above the zone 7 ceiling
1 county
- District of Columbia County · zone 8a
Too little winter chill rather than too much cold — a low-chill selection is what changes it.
County hardiness zones: USDA Plant Hardiness Zone Map (PHZM) 2023, per county. A zone is a 10°F band of average annual extreme minimum temperature, so the floor above is the band the plant's rating denotes, not a single measured kill point. Slope, shelter and cold-air drainage routinely move a site half a zone either way from its county figure — which is the part only your address resolves.
Zone Comparison
Delphinium Needs
- USDA Zones: 3-7
- Mature size: 5 ft tall
- Picking window: ~30 days of harvest
- Drought tolerance: Low
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 3-7)
Plant data: Growable Ground Plant Database, compiled from FAO ECOCROP, USDA PLANTS, and university Extension sources — per-field provenance varies and is published with the dataset. State data: USDA ARS PHZM 2023, NOAA Climate Normals, NRCS SSURGO.
When to Plant Delphinium 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 delphinium goes out, not when it starts. It is sown under cover about 8 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.
Frost window: NOAA Climate Normals 1991-2020. Plant timing fields: Growable Ground Plant Database — frost-free days from FAO ECOCROP, days to harvest from university Extension production guides, and growing-degree-day and chill-hour minimums that are compilation estimates rather than published figures. Your site's own frost dates can run earlier or later than the state range — a parcel report pins them down.
What Else to Consider for Delphinium 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 delphinium — is covered on the District of Columbia growing guide.
Pollinator + Wildlife Value
Delphinium draws native bees, butterflies, and hummingbirds (moderate value, Growable Ground Plant Database). Planting it near vegetable beds can lift fruit set on neighboring crops. Outdoors, delphinium 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 delphinium, 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 Delphinium native to District of Columbia?
No — the USDA PLANTS Database lists Delphinium 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 Delphinium in District of Columbia
When can I plant Delphinium 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.
What hardiness zone is Delphinium grown in across District of Columbia?
District of Columbia spans USDA hardiness zones 7b-8a (USDA ARS PHZM 2023). Delphinium carries a range of zones 3-7, 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). Delphinium should be matched against that window, so check whether your local microclimate runs above or below the state average before settling on a planting date.
Is Delphinium native to District of Columbia?
No — the USDA PLANTS Database lists Delphinium 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.
Will Delphinium actually grow on my specific land in District of Columbia?
State-level zone + climate data is a sketch. A Growable Ground parcel report scores delphinium 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 delphinium against your parcel's exact soil, sun, drainage, and frost data — not zone averages.
Three things about your lot that District of Columbia delphinium 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 delphinium average
Explore More
Growing guides for delphinium
Explore District of Columbia county by county
District of Columbia carries 1 counties with their own USDA zone — a sample of the growing pages for delphinium there:
Where else delphinium grows
Delphinium's zone band crosses state lines — these are the states closest to District of Columbia in winter climate where it also has a page, plus the far ends of its range. Each one re-answers the question with that state's own record.
More to grow in District of Columbia
District of Columbia has a growing page for 1,013 plants — a rotating sample of the rest of the shelf.
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