Yes — Strong Match
annual phlox (zones 2-11) covers every zone Maryland contains (5b-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 Maryland site runs ~238 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
Maryland Has
- USDA Zones: 5b-8a
- Last Hard Freeze (28°F): Mar 18 - Mar 29
- First Hard Freeze (28°F): Nov 11 - Nov 27
- Annual Rainfall: 36-48 inches
- Common Soils: Silt loam, Clay, Sandy loam (Eastern Shore)
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 Maryland
The frost window
Across Maryland, the last spring hard freeze (28°F) clears between Mar 18 and Mar 29, and the first fall hard freeze lands between Nov 11 and Nov 27 (NOAA Regional Climate Centers ACIS, 1991-2020). Counting from the latest last freeze to the earliest first freeze, that's a 227-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 — Maryland'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 167 days to spare even in Maryland's tightest freeze scenario — room for a later start or a second sowing.
Timing tuned to sub-state frost dates — Garrett County, not the statewide average.
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 Maryland site sees ~238 (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 ~3789 GDD (from PRISM 1991-2020 climate normals), so Maryland'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 Maryland's silt loam and clay — 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 Maryland soil test result is a problem or just a number. Drainage matters: this plant wants well (dry spells). If your Maryland site is heavier clay or sits in a low spot, raised beds or amendment with compost solve it.
Your land, not the state average
Maryland's soils run mostly silt loam, but SSURGO maps the series, texture, and drainage under your exact parcel. What matters for annual phlox is the horizon its roots actually work, not the surface. That map unit, not the state average, decides how annual phlox performs.
Check your parcel → Source: USDA NRCS SSURGO.
Plant pH and drainage requirements from USDA PLANTS Database. Maryland soil profile from USDA NRCS SSURGO. Site-specific verification: a 30-minute soil test from your local Extension lab.
Annual Phlox in Maryland — Quick Answer
- Verdict: Yes — Strong Match
- Plant Zones: 2-11 (USDA PLANTS Database)
- State Zones: 5b-8a (USDA ARS PHZM 2023)
- Growing Season: 28°F hard freezes about Mar 18 - Mar 29 to Nov 11 - Nov 27 (NOAA Regional Climate Centers ACIS, 1991-2020)
- Days to Maturity: 60 days
What Else to Consider for Annual Phlox in Maryland
Zone compatibility tells you about winter cold survival — but Maryland growers also need to think about:
Heavy Piedmont clay drains poorly
Humidity and heat in summer promote disease
Deer pressure in suburban areas is extreme
Growing annual phlox here specifically
Maryland's soils run mostly silt loam (Ultisols), and whether that suits annual phlox's pH 5.5–7.5 preference comes down to your exact parcel, not the statewide picture.
Pull your parcel's SSURGO map unit, test pH, and amend toward annual phlox's 5.5–7.5 target before planting. How to handle it →
What to actually do about these — and the constraints that apply to every Maryland grower, not just annual phlox — is covered on the Maryland growing guide.
Timing shifts within Maryland
Maryland isn't one climate. In Garrett County, the last hard freeze (28°F) holds until about Apr 22 — roughly 29 days later than the recorded state median — so plant annual phlox to your county's window, not the statewide date.
Annual Phlox needs about 60 days of frost-free season to complete its cycle. Even Garrett County — Maryland’s shortest season at 190 frost-free days — clears that by 130 days, so season length isn’t the constraint anywhere in Maryland. What varies is your own parcel.
Across Maryland’s 24 counties the frost-free season runs from 190 days in Garrett County to 270 days in Talbot County — a spread of 80 days, which is why a single statewide planting date misleads. The median Maryland county sees 238 frost-free days, leaving annual phlox about 178 days of slack on a typical parcel — room for a second sowing where the season runs long.
County last-freeze dates and frost-free day counts: NOAA Regional Climate Centers ACIS (1991-2020), county 28°F freeze (earlier than the folk 32°F "last frost"). Annual Phlox's 60-day requirement: USDA PLANTS / Growable Ground plant database (minimum frost-free days). A parcel report resolves your address's own frost dates.
Where in Maryland Fits Best
Even within Maryland's zones 5b-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 Maryland's frost window — roughly 238 days, opening after the last 28°F freeze (Mar 18 - Mar 29) and closing at the first (Nov 11 - Nov 27), per NOAA Regional Climate Centers ACIS, 1991-2020.
Recommended Annual Phlox Varieties for Maryland
Maryland publishes no state variety trial for annual phlox, so we won't invent a "best for Maryland" list. Choose types rated to your USDA hardiness zone (5b-8a), and confirm winter survival and drainage against your own parcel.
Maryland Cooperative Extension
For Maryland-specific cultivar recommendations, planting calendars, and pest pressure for annual phlox, the canonical source is University of Maryland Extension. Their fact sheets carry the local trial data we can't generalize across 50 states.
Is Annual Phlox native to Maryland?
No — the USDA PLANTS Database lists Annual Phlox as introduced rather than native in the Lower 48, so it is not part of Maryland's native flora. It grows here as a garden plant; pairing it with a few Maryland natives keeps local pollinators fed too.
Looking for plants that belong here? The Maryland 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 Maryland
When can I plant Annual Phlox in Maryland?
Maryland's last spring hard freeze (28°F) clears between Mar 18 and Mar 29, and the first fall hard freeze lands between Nov 11 and Nov 27 (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 Maryland?
Yes — Annual Phlox matures in 60 days (USDA PLANTS Database), and Maryland's dependable hard-freeze-free window runs 227 days (NOAA Regional Climate Centers ACIS, 1991-2020), leaving 167 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 Maryland?
Maryland spans USDA hardiness zones 5b-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 Maryland site have?
A typical Maryland site sees ~238 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. In cooler counties like Garrett, the freeze-free season runs shorter than the state average, so verify your own county's window.
Is Annual Phlox native to Maryland?
No — the USDA PLANTS Database lists Annual Phlox as introduced rather than native in the Lower 48, so it is not part of Maryland's native flora. It grows here as a garden plant; pairing it with a few Maryland natives keeps local pollinators fed too.
How should I amend the soil for Annual Phlox in Maryland?
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 Maryland 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 Maryland?
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 Maryland
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 Maryland annual phlox averages can't show:
We read public map data around Maryland — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Maryland annual phlox average
Explore More
Growing guides for annual phlox
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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