Yes — Strong Match
sweet alyssum (zones 5-9) covers every zone Pennsylvania contains (5b-8a), so hardiness is not what limits it anywhere in the state.
Your yard isn't the whole zone.
Pennsylvania spans zones 5b-8a, but your yard sits in exactly one — and slope, tree cover, and cold-air pockets nudge it further. Enter your address and we'll score sweet alyssum against your parcel's actual hardiness, soil, and sun.
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Zone Comparison
Sweet Alyssum Needs
- USDA Zones: 5-9
- Frost-Free Days: 40+
- Sun: Full Sun
- Mature size: 6 in tall
- Picking window: ~90 days of harvest
- Drought tolerance: Medium
Pennsylvania Has
- USDA Zones: 5b-8a
- Last Hard Freeze (28°F): Apr 6 - Apr 24
- First Hard Freeze (28°F): Oct 25 - Nov 3
- Annual Rainfall: 36-48 inches
- Common Soils: Silt loam, Shale-derived, Limestone-derived
Plant Zone Range (zones 5-9)
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 Sweet Alyssum in Pennsylvania
The frost window
Across Pennsylvania, the last spring hard freeze (28°F) clears between Apr 6 and Apr 24, and the first fall hard freeze lands between Oct 25 and Nov 3 (NOAA Regional Climate Centers ACIS, 1991-2020). Counting from the latest last freeze to the earliest first freeze, that's a 184-day window you can count on — up to 211 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 sweet alyssum goes out, not when it starts. It is sown under cover about 4 weeks ahead, so counting back from Pennsylvania's late-side last freeze of Apr 24 is what fixes your sowing date — and a yard that clears frost earlier than the state's late date starts earlier still.
Winter standing
Pennsylvania runs as cold as USDA zone 5, and no sourced winter-hardiness floor is on record for sweet alyssum, so this page does not state whether it overwinters here — and gives no fall establishment date on the strength of a guess. Whether sweet alyssum is a permanent planting or a replant-every-spring crop for you turns on your own zone within Pennsylvania; check its hardiness range against that before treating it as long-lived ground.
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 sweet alyssum survives winter here. Whether the season is long enough — and warm enough — is a different question.
Frost-free days
Sweet Alyssum wants 40+ frost-free days; a typical Pennsylvania site sees ~197 (NOAA Regional Climate Centers ACIS, 1991-2020). That leaves comfortable headroom for succession planting.
Growing degree days
Sweet Alyssum needs ~600 GDD (base 50°F) to ripen. The state median runs ~2447 GDD (from PRISM 1991-2020 climate normals), so Pennsylvania'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
Sweet Alyssum likes near-neutral soil (pH 6-7). That's the common-ground band across Pennsylvania's silt loam and shale-derived — a soil test confirms it for your site. Drainage matters: this plant wants well (dry spells). If your Pennsylvania 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. Pennsylvania soil profile from USDA NRCS SSURGO. Site-specific verification: a 30-minute soil test from your local Extension lab.
Sweet Alyssum in Pennsylvania — Quick Answer
- Verdict: Yes — Strong Match
- Plant Zones: 5-9 (USDA PLANTS Database)
- State Zones: 5b-8a (USDA ARS PHZM 2023)
- Growing Season: 28°F hard freezes about Apr 6 - Apr 24 to Oct 25 - Nov 3 (NOAA Regional Climate Centers ACIS, 1991-2020)
- Days to Maturity: 55 days
What Else to Consider for Sweet Alyssum in Pennsylvania
Zone compatibility tells you about winter cold survival — but Pennsylvania growers also need to think about:
Rocky shale soils in the ridge-and-valley region
Short mountain seasons in the Poconos and Alleghenies
Deer pressure is among the highest in the US
What to actually do about these — and the constraints that apply to every Pennsylvania grower, not just sweet alyssum — is covered on the Pennsylvania growing guide.
Timing shifts within Pennsylvania
Sweet Alyssum needs about 40 days of frost-free season to complete its cycle. Even Potter County — Pennsylvania’s shortest season at 160 frost-free days — clears that by 120 days, so season length isn’t the constraint anywhere in Pennsylvania. What varies is your own parcel.
Across Pennsylvania’s 67 counties the frost-free season runs from 160 days in Potter County to 250 days in Philadelphia County — a spread of 90 days, which is why a single statewide planting date misleads. The median Pennsylvania county sees 197 frost-free days, leaving sweet alyssum about 157 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"). Sweet Alyssum's 40-day requirement: USDA PLANTS / Growable Ground plant database (minimum frost-free days). A parcel report resolves your address's own frost dates.
Where in Pennsylvania Fits Best
Even within Pennsylvania's zones 5b-8a, county microclimates differ enough to change what thrives. These counties carry the closest zone match for sweet alyssum (USDA PHZM 2023):
Pollinator + Wildlife Value
Sweet Alyssum 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, sweet alyssum can only work that bloom inside Pennsylvania's frost window — roughly 197 days, opening after the last 28°F freeze (Apr 6 - Apr 24) and closing at the first (Oct 25 - Nov 3), per NOAA Regional Climate Centers ACIS, 1991-2020.
Pennsylvania Cooperative Extension
For Pennsylvania-specific cultivar recommendations, planting calendars, and pest pressure for sweet alyssum, the canonical source is Penn State Extension. Their fact sheets carry the local trial data we can't generalize across 50 states.
Is Sweet Alyssum native to Pennsylvania?
No — the USDA PLANTS Database lists Sweet Alyssum as introduced rather than native in the Lower 48, so it is not part of Pennsylvania's native flora. It grows here as a garden plant; pairing it with a few Pennsylvania natives keeps local pollinators fed too.
Looking for plants that belong here? The Pennsylvania 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 Sweet Alyssum in Pennsylvania
When can I plant Sweet Alyssum in Pennsylvania?
Pennsylvania's last spring hard freeze (28°F) clears between Apr 6 and Apr 24, and the first fall hard freeze lands between Oct 25 and Nov 3 (NOAA Regional Climate Centers ACIS, 1991-2020). No sourced winter-hardiness floor is on record for Sweet Alyssum, so this page does not state whether it overwinters in Pennsylvania and publishes no fall establishment date for it — check its hardiness range against your own zone before treating it as a permanent planting.
What hardiness zone is Sweet Alyssum grown in across Pennsylvania?
Pennsylvania spans USDA hardiness zones 5b-8a (USDA ARS PHZM 2023). Sweet Alyssum carries a range of zones 5-9, so the overlap zones are where outdoor growing is most reliable.
How many frost-free days does a typical Pennsylvania site have?
A typical Pennsylvania site sees ~197 frost-free days per year (derived from NOAA Regional Climate Centers ACIS, 1991-2020). Sweet Alyssum needs 40+ frost-free days, so check whether your local microclimate runs above or below the state average before settling on a planting date.
Is Sweet Alyssum native to Pennsylvania?
No — the USDA PLANTS Database lists Sweet Alyssum as introduced rather than native in the Lower 48, so it is not part of Pennsylvania's native flora. It grows here as a garden plant; pairing it with a few Pennsylvania natives keeps local pollinators fed too.
How should I amend the soil for Sweet Alyssum in Pennsylvania?
Sweet Alyssum prefers pH 6-7 and well (dry spells) drainage (Growable Ground Plant Database). That sits in the common-ground band across Pennsylvania soils — a 30-minute soil test from a local Extension lab confirms it for your specific site.
Will Sweet Alyssum actually grow on my specific land in Pennsylvania?
State-level zone + climate data is a sketch. A Growable Ground parcel report scores sweet alyssum 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 Pennsylvania
State-level data is a sketch. Your Growable Ground report scores sweet alyssum against your parcel's exact soil, sun, drainage, and frost data — not zone averages.
Three things about your lot that Pennsylvania sweet alyssum averages can't show:
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