Generally — Most Areas
sweetspire (zones 5-11) suits most of Alaska (1a-9a) — zones 5-9 are in range, and the rest of the state is the exception.
Sweetspire in Alaska — the short answer
Sweetspire in Alaska: hardy in zones 5–11, shade.
- Plant zones
- 5-11
- Rated hardy to zone 5a by NC State Extension Gardener Plant Toolbox; USDA PLANTS Database lists -24 °F, converted to zone 5a, checked Oct 2026. Ceiling: our plant database.
- Alaska zones
- 1a-9a
- USDA PHZM 2023
- Frost window
- Apr 16 - May 15 – Sep 24 - Oct 29
- NOAA RCC ACIS 1991-2020, 28°F
- Shortest county season
- 85 days
- NOAA Regional Climate Centers ACIS station record, 1991-2020, county 28°F killing freeze
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.
Alaska spans zones 1a-9a, 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 sweetspire against your parcel's actual hardiness, soil, and sun.
We read public map data for this spot — soil, climate, flood, and parcel records. How we handle your address.
No card required · your parcel report in seconds — read in full free for your first 14 days
Alaska is not one climate
Alaska’s winter-low ladder runs across 30 counties, from zone 1 in Yukon-Koyukuk County to zone 7.5 in Chugach County. That is 65°F between the two counties’ average coldest night — the difference between sweetspire overwintering in the ground and coming under cover.
The middle half of 30 counties runs 2.5–5 zones, with a median of 4 zones — a 6.5-zone span end to end.
Measured across 30 Alaska counties. USDA PHZM 2023, per county. Quartiles are order statistics — every figure shown is a value a real county recorded, not an interpolation. Your own site sits somewhere inside this range; a parcel report resolves where.
Where in Alaska Fits Best
Sweetspire is rated for zones 5–11 — a cold floor USDA puts at -20 to -10°F. Against Alaska’s 30 counties that band holds in 8 of them, and the line runs at Petersburg County (zone 5a-8a), the coldest county still inside it.
Inside zones 5–11
8 counties
- Aleutians East County · zone 5b-8a
- Ketchikan Gateway County · zone 5b-8a
- Wrangell County · zone 5b-8a
3 of 8 shown
Below the zone 5 floor
22 counties
- Yukon-Koyukuk County · zone 1a-4a
- North Slope County · zone 1b-4a
- Northwest Arctic County · zone 1b-4a
3 of 22 shown
Winter cold is the limit here — the same plant works in a container that comes under cover.
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.
Even within Alaska's zones 1a-9a, county microclimates differ enough to change what thrives. These counties carry the closest zone match for sweetspire (USDA PHZM 2023):
Zone Comparison
Sweetspire Needs
- USDA Zones: 5-11
- Sun: Shade
- Mature size: 6 ft tall
- Drought tolerance: Low
Alaska Has
- USDA Zones: 1a-9a
- Last Hard Freeze (28°F): Apr 16 - May 15
- First Hard Freeze (28°F): Sep 24 - Oct 29
- Annual Rainfall: 10-160 inches
- Common Soils: Permafrost, Glacial silt, Volcanic ash
Plant Zone Range (zones 5-11)
Preferred Soil pH
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 Sweetspire in Alaska
The frost window
Across Alaska, the last spring hard freeze (28°F) clears between Apr 16 and May 15, and the first fall hard freeze lands between Sep 24 and Oct 29 (NOAA Regional Climate Centers ACIS, 1991-2020). Counting from the latest last freeze to the earliest first freeze, that's a 132-day window you can count on — up to 196 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.
Winter standing
Alaska runs as cold as USDA zone 1, and no sourced winter-hardiness floor is on record for sweetspire, so this page does not state whether it overwinters here — and gives no fall establishment date on the strength of a guess. Whether sweetspire is a permanent planting or a replant-every-spring crop for you turns on your own zone within Alaska; check its hardiness range against that before treating it as long-lived ground.
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.
Soil + Drainage Fit
Sweetspire tolerates a wide pH range (pH 4-7.5) — 3.5 units, acid ground through alkaline — so soil acidity is rarely what limits it in Alaska. A soil test is still worth having, but for what else it tells you about this site, not to clear this plant.
Plant pH requirements: FAO ECOCROP and USDA PLANTS, with the remaining rows from other published sources or Growable Ground compilation. Drainage: FAO ECOCROP, with the remaining rows from other published sources or Growable Ground compilation. Alaska soil profile from USDA NRCS SSURGO. Site-specific verification: a 30-minute soil test from your local Extension lab.
What Else to Consider for Sweetspire in Alaska
Zone compatibility tells you about winter cold survival — but Alaska growers also need to think about:
Extremely short growing season (70-110 frost-free days)
Permafrost prevents deep root growth in many areas
Limited soil development in glacial terrain
What to actually do about these — and the constraints that apply to every Alaska grower, not just sweetspire — is covered on the Alaska growing guide.
Where in Alaska Sweetspire Is Zone-Hardy
Sweetspire is rated for USDA zones 5–11. 8 of Alaska’s 30 counties fall inside that band. The coldest that does is Petersburg County at zone 5a-8a. 10 counties sit below the plant’s zone 5 floor, where an unprotected plant is relying on snow cover and a mild year. Where you are in Alaska decides this one.
Across those 30 counties Alaska’s winter-low ladder runs from zone 1a-4a in Yukon-Koyukuk County to zone 7b in Chugach County — 6.5 USDA zones of spread, which is 65°F between the two counties’ average coldest night of the year. That is why a statewide hardiness answer is where you start and not where you finish.
The planting window moves with it. North Slope County holds its last hard freeze (28°F) until about Jun 7, while Sitka County is clear by Mar 24 — 75 days apart. Set sweetspire out on your county’s date, not the state’s.
County hardiness zones: USDA Plant Hardiness Zone Map (PHZM) 2023, per county. County last-freeze dates: NOAA Regional Climate Centers ACIS (1991-2020), county 28°F killing freeze — earlier than the folk 32°F "last frost". Sweetspire’s zone 5–11 band: Rated hardy to zone 5a by NC State Extension Gardener Plant Toolbox; USDA PLANTS Database lists -24 °F, converted to zone 5a, checked Oct 2026. Ceiling: our plant database.. A parcel report resolves your address’s own zone and frost dates rather than its county’s.
Pollinator + Wildlife Value
Sweetspire draws honeybees, native bees, and butterflies (moderate value, Growable Ground Plant Database). Planting it near vegetable beds can lift fruit set on neighboring crops. Outdoors, sweetspire can only work that bloom inside Alaska's frost window — roughly 147 days, opening after the last 28°F freeze (Apr 16 - May 15) and closing at the first (Sep 24 - Oct 29), per NOAA Regional Climate Centers ACIS station record, 1991-2020.
Alaska Cooperative Extension
For Alaska-specific cultivar recommendations, planting calendars, and pest pressure for sweetspire, the canonical source is UAF Cooperative Extension Service. Their fact sheets carry the local trial data we can't generalize across 50 states.
Is Sweetspire native to Alaska?
Sweetspire is native to parts of the Lower 48, but the USDA PLANTS Database (accessed 2026-07-01) does not document a native range in Alaska. It can still earn a place in a Alaska garden — the zone comparison above tells you whether it will thrive.
Looking for plants that belong here? The Alaska 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 Sweetspire in Alaska
When can I plant Sweetspire in Alaska?
Alaska's last spring hard freeze (28°F) clears between Apr 16 and May 15, and the first fall hard freeze lands between Sep 24 and Oct 29 (NOAA Regional Climate Centers ACIS, 1991-2020). No sourced winter-hardiness floor is on record for Sweetspire, so this page does not state whether it overwinters in Alaska 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 Sweetspire grown in across Alaska?
Alaska spans USDA hardiness zones 1a-9a (USDA ARS PHZM 2023). Sweetspire carries a range of zones 5-11, so the overlap zones are where outdoor growing is most reliable.
How many frost-free days does a typical Alaska site have?
A typical Alaska site sees ~147 frost-free days per year (derived from NOAA Regional Climate Centers ACIS station record, 1991-2020). Sweetspire needs 180+ frost-free days, so check whether your local microclimate runs above or below the state average before settling on a planting date.
Is Sweetspire native to Alaska?
Sweetspire is native to parts of the Lower 48, but the USDA PLANTS Database (accessed 2026-07-01) does not document a native range in Alaska. It can still earn a place in a Alaska garden — the zone comparison above tells you whether it will thrive.
How should I amend the soil for Sweetspire in Alaska?
Sweetspire tolerates pH 4-7.5 (USDA PLANTS). That is a 3.5-unit span, acid ground through alkaline, so pH is rarely what limits this plant on a Alaska site — amend for drainage and organic matter first.
Will Sweetspire actually grow on my specific land in Alaska?
State-level zone + climate data is a sketch. A Growable Ground parcel report scores sweetspire 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 Alaska
State-level data is a sketch. Your Growable Ground report scores sweetspire against your parcel's exact soil, sun, drainage, and frost data — not zone averages.
Three things about your lot that Alaska sweetspire averages can't show:
We read public map data around Alaska — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Alaska sweetspire average
Explore More
Growing guides for sweetspire
Explore Alaska county by county
Alaska carries 30 counties with their own USDA zone — a sample of the growing pages for sweetspire there:
Where else sweetspire grows
Sweetspire's zone band crosses state lines — these are the states closest to Alaska 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 Alaska
Alaska has a growing page for 1,011 plants — a rotating sample of the rest of the shelf.
Last updated: