Unlikely — Zone Mismatch
Sydney blue gum (zones 9-11) does not overlap with Delaware's zone range (7a-8a). Growing outdoors is unlikely without significant protection.
One zone short — what would close it
Sydney Blue Gum is hardy to zone 9, and the warmest ground in Delaware is zone 8 — 1 zone short. Planted in open ground it will not survive a Delaware winter. To grow it here, grow sydney blue gum in a container and move it under cover for the coldest weeks, or give it a greenhouse.
Season extension and overwintering under cover both work at this margin. How to buy the weeks →
Zone math from 9-11 (plant) against 7-8 (Delaware). Lift modeled by crop_engine Sprint 20B effective_zone_modifier (+2 zones) via api/fast_sections.py Unlock Engine v2.
Your yard isn't the whole zone.
Delaware spans zones 7a-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 sydney blue gum 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.
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Zone Comparison
Sydney Blue Gum Needs
- USDA Zones: 9-11
- Frost-Free Days: 180+
- Sun: Full Sun
- Drought tolerance: Medium
Delaware Has
- USDA Zones: 7a-8a
- Last Hard Freeze (28°F): Mar 23 - Mar 23
- First Hard Freeze (28°F): Nov 17 - Nov 19
- Annual Rainfall: 42-48 inches
- Common Soils: Sandy loam, Silt loam, Tidal marsh
Plant Zone Range (zones 9-11)
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 Sydney Blue Gum in Delaware
The frost window
Across Delaware, the last spring hard freeze (28°F) clears between Mar 23 and Mar 23, and the first fall hard freeze lands between Nov 17 and Nov 19 (NOAA Regional Climate Centers ACIS, 1991-2020). Counting from the latest last freeze to the earliest first freeze, that's a 239-day window you can count on — up to 241 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
Delaware runs as cold as USDA zone 7, and no sourced winter-hardiness floor is on record for sydney blue gum, so this page does not state whether it overwinters here — and gives no fall establishment date on the strength of a guess. Whether sydney blue gum is a permanent planting or a replant-every-spring crop for you turns on your own zone within Delaware; 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 sydney blue gum does not survive a Delaware winter in the ground. The season figures below measure a different question — whether it could finish a season here at all — and they only bear on Delaware under protection.
Frost-free days
Sydney Blue Gum wants 180+ frost-free days; a typical Delaware site sees ~241 (NOAA Regional Climate Centers ACIS, 1991-2020). That leaves comfortable headroom for succession planting.
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
Sydney Blue Gum likes near-neutral soil (pH 5-7.5). That's the common-ground band across Delaware's sandy loam and silt loam — a soil test confirms it for your site. It will grow across that whole span, but it does best between pH 5.5 and 6.5 — worth knowing before you decide whether a Delaware soil test result is a problem or just a number. Drainage matters: this plant wants well (dry spells). If your Delaware site is heavier clay or sits in a low spot, raised beds or amendment with compost solve it.
Your land, not the state average
SSURGO maps about 19.8% of Delaware as poorly or somewhat-poorly drained, and the class flips parcel to parcel. Sydney Blue Gum sits mid-range for drought tolerance, so either extreme can cost you — your soil map unit, not the state average, is the real answer.
Check your parcel → Source: USDA NRCS SSURGO.
Plant pH and drainage requirements from USDA PLANTS Database. Delaware soil profile from USDA NRCS SSURGO. Site-specific verification: a 30-minute soil test from your local Extension lab.
Sydney Blue Gum in Delaware — Quick Answer
- Verdict: Unlikely — Zone Mismatch
- Plant Zones: 9-11 (USDA PLANTS Database)
- State Zones: 7a-8a (USDA ARS PHZM 2023)
- Growing Season: 28°F hard freezes about Mar 23 - Mar 23 to Nov 17 - Nov 19 (NOAA Regional Climate Centers ACIS, 1991-2020)
What Else to Consider for Sydney Blue Gum in Delaware
Zone compatibility tells you about winter cold survival — but Delaware growers also need to think about:
Sandy soils in southern DE drain too quickly
Salt spray damage near the coast
Rising water tables in low-lying areas
Growing sydney blue gum here specifically
Sydney Blue Gum roots run deep and prefer pH 5.0–7.5, but drainage comes first here: SSURGO maps about 19.8% of Delaware as poorly or somewhat-poorly drained, and wet ground rots its crown before pH ever matters.
Plant sydney blue gum on a raised, gravel-amended berm so water drains fast and the crown stays dry. How to handle it →
What to actually do about these — and the constraints that apply to every Delaware grower, not just sydney blue gum — is covered on the Delaware growing guide.
Timing shifts within Delaware
Sydney Blue Gum needs about 180 days of frost-free season to complete its cycle. Even Sussex County — Delaware’s shortest season at 238 frost-free days — clears that by 58 days, so season length isn’t the constraint anywhere in Delaware. What varies is your own parcel.
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"). Sydney Blue Gum's 180-day requirement: USDA PLANTS / Growable Ground plant database (minimum frost-free days). A parcel report resolves your address's own frost dates.
Pollinator + Wildlife Value
Sydney Blue Gum draws honeybees and native bees (high value, Growable Ground Plant Database). Planting it near vegetable beds can lift fruit set on neighboring crops. Outdoors, sydney blue gum can only work that bloom inside Delaware's frost window — roughly 241 days, opening after the last 28°F freeze (Mar 23 - Mar 23) and closing at the first (Nov 17 - Nov 19), per NOAA Regional Climate Centers ACIS, 1991-2020.
Good to Know Before You Plant Sydney Blue Gum
Sydney Blue Gum is listed as toxic to dogs, cats (leaves) at a moderate level (ASPCA). Most listed plants only cause brief upset — a raised bed or a fenced corner usually keeps curious pets clear.
Delaware Cooperative Extension
For Delaware-specific cultivar recommendations, planting calendars, and pest pressure for sydney blue gum, the canonical source is University of Delaware Cooperative Extension. Their fact sheets carry the local trial data we can't generalize across 50 states.
Is Sydney Blue Gum native to Delaware?
No — the USDA PLANTS Database lists Sydney Blue Gum as introduced rather than native in the Lower 48, so it is not part of Delaware's native flora. It grows here as a garden plant; pairing it with a few Delaware natives keeps local pollinators fed too.
Looking for plants that belong here? The Delaware 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 Sydney Blue Gum in Delaware
When can I plant Sydney Blue Gum in Delaware?
Delaware's last spring hard freeze (28°F) clears between Mar 23 and Mar 23, and the first fall hard freeze lands between Nov 17 and Nov 19 (NOAA Regional Climate Centers ACIS, 1991-2020). No sourced winter-hardiness floor is on record for Sydney Blue Gum, so this page does not state whether it overwinters in Delaware 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 Sydney Blue Gum grown in across Delaware?
Delaware spans USDA hardiness zones 7a-8a (USDA ARS PHZM 2023). Sydney Blue Gum carries a range of zones 9-11, so the overlap zones are where outdoor growing is most reliable.
How many frost-free days does a typical Delaware site have?
A typical Delaware site sees ~241 frost-free days per year (derived from NOAA Regional Climate Centers ACIS, 1991-2020). Sydney Blue Gum 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 Sydney Blue Gum native to Delaware?
No — the USDA PLANTS Database lists Sydney Blue Gum as introduced rather than native in the Lower 48, so it is not part of Delaware's native flora. It grows here as a garden plant; pairing it with a few Delaware natives keeps local pollinators fed too.
How should I amend the soil for Sydney Blue Gum in Delaware?
Sydney Blue Gum prefers pH 5-7.5 and well (dry spells) drainage (FAO ECOCROP). That sits in the common-ground band across Delaware soils — a 30-minute soil test from a local Extension lab confirms it for your specific site.
Will Sydney Blue Gum actually grow on my specific land in Delaware?
State-level zone + climate data is a sketch. A Growable Ground parcel report scores sydney blue gum 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 Delaware
State-level data is a sketch. Your Growable Ground report scores sydney blue gum against your parcel's exact soil, sun, drainage, and frost data — not zone averages.
Three things about your lot that Delaware sydney blue gum averages can't show:
We read public map data around Delaware — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Delaware sydney blue gum average
Explore More
Growing guides for sydney blue gum
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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