Yes — Strong Match
hyssop (zones 3-9) covers every zone Delaware contains (7a-8a), so hardiness is not what limits it anywhere in the state.
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 hyssop against your parcel's actual hardiness, soil, and sun.
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Zone Comparison
Hyssop Needs
- USDA Zones: 3-9
- Frost-Free Days: 180+
- Sun: Part Sun
- Mature size: 2 ft tall
- Picking window: ~90 days of harvest
- 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 3-9)
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 Hyssop 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.
When to start the seed
Those dates are when hyssop goes out, not when it starts. It is sown under cover about 8 weeks ahead, so counting back from Delaware's late-side last freeze of Mar 23 is what fixes your sowing date — and a yard that clears frost earlier than the state's late date starts earlier still.
Establishment timing
As a long-lived plant, hyssop isn't racing the calendar to a harvest date. Plant it in spring once the last hard-freeze window passes so roots settle in through the full season, or in early fall while the soil still holds summer warmth.
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 hyssop survives winter here. Whether the season is long enough — and warm enough — is a different question.
Frost-free days
Hyssop 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.
Growing degree days
Hyssop needs ~900 GDD (base 50°F) to ripen. The state median runs ~3732 GDD (from PRISM 1991-2020 climate normals), so Delaware'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
Hyssop tolerates a wide pH range (pH 5.5-8.5) — 3 units, acid ground through alkaline — so soil acidity is rarely what limits it in Delaware. A soil test is still worth having, but for what else it tells you about this site, not to clear this plant. It will grow across that whole span, but it does best between pH 6 and 7.5 — 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), excessive (dry/moderately dry). If your Delaware 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. Delaware soil profile from USDA NRCS SSURGO. Site-specific verification: a 30-minute soil test from your local Extension lab.
Hyssop in Delaware — Quick Answer
- Verdict: Yes — Strong Match
- Plant Zones: 3-9 (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)
- Days to Maturity: 85 days
What Else to Consider for Hyssop 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
What to actually do about these — and the constraints that apply to every Delaware grower, not just hyssop — is covered on the Delaware growing guide.
Timing shifts within Delaware
Hyssop 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"). Hyssop's 180-day requirement: USDA PLANTS / Growable Ground plant database (minimum frost-free days). A parcel report resolves your address's own frost dates.
Where in Delaware Fits Best
Even within Delaware's zones 7a-8a, county microclimates differ enough to change what thrives. These counties carry the closest zone match for hyssop (USDA PHZM 2023):
Pollinator + Wildlife Value
Hyssop 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, hyssop 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.
Delaware Cooperative Extension
For Delaware-specific cultivar recommendations, planting calendars, and pest pressure for hyssop, 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 Hyssop native to Delaware?
No — the USDA PLANTS Database lists Hyssop 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 Hyssop in Delaware
When can I plant Hyssop 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). Hyssop is a long-lived planting, so target spring just after your local last hard freeze — or early fall while the soil holds warmth — and let it establish through the season.
What hardiness zone is Hyssop grown in across Delaware?
Delaware spans USDA hardiness zones 7a-8a (USDA ARS PHZM 2023). Hyssop carries a range of zones 3-9, 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). Hyssop 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 Hyssop native to Delaware?
No — the USDA PLANTS Database lists Hyssop 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 Hyssop in Delaware?
Hyssop tolerates pH 5.5-8.5 and well (dry spells), excessive (dry/moderately dry) drainage (FAO ECOCROP). That is a 3-unit span, acid ground through alkaline, so pH is rarely what limits this plant on a Delaware site — amend for drainage and organic matter first.
Will Hyssop actually grow on my specific land in Delaware?
State-level zone + climate data is a sketch. A Growable Ground parcel report scores hyssop 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 hyssop against your parcel's exact soil, sun, drainage, and frost data — not zone averages.
Three things about your lot that Delaware hyssop averages can't show:
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