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When to plant hardneck garlic in Portsmouth

How to grow Hardneck garlicPortsmouth climate
Where are you growing?

Comfortable

Hardneck garlic in Portsmouth is a good fit outdoors. Planted in autumn, harvested next summer (about 7–9 months).

When to plantOctober 2 – November 12

Harvest
210–270 days from planting
Season vs crop
312 grow days vs 210–270 needed
Typical frost (last spring – first fall)
March 9 – November 27

Hardneck garlic in Portsmouth is a good fit outdoors. Planted in autumn, harvested next summer (about 7–9 months).

Planting conditions

Hardneck garlic planting activities across the year: Direct sowJFMAMJJASOND~Mar 9~Nov 27
  • Direct sow
Local activity windows for this place and growing method. Dashed lines are typical last and first frost.
Suitable growing days in a row312
Days to harvest210–270 days from planting
Oct 2 – Nov 12
Direct sow
ActivityWindowNotes
Direct sowOct 2 – Nov 12Plant outdoors in this window.
Based on average frost dates. Adjust a week or two for your conditions.

Planting and growing across the year

Planting is the sow / plant-out window. Growing is daytime air versus this plant’s ideal (17 – 23 °C) and tolerable (−5 – 30 °C) ranges.

Hardneck garlic planting and growing weeks in PortsmouthJANFEBMARAPRMAYJUNJULAUGSEPOCTNOVDECPlantingGrowing
Planting uses sow / plant-out rules (frost, soil germination, night, and last-sow): green when plantable, blue diagonal when nights or soil are too cold, amber cross-hatch when too hot, faint for other calendar limits. Growing shows daytime air against this plant’s ideal and tolerable ranges across the year.

Key dates

Typical last spring frostMarch 9
Safer last spring frostApril 8
Typical first fall frostNovember 27
Safer first fall frostNovember 20
Frost-free days262
Outdoor sow dateOctober 2
Direct sow windowOctober 2 – November 12
Suitable growing windowOctober 2 – August 9 (312 days)

How these dates are judged

Ideal conditions
Daytime air from 17 – 23 °C.
Suitable conditions
Daytime air from −5 – 30 °C.
Last frost and first frost
Typical spring and fall frost dates for Portsmouth, shown in the key dates.
Days to harvest
210–270 days from planting, from typical days to harvest.
Sowing window
Dated sow and harvest bars use frost dates, soil minima, night limits, and last-sow count-back from typical crop timing. The year strip and weekly chart use the same window: air ratings only colour weeks inside it.

Growing window for Hardneck garlic: Oct 2 – Aug 9 (312 days)

Planting window for Hardneck garlic: Oct 2 – Nov 12 (42 days)

Outdoors: weekly temperatures and windows

Temperatures across the year for Portsmouth. Shaded bands are this plant’s ideal and tolerable daytime air ranges. Growing is daytime air suitability; Planting is sow / plant-out conditions (same colour language). Window brackets mark each stretch.

JanFebMarAprMayJunJulAugSepOctNovDec−10 °C14 °F0 °C32 °F10 °C50 °F20 °C68 °F30 °C86 °FTolerable -5–30 °CTolerable 23–86 °FIdeal 17–23 °CIdeal 63–73 °FWindowGrowingOct 2 – Aug 9PlantingOct 2 – Nov 12Last frost ~Mar 9First frost ~Nov 27
  • Ideal range
  • Tolerable range
  • Possible min to max
  • Average min to max
  • Suitable
  • Tolerable
  • Too cold
  • Too hot

Selected week · tap a week or use the arrows

Week 1 · Jan 1 – Jan 4

Average 5 to 9 °C · Possible −1 to 14 °C

Growing: tolerable

Planting: too cold

A week is in range when its average low and high sit inside the tolerance band −5 to 30 °C; it is suitable when that average range also overlaps the ideal 17 to 23 °C band and possible readings stay within −5 °C to 30 °C. Crossing a possible limit, or missing the ideal band, makes it tolerable; a possible low below −5 °C makes it tolerable. When a sowing window is calculated, weeks outside that window are uncoloured even if air is in range.

Based on average frost dates.

Show all 53 weeks
Cover method weekly charts

Outdoor weekly chart is above. Open a cover chart only if you grow under fleece, a cold frame, or an unheated greenhouse.

Other plants for Portsmouth

Calculated by Plan & Plant · Method · Data 2019–2026

Frost and suitability dates are typical figures from climate statistics. Microclimates vary; they are not a guarantee.

How we calculated this
  • Data: ERA5-Land via Open-Meteo, cell 50.80, -1.09, years 2019–2026 (not a 30-year climate normal yet).
  • Typical and safer dates: Typical last frost is the date after which half of winters in this sample had no more frost; safer is later in the sample so fewer winters still frosted.
  • Crop rule: Local windows for Hardneck garlic from frost dates, temperature ratings, and crop timing rules.
  • Confidence: Provisional — short or thin sample for this place.
  • Full methodology (algorithm 2026-10-season-5).

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