Portsmouth frost dates and planting season

Name: Portsmouth
Address: England, United Kingdom

When to plant vegetables here. Cover calendars (fleece, cold frame, unheated greenhouse) are on each plant’s when-to-plant page.

Portsmouth has a long growing season, with roughly 262 frost-free days between the typical frost dates. Typical last spring frost: around March 9 (half of years later). Typical first fall frost: around November 27. Plant cool-season crops after about January 26; wait until about May 25 for warm-season crops.

Frost-free days262Mar 9 – Nov 27

Frost-free season in Portsmouth. Based on average frost dates. Adjust a week or two for your conditions.

Cover calendars (fleece, cold frame, unheated greenhouse) live on each crop’s when-to-plant page.

Weekly possible temperature−4 – 31 °C

Frost-free days262

Typical last spring frostMarch 9

Typical first fall frostNovember 27

Days suitable for warm-season vegetables161 (May 25 – November 1)

Days suitable for cool-season vegetables344 (All year except a short gap (January 4 – January 26))

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.

Frost dates calculated by Plan & Plant from Weather data by Open-Meteo.com (CC BY 4.0). Local frost pockets, valleys and coastal sites can differ by 1–3 weeks.

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.
Confidence: Provisional — short or thin sample for this place.
Full methodology (algorithm 2026-10-season-5).

Report a problem

What to plant when

Cool-season vegetables

Earliest outdoor start: January 26

Suitable window: All year except a short gap (January 4 – January 26)

Cool-season crops prefer cooler weather.

See cool-season details

Warm-season vegetables

Earliest outdoor start: May 25

Suitable window: May 25 – November 1

Warm-season crops need mild or warm weather and cannot take frost.

Frost kills these crops, and cold snaps set them back.

See warm-season details

Green = usually good weeks to grow; blue or gray = usually too cold for that crop type.

Starter plants for Portsmouth

Cool-season

Radish Sow: February 25 – November 21 Planting dates
Arugula Sow: February 25 – November 8 Planting dates
Spinach Sow: February 25 – November 1 Planting dates
Lettuce Sow: February 25 – October 27 Planting dates
Kale Sow: February 25 – April 21 Planting dates
Beet Sow: March 11 – August 29 Planting dates

Warm-season

Zucchini Sow: June 10 – August 4 Planting dates
Cucumber Sow: June 10 – August 4 Planting dates
Green bean Sow: June 1 – August 13 Planting dates
Tomato Transplant: May 24 – July 15 Start indoors, then transplant. Planting dates
Bell pepper Transplant: June 10 – July 10 Start indoors, then transplant. Planting dates

How these dates are judged

Last frost: The typical last spring date when frost is still expected.
First frost: The typical first fall date when frost returns.
Frost-free days: The approximate days between those two dates.
Cool-season vegetables: Crops that prefer cooler weather, such as lettuce, kale, peas, and radish.
Warm-season vegetables: Crops that need warm weather and cannot take frost, such as tomato, pepper, squash, and beans.

Cool-season planting window

Jan 26 – Jan 4 (344 days)

Warm-season planting window

May 25 – Nov 1 (161 days)

Usually too cold

January 5 – January 25

Weekly temperatures and planting windows

Temperatures across the year for Portsmouth, with cool- and warm-season weeks and frost dates.

Possible min to max
Average min to max
Suitable
Tolerable
Too cold
Too hot

Selected week · tap a week or use the arrows

Week 5 · Jan 26 – Feb 1

Average 4 to 9 °C · Possible 0 to 12 °C

Cool season: suitable

Warm season: too cold

A week is suitable for a crop type when its average low and high sit inside that type's range and its possible readings stay within the frost and heat limits (cool: −2 °C to 27 °C, warm: 0 °C to 32 °C); crossing a limit makes it tolerable, and for warm crops any chance of frost makes it too cold.

Based on average frost dates.

England, United Kingdom · 50.79899, -1.09125 · 2026

Coldest weekly possible temperature−4 °C

Hottest weekly possible temperature31 °C

Last expected spring frostMarch 9

First expected fall frostNovember 27

Show all 53 weeks