When to plant broccoli in Portsmouth

Where are you growing?

Tight fit

Tight fit in greenhouse

Comfortable in a cold frame

Broccoli in Portsmouth is a good fit outdoors. The suitable growing window of 315 days covers the 55–75 days this plant usually needs.

Start indoors: January 7 – March 3
Transplant outside: February 25 – April 21
Harvest: April 21 – July 5
Season vs crop: 315 grow days vs 55–75 needed
Typical frost (last spring – first fall): March 9 – November 27

Broccoli in Portsmouth is a good fit outdoors. The suitable growing window of 315 days covers the 55–75 days this plant usually needs.

Planting conditions

Start indoors
Harden off
Transplant outside
Grow outdoors
Harvest

Local activity windows for this place and growing method. Blue fill is usually too cold for this plant. Dashed lines are typical last and first frost.

Suitable growing days in a row315

Days to harvest55–75 days from transplant

Jan 7 – Mar 3

Start indoors

Feb 18 – Feb 24

Harden off

February 25

Transplant outside

Feb 26 – Apr 20

Grow outdoors

Apr 21 – Jul 5

Harvest

Activity	Window	Notes
Start indoors	Jan 7 – Mar 3	Sow indoors before the outdoor window.
Harden off	Feb 18 – Feb 24	Acclimate seedlings outdoors before planting.
Transplant outside	February 25	Move plants outside on this day (start of the plant-out window).
Grow outdoors	Feb 26 – Apr 20	Plants grow outdoors until harvest.
Harvest	Apr 21 – Jul 5	Expected harvest from typical days to harvest.

Blue fill is usually too cold for this plant. Dashed lines are typical last and first frost. 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 (15 – 24 °C) and tolerable (4 – 27 °C) ranges.

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

Earliest indoor seed startJanuary 7

Latest indoor seed startMarch 3

Transplant outdoorsFebruary 25 – April 21

Direct sow windownot recommended here

Suitable growing windowFebruary 25 – January 5 (315 days)

Expected harvestApril 21 – July 5

How these dates are judged

Ideal conditions: Daytime air from 15 – 24 °C.
Suitable conditions: Daytime air from 4 – 27 °C.
Last frost and first frost: Typical spring and fall frost dates for Portsmouth, shown in the key dates.
Days to harvest: 55–75 days from transplant, 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 Broccoli: Feb 25 – Jan 5 (315 days)

Planting window for Broccoli: Feb 25 – Apr 21 (56 days)

Usually too cold: Jan 5 – Jan 25

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.

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: not sowable

A week is in range when its average low and high sit inside the tolerance band 4 to 27 °C; it is suitable when that average range also overlaps the ideal 15 to 24 °C band and possible readings stay within 4 °C to 27 °C. Crossing a possible limit, or missing the ideal band, makes it tolerable; a possible low below 4 °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 Broccoli 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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