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When to plant tomato in Denver

How to grow TomatoDenver climate
Where are you growing?

Tight fit

Not realistic in greenhouse

Tomato in Denver is doable with planning outdoors. 87 suitable days are enough for fast varieties (55 days) but not slow ones (90 days).

Start indoors
April 2 – April 19
Transplant outside
June 1 – June 18
Harvest
July 26 – August 26
Season vs crop
87 grow days vs 55–90 needed
Typical frost (last spring – first fall)
April 21 – September 8

Tomato in Denver is doable with planning outdoors. 87 suitable days are enough for fast varieties (55 days) but not slow ones (90 days).

Start seeds indoors April 2 – April 19, then transplant June 1 – June 18 so the crop can finish outdoors.

Planting conditions

Tomato planting activities across the year: Start indoors, Grow indoors, Harden off, Transplant outside, Grow outdoors, HarvestJFMAMJJASOND~Apr 21~Sep 8
  • Start indoors
  • Grow 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 row87
Days to harvest55–90 days from transplant
Apr 2 – Apr 19
Start indoors
Apr 20 – May 24
Grow indoors
May 25 – May 31
Harden off
June 1
Transplant outside
Jun 2 – Jul 25
Grow outdoors
Jul 26 – Aug 26
Harvest
ActivityWindowNotes
Start indoorsApr 2 – Apr 19Sow indoors before the outdoor window.
Grow indoorsApr 20 – May 24Seedlings grow indoors until harden or transplant.
Harden offMay 25 – May 31Acclimate seedlings outdoors before planting.
Transplant outsideJune 1Move plants outside on this day (start of the plant-out window).
Grow outdoorsJun 2 – Jul 25Plants grow outdoors until harvest.
HarvestJul 26 – Aug 26Expected 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 (70 – 84 °F) and tolerable (55 – 95 °F) ranges.

Tomato planting and growing weeks in DenverJANFEBMARAPRMAYJUNJULAUGSEPOCTNOVDECPlantingGrowing
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 frostApril 21
Safer last spring frostApril 21
Typical first fall frostSeptember 8
Safer first fall frostSeptember 8
Frost-free days139
Earliest indoor seed startApril 2
Latest indoor seed startApril 19
Transplant outdoorsJune 1 – June 18
Direct sow windownot recommended here
Suitable growing windowJune 1 – August 26 (87 days)
Expected harvestJuly 26 – August 26

How these dates are judged

Ideal conditions
Daytime air from 70 – 84 °F.
Suitable conditions
Daytime air from 55 – 95 °F.
Last frost and first frost
Typical spring and fall frost dates for Denver, shown in the key dates.
Days to harvest
55–90 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 Tomato: Jun 1 – Aug 26 (87 days)

Planting window for Tomato: Jun 1 – Jun 18 (18 days)

Usually too cold: Jan 1 – May 31; Sep 7 – Dec 31

Outdoors: weekly temperatures and windows

Temperatures across the year for Denver. 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−40 °C−40 °F−30 °C−22 °F−20 °C−4 °F−10 °C14 °F0 °C32 °F10 °C50 °F20 °C68 °F30 °C86 °F40 °C104 °FTolerable 13–35 °CTolerable 55–95 °FIdeal 21–29 °CIdeal 70–84 °FWindowGrowingJun 1 – Aug 26PlantingJun 1 – Jun 18Last frost ~Apr 21First frost ~Sep 8
  • 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 23 · Jun 1 – Jun 7

Average 51 to 77 °F · Possible 38 to 91 °F

Growing: too cold (inside window)

Planting: suitable

A week is in range when its average low and high sit inside the tolerance band 55 to 95 °F; it is suitable when that average range also overlaps the ideal 70 to 84 °F band and possible readings stay within 32 °F to 95 °F. Crossing a possible limit, or missing the ideal band, makes it tolerable; any chance of frost (possible low below 32 °F) makes it too cold. 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 Denver

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 39.70, -105.00, 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 Tomato from frost dates, temperature ratings, and crop timing rules.
  • Confidence: Provisional — short or thin sample for this place.
  • Full methodology (algorithm 2026-10-season-6).

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