When to plant lettuce in Denver

Where are you growing?

Comfortable

Not realistic in greenhouse

Comfortable in a cold frame

Lettuce in Denver is a good fit outdoors. The suitable growing window of 92 days covers the 40–70 days this plant usually needs.

When to plantMarch 10 – June 9

Harvest: April 19 – June 9
Season vs crop: 92 grow days vs 40–70 needed
Typical frost (last spring – first fall): April 21 – September 8

Lettuce in Denver is a good fit outdoors. The suitable growing window of 92 days covers the 40–70 days this plant usually needs.

Planting conditions

Direct sow
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 row92

Days to harvest40–70 days from seed

Mar 10 – Jun 9

Direct sow

Apr 19 – Jun 9

Harvest

Activity	Window	Notes
Direct sow	Mar 10 – Jun 9	Plant outdoors in this window.
Harvest	Apr 19 – Jun 9	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 (59 – 70 °F) and tolerable (39 – 81 °F) 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 frostApril 21

Safer last spring frostApril 21

Typical first fall frostSeptember 8

Safer first fall frostSeptember 8

Frost-free days139

Outdoor sow dateMarch 10

Direct sow windowMarch 10 – June 9

Suitable growing windowMarch 10 – June 9 (92 days)

Expected harvestApril 19 – June 9

How these dates are judged

Ideal conditions: Daytime air from 59 – 70 °F.
Suitable conditions: Daytime air from 39 – 81 °F.
Last frost and first frost: Typical spring and fall frost dates for Denver, shown in the key dates.
Days to harvest: 40–70 days from seed, 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 Lettuce: Mar 10 – Jun 9 (92 days)

Planting window for Lettuce: Mar 10 – Jun 9 (92 days)

Usually too cold: Jan 1 – Mar 8; Oct 19 – 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.

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 11 · Mar 9 – Mar 15

Average 24 to 50 °F · Possible −10 to 65 °F

Growing: too cold (inside window)

Planting: suitable

A week is in range when its average low and high sit inside the tolerance band 39 to 81 °F; it is suitable when that average range also overlaps the ideal 59 to 70 °F band and possible readings stay within 39 °F to 81 °F. Crossing a possible limit, or missing the ideal band, makes it tolerable; a possible low below 39 °F 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 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 Lettuce 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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