When to plant sweet corn in Denver

In Denver, typical last spring frost is May 8 and typical first fall frost is October 13. Typical last spring frost: May 8. Sweet corn in Denver is a good fit outdoors. The suitable growing window of 99 days covers the 60–90 days this plant usually needs.

Sweet corn

How to grow Sweet corn Denver climate Weekly temperatures and windows

Where are you growing?

Comfortable

Comfortable in a cold frame

Sweet corn in Denver is a good fit outdoors. The suitable growing window of 99 days covers the 60–90 days this plant usually needs.

When to plantMay 23 – June 15

Harvest: July 22 – September 25
Season vs crop: 99 grow days vs 60–90 needed
Typical frost (last spring – first fall): May 8 – October 13

Sweet corn in Denver is a good fit outdoors. The suitable growing window of 99 days covers the 60–90 days this plant usually needs.

Planting conditions

Direct sow
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 row99

Days to harvest60–90 days from seed

May 23 – Jun 15

Direct sow

Jun 16 – Jul 21

Grow outdoors

Jul 22 – Sep 25

Harvest

Activity	Window	Notes
Direct sow	May 23 – Jun 15	Plant outdoors in this window.
Grow outdoors	Jun 16 – Jul 21	Plants grow outdoors until harvest.
Harvest	Jul 22 – Sep 25	Expected harvest from typical days to harvest.

Direct sow
Grow outdoors
Harvest

Blue fill is usually too cold for this plant. Dashed lines are typical last and first frost (35 seasons (1991–2025)). 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 (21 – 32 °C70 – 90 °F21 – 32 °C (70 – 90 °F)) and tolerable (13 – 35 °C55 – 95 °F13 – 35 °C (55 – 95 °F)) ranges.

Ideal / plantable
Tolerable
Too cold
Too hot
Outside window

Planting uses sow / plant-out rules; growing shows daytime air against this plant’s ideal and tolerable ranges.

Key dates

Typical last spring frostMay 8

Low-risk last spring frostMay 19

Typical first fall frostOctober 13

Low-risk first fall frostSeptember 25

Frost-free days157

Outdoor sow dateMay 23

Direct sow windowMay 23 – June 15

Suitable growing windowMay 23 – August 29 (99 days)

Expected harvestJuly 22 – September 25

Sow again for a steady harvest

Sow quick crops like radish and lettuce every 1–2 weeks, and slower ones like beans and carrots every 2–3 weeks. Stop when there is not enough time left before your first autumn frost for the crop to mature.

In Denver, sow sweet corn every 10 days from May 23 to about June 12. That is about 3 sowings in a typical year — a short row or a few square feet each time. Shorter autumn days slow growth, so we allow two extra weeks before the season end.

Sow outdoors
Grow outdoors
Harvest

Each row is one succession sowing. Dashed lines are typical last and first frost.

Succession sowing dates for Sweet corn in Denver
Sowing	Sow outdoors	Harvest
1	May 23	July 22 – August 5
2	June 2	August 1 – August 15
3	June 12	August 11 – August 25

These dates are deliberately cautious. They come out earlier than common rules like '8 weeks before first frost', because we use the low-risk frost date, leave time for picking and add two weeks for shorter autumn days.

How these dates are judged

Ideal conditions: Daytime air from 21 – 32 °C70 – 90 °F21 – 32 °C (70 – 90 °F).
Suitable conditions: Daytime air from 13 – 35 °C55 – 95 °F13 – 35 °C (55 – 95 °F).
Last frost and first frost: Typical spring and fall frost dates for Denver, shown in the key dates.
Days to harvest: 60–90 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. Air ratings on the weekly chart colour only weeks inside that same window — see weekly temperatures and windows.

Other plants for Denver

Calculated by Plan & Plant. Method. Data 35 seasons (1991–2025).

Frost and suitability dates are typical figures from climate statistics.

Based on 35 years (1991–2025) of ERA5-Land data from Open-Meteo, for an area of about 10 km. Typical dates, not a guarantee.

Dates for Denver use ERA5-Land cell 39.70, -105.00. How we calculated this · Algorithm 2026-10-season-10.

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