When to plant hardneck garlic in Denver

How to grow Hardneck garlic Denver climate

Where are you growing?

Comfortable

Hardneck garlic in Denver is a good fit outdoors. Planted in autumn, harvested next summer (about 7–9 months).

When to plantSeptember 8 – September 22

Harvest: 210–270 days from planting
Season vs crop: 285 grow days vs 210–270 needed
Typical frost (last spring – first fall): April 21 – September 8

Hardneck garlic in Denver is a good fit outdoors. Planted in autumn, harvested next summer (about 7–9 months).

Mulch with 8–10 cm of straw after the ground starts to freeze to stop the cloves heaving (UMN, Wisconsin Extension).

Planting conditions

Direct sow

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 row285

Days to harvest210–270 days from planting

Sep 8 – Sep 22

Direct sow

Activity	Window	Notes
Direct sow	Sep 8 – Sep 22	Plant outdoors in this window.

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 (63 – 73 °F) and tolerable (23 – 86 °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 dateSeptember 8

Direct sow windowSeptember 8 – September 22

Suitable growing windowSeptember 8 – June 19 (285 days)

How these dates are judged

Ideal conditions: Daytime air from 63 – 73 °F.
Suitable conditions: Daytime air from 23 – 86 °F.
Last frost and first frost: Typical spring and fall frost dates for Denver, shown in the key dates.
Days to harvest: 210–270 days from planting, 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 Hardneck garlic: Sep 8 – Jun 19 (285 days)

Planting window for Hardneck garlic: Sep 8 – Sep 22 (15 days)

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 1 · Jan 1 – Jan 4

Average 16 to 41 °F · Possible −11 to 54 °F

Growing: too cold (inside window)

Planting: too cold

A week is in range when its average low and high sit inside the tolerance band 23 to 86 °F; it is suitable when that average range also overlaps the ideal 63 to 73 °F band and possible readings stay within 23 °F to 86 °F. Crossing a possible limit, or missing the ideal band, makes it tolerable; a possible low below 23 °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 Hardneck garlic 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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