When to plant · 22 cities · zones 5b–7a
When to plant basil in Colorado
Start Genovese Basil seeds indoors around Apr 9 and transplant around May 21 — the Colorado statewide median, counted from a last spring frost of May 7 across 493 ZIP codes and 190 NOAA stations.
The rule: Basil is damaged below about 50 °F, well before frost: transplant two weeks after the last frost, not on it.
Colorado basil, by step
Statewide median last frost May 7, first fall frost Oct 6, 2027 season. Each cultivar's own indoor lead time and days to maturity, same engine as the Plan Builder.
| Cultivar | Start indoors | Plant out | First harvest | Days |
|---|---|---|---|---|
| Genovese BasilGenovese | Apr 9 | May 21 | Jul 20 | 60 from transplant |
Tight means first harvest lands within two weeks of the median first fall frost. Statewide dates are the ZIP-weighted median of every NOAA 1991–2020 station Colorado's ZIP codes resolve to; 34 of 527 ZIPs have no datable freeze and are left out.
Basil in Colorado, city by city
Genovese Basil, scheduled from each city's nearest NOAA station — the same dates as its frost page.
| City | Last frost | Start indoors | Plant out | First harvest |
|---|---|---|---|---|
| Denverzone 6a | May 4 | Apr 6 | May 18 | Jul 17 |
| Colorado Springszone 6a | May 3 | Apr 5 | May 17 | Jul 16 |
| Aurorazone 6a | May 5 | Apr 7 | May 19 | Jul 18 |
| Fort Collinszone 5b | May 3 | Apr 5 | May 17 | Jul 16 |
| Lakewoodzone 6a | May 3 | Apr 5 | May 17 | Jul 16 |
| Thorntonzone 6a | May 2 | Apr 4 | May 16 | Jul 15 |
| Arvadazone 6a | May 5 | Apr 7 | May 19 | Jul 18 |
| Westminsterzone 6a | May 2 | Apr 4 | May 16 | Jul 15 |
| Greeleyzone 5b | May 2 | Apr 4 | May 16 | Jul 15 |
| Pueblozone 6a | Apr 26 | Mar 29 | May 10 | Jul 9 |
| Centennialzone 6a | May 5 | Apr 7 | May 19 | Jul 18 |
| Boulderzone 6a | May 6 | Apr 8 | May 20 | Jul 19 |
| Longmontzone 5b | May 7 | Apr 9 | May 21 | Jul 20 |
| Castle Rockzone 5b | May 9 | Apr 11 | May 23 | Jul 22 |
| Lovelandzone 5b | May 3 | Apr 5 | May 17 | Jul 16 |
| Broomfieldzone 6a | May 2 | Apr 4 | May 16 | Jul 15 |
| Grand Junctionzone 7a | Apr 28 | Mar 31 | May 12 | Jul 11 |
| Commerce Cityzone 6a | May 3 | Apr 5 | May 17 | Jul 16 |
| Parkerzone 5b | May 9 | Apr 11 | May 23 | Jul 22 |
| Littletonzone 6a | May 2 | Apr 4 | May 16 | Jul 15 |
| Brightonzone 5b | May 3 | Apr 5 | May 17 | Jul 16 |
| Windsorzone 5b | May 3 | Apr 5 | May 17 | Jul 16 |
What these basil become
What Colorado basil need
Genovese Sweet Basil Seed
The large-leaf, low-anise Italian basil that pesto is defined by. Thai and lemon basils are good plants and wrong ingredients.
Organic Seed Starter Potting MixMust have
Seed-starting mix is not potting soil with a nicer label — it is finer, lighter, and low in nutrients on purpose, because a seedling's first roots want air and moisture, not fertiliser.
T8 Full-Spectrum Grow Lights, 1 ft 4-packMust have
A south window in March delivers a fraction of the light a pepper seedling needs, and the plant tells you by stretching. Two inches of LED above the canopy for 16 hours a day fixes it permanently.
5-Gallon Fabric Grow Bags, 5-Pack
Fabric pots air-prune roots and drain faster than a plastic pot can, which is the entire reason container tomatoes fail. Five gallons is the honest minimum for a pepper; a tomato wants ten.
Ocean Forest Potting SoilMust have
Pre-charged with enough nutrition to carry a transplant for its first month without feeding, which is exactly the window when most container plants stall.
6" Micro-Tip Pruning SnipsMust have
Ninety percent of sauce-garden cutting is snipping a pepper stem or a basil node, and a fine-tipped snip does it better than any pruner. Pulling peppers by hand tears the branch.
Mesh Strainers, Stainless, 3-Count
The last pass before bottling. A fine mesh catches the skin fragments and seed shards that make a hot sauce gritty and clog a woozy bottle's dripper insert.
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Basil in Colorado: questions
When should I plant basil in Colorado?
Transplant around May 21 at the statewide median; across the state that date runs from May 14 in the warmest tenth of Colorado's ZIP codes to Jun 20 in the coldest. To cut the freeze risk to one year in ten, count from May 21 instead of the median last frost. Use the city table for your own town.
When do I start basil seeds indoors in Colorado?
Around Apr 9 for Genovese Basil: 4 weeks before the statewide median last frost, on soil held at 70–80 °F.
When is the last frost in Colorado?
The ZIP-weighted median of NOAA 1991–2020 station medians is May 7. In the warmest tenth of Colorado's ZIP codes the median last frost falls on or before Apr 30; in the coldest tenth, on or after Jun 6.
When will Colorado basil be ready to harvest?
Genovese Basil planted on the statewide date is ready around Jul 20: 60 days from transplant.
More for Colorado
- When to plant tomatoes
- When to plant peppers
- When to plant tomatillos
- When to plant onions
- When to plant cilantro
- When to plant carrots
- When to plant mustard greens
Basil in every state → · Colorado frost dates → · How frost-date math works →