Boulder, CO Vegetable Planting Calendar

What to plant now in Boulder

In October:

• Plant garlic cloves (Oct 1–14)

The list above is for the month this page was built; the box is refreshed in your browser for today's date.

Spring planting dates

“Plant out” means transplanting for crops started indoors and sowing or planting directly in the garden for the others. Each column applies CSU Extension's timing rule to a different last-frost anchor: aggressive = typical date (May 6, 50% risk), balanced = May 11 (30%), safe = May 18 (10%). For hardy crops the cell shows the CSU “as early as” window.

Before sowing, check the soil too. CSU recommends taking its temperature at 4 inches (6 inches for beans). Since NOAA publishes no soil-temperature normals, we give CSU's minimum soil temperature for each crop rather than a date.

Fall planting dates

Latest dates for a fall harvest, using the University of Nebraska–Lincoln Extension count-back formula: days to harvest (CSU) + 14-day fall factor + 14-day frost-tender factor for frost-sensitive crops, counted back from the first-frost date. For transplanted crops (CSU days are from transplant) the result is the latest transplant date; seeds go in CSU's transplant-age weeks earlier. We add no harvest period, so these dates give you a first harvest by the first frost, not a long harvest.

Month-by-month: what to plant in Boulder

What to plant in Boulder in February

• Start broccoli seeds indoors (Feb 23 – Mar 9)
• Start cabbage seeds indoors (Feb 23 – Mar 9)

What to plant in Boulder in March

• Start cauliflower seeds indoors (Mar 9–23)
• Start eggplant seeds indoors (Mar 23 – Apr 13)
• Start pepper seeds indoors (Mar 30 – Apr 13)
• Start broccoli seeds indoors (Feb 23 – Mar 9)
• Start cabbage seeds indoors (Feb 23 – Mar 9)

What to plant in Boulder in April

• Onions (dry, from sets): plant sets outdoors (Apr 8 – May 4)
• Peas: direct sow outdoors (Apr 8 – May 4)
• Lettuce (leaf): direct sow outdoors (Apr 8 – May 4)
• Broccoli: transplant outdoors (Apr 8 – May 4)
• Cabbage: transplant outdoors (Apr 8 – May 4)
• Kohlrabi: direct sow outdoors (Apr 8 – May 4)
• Green onions: direct sow outdoors (Apr 8 – May 4)
• Radishes: direct sow outdoors (Apr 8 – May 4)
• Spinach: direct sow outdoors (Apr 8 – May 4)
• Turnips: direct sow outdoors (Apr 8 – May 4)
• Potatoes: plant (seed pieces) outdoors (Apr 22 – May 18)
• Carrots: direct sow outdoors (Apr 22 – May 18)
• Cauliflower: transplant outdoors (Apr 22 – May 18)
• Beets: direct sow outdoors (Apr 22 – May 18)
• Swiss chard: direct sow outdoors (Apr 22 – May 18)
• Parsnips: direct sow outdoors (Apr 22 – May 18)
• Start eggplant seeds indoors (Mar 23 – Apr 13)
• Start pepper seeds indoors (Mar 30 – Apr 13)

What to plant in Boulder in May

• Start tomato seeds indoors (May 2–16)
• Beans (snap): direct sow outdoors (May 6–18)
• Summer squash: direct sow outdoors (May 6–18)
• Sweet corn: direct sow outdoors (May 6–18)
• Cucumbers: direct sow outdoors (May 6–18)
• Start cabbage seeds indoors for a fall crop (May 10–24)
• Peppers: transplant outdoors (May 20 – Jun 1)
• Eggplant: transplant outdoors (May 20 – Jun 1)
• Cantaloupe: direct sow outdoors (May 20 – Jun 1)
• Watermelon: direct sow outdoors (May 20 – Jun 1)
• Winter squash: direct sow outdoors (May 20 – Jun 1)
• Start broccoli seeds indoors for a fall crop (May 30 – Jun 13)
• Onions (dry, from sets): plant sets outdoors (Apr 8 – May 4)
• Peas: direct sow outdoors (Apr 8 – May 4)
• Lettuce (leaf): direct sow outdoors (Apr 8 – May 4)
• Broccoli: transplant outdoors (Apr 8 – May 4)
• Cabbage: transplant outdoors (Apr 8 – May 4)
• Kohlrabi: direct sow outdoors (Apr 8 – May 4)
• Green onions: direct sow outdoors (Apr 8 – May 4)
• Radishes: direct sow outdoors (Apr 8 – May 4)
• Spinach: direct sow outdoors (Apr 8 – May 4)
• Turnips: direct sow outdoors (Apr 8 – May 4)
• Potatoes: plant (seed pieces) outdoors (Apr 22 – May 18)
• Carrots: direct sow outdoors (Apr 22 – May 18)
• Cauliflower: transplant outdoors (Apr 22 – May 18)
• Beets: direct sow outdoors (Apr 22 – May 18)
• Swiss chard: direct sow outdoors (Apr 22 – May 18)
• Parsnips: direct sow outdoors (Apr 22 – May 18)

What to plant in Boulder in June

• Tomatoes: transplant outdoors (Jun 20)
• Last day to set out cabbage transplants for a fall harvest (by Jun 28)
• Peppers: transplant outdoors (May 20 – Jun 1)
• Eggplant: transplant outdoors (May 20 – Jun 1)
• Cantaloupe: direct sow outdoors (May 20 – Jun 1)
• Watermelon: direct sow outdoors (May 20 – Jun 1)
• Winter squash: direct sow outdoors (May 20 – Jun 1)
• Start broccoli seeds indoors for a fall crop (May 30 – Jun 13)

What to plant in Boulder in July

• Last day to sow beans (snap) for a fall harvest (by Jul 9)
• Last day to sow carrots for a fall harvest (by Jul 13)
• Last day to sow cucumbers for a fall harvest (by Jul 14)
• Last day to sow peas for a fall harvest (by Jul 18)
• Last day to set out broccoli transplants for a fall harvest (by Jul 18)
• Last day to sow summer squash for a fall harvest (by Jul 19)
• Last day to sow lettuce (leaf) for a fall harvest (by Jul 23)
• Last day to sow green onions for a fall harvest (by Jul 23)
• Last day to sow beets for a fall harvest (by Jul 23)
• Last day to sow swiss chard for a fall harvest (by Jul 23)

What to plant in Boulder in August

• Last day to sow kohlrabi for a fall harvest (by Aug 2)
• Last day to sow turnips for a fall harvest (by Aug 2)
• Last day to sow spinach for a fall harvest (by Aug 12)
• Last day to sow radishes for a fall harvest (by Aug 22)

What to plant in Boulder in October

• Plant garlic cloves (Oct 1–14)

Crop-by-crop notes

When to plant tomatoes in Boulder

Very tender crop. Set tomatoes out about Jun 20, whichever risk level you go by. That date comes from CSU Extension's night rule (nights above 52°F): the average nightly low at Boulder first rises above 52°F on Jun 20. CSU's other rule, at least 2 weeks after the average last frost, would allow about May 20 in Boulder. Sow seeds indoors May 2–16, 5–7 weeks before transplanting on Jun 20. Fruit set suffers when nights drop below 55°F (CSU). The normal low at Boulder reaches 55°F on Jul 2. CSU's typical time from transplant to harvest for tomato plants is 65 days. Set out on Jun 20, they would start producing around Aug 24, 42 days before the typical first frost (Oct 5).

When to plant peppers in Boulder

Very tender crop. CSU Extension's rule is 2+ weeks after the average last frost, which puts peppers outside around May 20 (typical date), May 25 (balanced) or Jun 1 (safer 10% date). Start seeds indoors Mar 30 – Apr 13, 6–8 weeks ahead of transplanting on May 25. Below 55°F at night, fruit set suffers (CSU). At Boulder, the normal low reaches 55°F on Jul 2. CSU's typical time from transplant to harvest for pepper plants is 70 days. Set out on May 25, they would start producing around Aug 3, 63 days before the typical first frost (Oct 5).

When to plant potatoes in Boulder

Semi-hardy crop. Per CSU, potatoes can go in as early as 0–2 weeks before the average last frost: roughly Apr 22 – May 6 in Boulder (typical date) or May 4–18 (safer date). The soil should be at least 45°F.

When to plant onions (dry, from sets) in Boulder

Hardy crop. CSU says onions (dry, from sets) can go in as early as 2–4 weeks before the average last frost: roughly Apr 8–22 in Boulder using the typical date, or Apr 20 – May 4 using the safer one. Wait until the soil can be worked and is at least 35°F.

When to plant peas in Boulder

Hardy crop. CSU says peas can go in as early as 2–4 weeks before the average last frost, once the soil can be worked and is at least 40°F. In Boulder, that's roughly Apr 8–22 going by the typical date, or Apr 20 – May 4 going by the safer date. For a fall crop, sow by Jul 18, or by Jul 4 to be safe. That's 79 days back from the first-frost date.

When to plant lettuce (leaf) in Boulder

Hardy crop. CSU says lettuce (leaf) can go in as early as 2–4 weeks before the average last frost, once the soil can be worked and is at least 35°F. In Boulder, that's roughly Apr 8–22 going by the typical date, or Apr 20 – May 4 going by the safer date. For fall, count back 74 days from the first-frost date. That means sowing by Jul 23, or by Jul 9 to be safe.

When to plant carrots in Boulder

Semi-hardy crop. Per CSU, carrots can go in as early as 0–2 weeks before the average last frost: roughly Apr 22 – May 6 in Boulder (typical date) or May 4–18 (safer date). The soil should be at least 40°F. For fall, count back 84 days from the first-frost date. That means sowing by Jul 13, or by Jun 29 to be safe.

When to plant beans (snap) in Boulder

Tender crop. CSU says to sow beans (snap) around the average last frost, about May 6 in Boulder. If you want only a 1-in-10 chance of a later 32°F night, wait until May 18. Seeds need soil of at least 55°F. For a fall crop, sow by Jul 9, or by Jun 25 to be safe. That's 88 days back from the first-frost date.

When to plant summer squash in Boulder

Tender crop. CSU's timing for summer squash is around the average last frost, which is about May 6 in Boulder. For only a 1-in-10 chance of a later 32°F night, hold off until May 18. Seeds want soil at 60°F or warmer. For a fall crop, sow by Jul 19, or by Jul 5 to be safe. That's 78 days back from the first-frost date.

When to plant broccoli in Boulder

Hardy crop. CSU says broccoli can go in as early as 2–4 weeks before the average last frost, once the soil can be worked and is at least 40°F. In Boulder, that's roughly Apr 8–22 going by the typical date, or Apr 20 – May 4 going by the safer date. CSU's typical time from transplant to harvest for broccoli plants is 65 days. Set out on Apr 13, they would start producing around Jun 17, 110 days before the typical first frost (Oct 5). Fall broccoli: set transplants out by Jul 18. The date counts back from the typical first frost (Oct 5) by UNL Extension's method, using CSU's 65 days from transplant to harvest. Home-grown transplants need seeds started May 30 – Jun 13 (CSU: 5–7 weeks).

When to plant cabbage in Boulder

Hardy crop. CSU says cabbage can go in as early as 2–4 weeks before the average last frost, once the soil can be worked and is at least 40°F. In Boulder, that's roughly Apr 8–22 going by the typical date, or Apr 20 – May 4 going by the safer date. Using CSU's typical 85 days from transplant to harvest, cabbage plants set out on Apr 13 would start producing around Jul 7. That's 90 days before the typical first frost (Oct 5). Fall cabbage: set transplants out by Jun 28. The date counts back from the typical first frost (Oct 5) by UNL Extension's method, using CSU's 85 days from transplant to harvest. Home-grown transplants need seeds started May 10–24 (CSU: 5–7 weeks).

When to plant cauliflower in Boulder

Semi-hardy crop. Per CSU, cauliflower can go in as early as 0–2 weeks before the average last frost: roughly Apr 22 – May 6 in Boulder (typical date) or May 4–18 (safer date). The soil should be at least 40°F.

When to plant kohlrabi in Boulder

Hardy crop. CSU says kohlrabi can go in as early as 2–4 weeks before the average last frost, once the soil can be worked and is at least 40°F. In Boulder, that's roughly Apr 8–22 going by the typical date, or Apr 20 – May 4 going by the safer date. For fall, count back 64 days from the first-frost date. That means sowing by Aug 2, or by Jul 19 to be safe.

When to plant green onions in Boulder

Hardy crop. CSU says green onions can go in as early as 2–4 weeks before the average last frost, once the soil can be worked and is at least 35°F. In Boulder, that's roughly Apr 8–22 going by the typical date, or Apr 20 – May 4 going by the safer date. For a fall crop, sow by Jul 23, or by Jul 9 to be safe. That's 74 days back from the first-frost date.

When to plant radishes in Boulder

Hardy crop. CSU says radishes can go in as early as 2–4 weeks before the average last frost: roughly Apr 8–22 in Boulder using the typical date, or Apr 20 – May 4 using the safer one. Wait until the soil can be worked and is at least 40°F. For a fall crop, sow by Aug 22, or by Aug 8 to be safe. That's 44 days back from the first-frost date.

When to plant spinach in Boulder

Hardy crop. CSU says spinach can go in as early as 2–4 weeks before the average last frost: roughly Apr 8–22 in Boulder using the typical date, or Apr 20 – May 4 using the safer one. Wait until the soil can be worked and is at least 40°F. For a fall crop, sow by Aug 12, or by Jul 29 to be safe. That's 54 days back from the first-frost date.

When to plant turnips in Boulder

Hardy crop. CSU says turnips can go in as early as 2–4 weeks before the average last frost: roughly Apr 8–22 in Boulder using the typical date, or Apr 20 – May 4 using the safer one. Wait until the soil can be worked and is at least 40°F. For fall, sow by Aug 2 (Jul 19 to be safe), which is 64 days before the first-frost date.

When to plant beets in Boulder

Semi-hardy crop. CSU says beets can be planted as early as 0–2 weeks before the average last frost, in soil of at least 40°F. In Boulder, that's roughly Apr 22 – May 6 going by the typical date, or May 4–18 going by the safer date. For fall, sow by Jul 23 (Jul 9 to be safe), which is 74 days before the first-frost date.

When to plant swiss chard in Boulder

Semi-hardy crop. Per CSU, swiss chard can go in as early as 0–2 weeks before the average last frost: roughly Apr 22 – May 6 in Boulder (typical date) or May 4–18 (safer date). The soil should be at least 40°F. For fall, sow by Jul 23 (Jul 9 to be safe), which is 74 days before the first-frost date.

When to plant parsnips in Boulder

Semi-hardy crop. CSU says parsnips can be planted as early as 0–2 weeks before the average last frost, in soil of at least 35°F. In Boulder, that's roughly Apr 22 – May 6 going by the typical date, or May 4–18 going by the safer date.

When to plant sweet corn in Boulder

Tender crop. CSU says to sow sweet corn around the average last frost, about May 6 in Boulder. If you want only a 1-in-10 chance of a later 32°F night, wait until May 18. Seeds need soil of at least 50°F.

When to plant cucumbers in Boulder

Tender crop. Sow cucumbers around the average last frost, per CSU: about May 6 in Boulder. Waiting until May 18 cuts the chance of a later 32°F night to 1 in 10. Seeds need soil of at least 60°F. For fall, count back 83 days from the first-frost date. That means sowing by Jul 14, or by Jun 30 to be safe.

When to plant eggplant in Boulder

Very tender crop. Following CSU Extension's rule (2+ weeks after the average last frost), set eggplant out around May 20 with the typical date, May 25 for a balanced choice, or Jun 1 with the safer 10% date. Sow seeds indoors Mar 23 – Apr 13, 6–9 weeks before transplanting on May 25. Set out on May 25, eggplant plants would start producing around Jul 24, based on CSU's typical 60 days from transplant to harvest. That leaves 73 days before the typical first frost (Oct 5).

When to plant cantaloupe in Boulder

Very tender crop. CSU Extension says to plant cantaloupe 2+ weeks after the average last frost: about May 20 (typical date), May 25 (balanced) or Jun 1 (safer 10% date). Wait for soil of at least 60°F.

When to plant watermelon in Boulder

Very tender crop. Following CSU Extension's rule of 2+ weeks after the average last frost, plant watermelon around May 20 at the earliest, May 25 as a balanced choice, or Jun 1 to be safe. CSU's minimum soil temperature is 60°F.

When to plant winter squash in Boulder

Very tender crop. CSU Extension's rule is to plant winter squash at least 2 weeks after the average last frost. That's about May 20 using the typical date, May 25 as a balanced choice, or Jun 1 if you go by the safer 10% date. Seeds need soil of at least 60°F.

When to plant garlic in Boulder

CSU Extension's Colorado guidance is to plant garlic in early October, before October 15 (Oct 1–14). That's a fixed statewide window, not one computed from frost data. At Boulder, the typical first hard freeze (28°F) is Oct 15, 1 day after the window ends.

How these dates are calculated

CSU states its spring rules relative to “the average last spring frost.” We use the 50% date as that average and also show the 30% and 10% anchors. See the methodology for details and limitations.

FAQ

When should I start seeds indoors in Boulder?

Tomatoes: May 2–16. Peppers: Mar 30 – Apr 13. Both windows count back from a balanced (30%-risk) transplant date using CSU's transplant ages.

When should I plant tomatoes outside in Boulder?

Set tomatoes out about Jun 20. The date is the same at every risk level. CSU's rule of 2+ weeks after the average last frost would allow about May 20 here, but CSU also wants nights above 52°F, and the average nightly low at Boulder isn't above that until Jun 20.

What can I plant in Boulder in the fall?

These sowing deadlines count back from the typical first frost (Oct 5) using UNL Extension's method: peas by Jul 18; lettuce (leaf) by Jul 23; carrots by Jul 13; beans (snap) by Jul 9; summer squash by Jul 19; broccoli by Jul 18 (transplants); cabbage by Jun 28 (transplants); kohlrabi by Aug 2; green onions by Jul 23; radishes by Aug 22; spinach by Aug 12; turnips by Aug 2; beets by Jul 23; swiss chard by Jul 23; cucumbers by Jul 14. Plant garlic Oct 1–14.

When should I plant garlic in Boulder?

CSU Extension's Colorado guidance is early October, before October 15 (Oct 1–14).

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