Longmont, CO Vegetable Planting Calendar

What to plant now in Longmont

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 7, 50% risk), balanced = May 13 (30%), safe = May 22 (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 Longmont

What to plant in Longmont in February

• Start broccoli seeds indoors (Feb 25 – Mar 11)
• Start cabbage seeds indoors (Feb 25 – Mar 11)

What to plant in Longmont in March

• Start cauliflower seeds indoors (Mar 11–25)
• Start eggplant seeds indoors (Mar 25 – Apr 15)
• Start broccoli seeds indoors (Feb 25 – Mar 11)
• Start cabbage seeds indoors (Feb 25 – Mar 11)

What to plant in Longmont in April

• Start pepper seeds indoors (Apr 1–15)
• Onions (dry, from sets): plant sets outdoors (Apr 9 – May 8)
• Peas: direct sow outdoors (Apr 9 – May 8)
• Lettuce (leaf): direct sow outdoors (Apr 9 – May 8)
• Broccoli: transplant outdoors (Apr 9 – May 8)
• Cabbage: transplant outdoors (Apr 9 – May 8)
• Kohlrabi: direct sow outdoors (Apr 9 – May 8)
• Green onions: direct sow outdoors (Apr 9 – May 8)
• Radishes: direct sow outdoors (Apr 9 – May 8)
• Spinach: direct sow outdoors (Apr 9 – May 8)
• Turnips: direct sow outdoors (Apr 9 – May 8)
• Potatoes: plant (seed pieces) outdoors (Apr 23 – May 22)
• Carrots: direct sow outdoors (Apr 23 – May 22)
• Cauliflower: transplant outdoors (Apr 23 – May 22)
• Beets: direct sow outdoors (Apr 23 – May 22)
• Swiss chard: direct sow outdoors (Apr 23 – May 22)
• Parsnips: direct sow outdoors (Apr 23 – May 22)
• Start eggplant seeds indoors (Mar 25 – Apr 15)

What to plant in Longmont in May

• Start tomato seeds indoors (May 4–18)
• Beans (snap): direct sow outdoors (May 7–22)
• Summer squash: direct sow outdoors (May 7–22)
• Sweet corn: direct sow outdoors (May 7–22)
• Cucumbers: direct sow outdoors (May 7–22)
• Start cabbage seeds indoors for a fall crop (May 10–24)
• Peppers: transplant outdoors (May 21 – Jun 5)
• Eggplant: transplant outdoors (May 21 – Jun 5)
• Cantaloupe: direct sow outdoors (May 21 – Jun 5)
• Watermelon: direct sow outdoors (May 21 – Jun 5)
• Winter squash: direct sow outdoors (May 21 – Jun 5)
• Start broccoli seeds indoors for a fall crop (May 30 – Jun 13)
• Onions (dry, from sets): plant sets outdoors (Apr 9 – May 8)
• Peas: direct sow outdoors (Apr 9 – May 8)
• Lettuce (leaf): direct sow outdoors (Apr 9 – May 8)
• Broccoli: transplant outdoors (Apr 9 – May 8)
• Cabbage: transplant outdoors (Apr 9 – May 8)
• Kohlrabi: direct sow outdoors (Apr 9 – May 8)
• Green onions: direct sow outdoors (Apr 9 – May 8)
• Radishes: direct sow outdoors (Apr 9 – May 8)
• Spinach: direct sow outdoors (Apr 9 – May 8)
• Turnips: direct sow outdoors (Apr 9 – May 8)
• Potatoes: plant (seed pieces) outdoors (Apr 23 – May 22)
• Carrots: direct sow outdoors (Apr 23 – May 22)
• Cauliflower: transplant outdoors (Apr 23 – May 22)
• Beets: direct sow outdoors (Apr 23 – May 22)
• Swiss chard: direct sow outdoors (Apr 23 – May 22)
• Parsnips: direct sow outdoors (Apr 23 – May 22)

What to plant in Longmont in June

• Tomatoes: transplant outdoors (Jun 22)
• Last day to set out cabbage transplants for a fall harvest (by Jun 28)
• Peppers: transplant outdoors (May 21 – Jun 5)
• Eggplant: transplant outdoors (May 21 – Jun 5)
• Cantaloupe: direct sow outdoors (May 21 – Jun 5)
• Watermelon: direct sow outdoors (May 21 – Jun 5)
• Winter squash: direct sow outdoors (May 21 – Jun 5)
• Start broccoli seeds indoors for a fall crop (May 30 – Jun 13)

What to plant in Longmont 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 Longmont 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 Longmont in October

• Plant garlic cloves (Oct 1–14)

Crop-by-crop notes

When to plant tomatoes in Longmont

Very tender crop. CSU Extension's rules are to set tomatoes out at least 2 weeks after the average last frost and only once nights are above 52°F. In Longmont, the frost rule alone would allow about May 21, but the average nightly low at Longmont 2 ESE isn't above 52°F until Jun 22, so the night rule sets the date at every risk level: about Jun 22. Start seeds indoors May 4–18, 5–7 weeks before transplanting on Jun 22. CSU notes that nights under 55°F hurt fruit set. The normal low at Longmont 2 ESE climbs to 55°F on Jul 8. Set out on Jun 22, tomato plants would start producing around Aug 26, based on CSU's typical 65 days from transplant to harvest. That leaves 40 days before the typical first frost (Oct 5).

When to plant peppers in Longmont

Very tender crop. CSU Extension's rule is to set peppers out at least 2 weeks after the average last frost. That's about May 21 using the typical date, May 27 as a balanced choice, or Jun 5 if you go by the safer 10% date. Start seeds indoors Apr 1–15, 6–8 weeks before transplanting on May 27. Below 55°F at night, fruit set suffers (CSU). At Longmont 2 ESE, the normal low reaches 55°F on Jul 8. Using CSU's typical 70 days from transplant to harvest, pepper plants set out on May 27 would start producing around Aug 5. That's 61 days before the typical first frost (Oct 5).

When to plant potatoes in Longmont

Semi-hardy crop. Per CSU, potatoes can go in as early as 0–2 weeks before the average last frost: roughly Apr 23 – May 7 in Longmont (typical date) or May 8–22 (safer date). The soil should be at least 45°F.

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

Hardy crop. CSU says onions (dry, from sets) 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 Longmont, that's roughly Apr 9–23 going by the typical date, or Apr 24 – May 8 going by the safer date.

When to plant peas in Longmont

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 Longmont, that's roughly Apr 9–23 going by the typical date, or Apr 24 – May 8 going by the safer date. For fall, sow by Jul 18 (Jul 6 to be safe), which is 79 days before the first-frost date.

When to plant lettuce (leaf) in Longmont

Hardy crop. Per CSU, lettuce (leaf) can be planted as early as 2–4 weeks before the average last frost, as long as the soil is workable and at least 35°F. For Longmont, that works out to roughly Apr 9–23 (typical date) or Apr 24 – May 8 (safer date). For fall, sow by Jul 23 (Jul 11 to be safe), which is 74 days before the first-frost date.

When to plant carrots in Longmont

Semi-hardy crop. Per CSU, carrots can go in as early as 0–2 weeks before the average last frost: roughly Apr 23 – May 7 in Longmont (typical date) or May 8–22 (safer date). The soil should be at least 40°F. For fall, sow by Jul 13 (Jul 1 to be safe), which is 84 days before the first-frost date.

When to plant beans (snap) in Longmont

Tender crop. Sow beans (snap) around the average last frost, per CSU: about May 7 in Longmont. Waiting until May 22 cuts the chance of a later 32°F night to 1 in 10. Seeds need soil of at least 55°F. For fall, sow by Jul 9 (Jun 27 to be safe), which is 88 days before the first-frost date.

When to plant summer squash in Longmont

Tender crop. CSU says to sow summer squash around the average last frost, about May 7 in Longmont. If you want only a 1-in-10 chance of a later 32°F night, wait until May 22. Seeds need soil of at least 60°F. For a fall crop, sow by Jul 19, or by Jul 7 to be safe. That's 78 days back from the first-frost date.

When to plant broccoli in Longmont

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 Longmont, that's roughly Apr 9–23 going by the typical date, or Apr 24 – May 8 going by the safer date. Set out on Apr 15, broccoli plants would start producing around Jun 19, based on CSU's typical 65 days from transplant to harvest. That leaves 108 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 Longmont

Hardy crop. Per CSU, cabbage can be planted as early as 2–4 weeks before the average last frost, as long as the soil is workable and at least 40°F. For Longmont, that works out to roughly Apr 9–23 (typical date) or Apr 24 – May 8 (safer date). CSU's typical time from transplant to harvest for cabbage plants is 85 days. Set out on Apr 15, they would start producing around Jul 9, 88 days before the typical first frost (Oct 5). For a fall harvest of cabbage, get transplants in the ground by Jun 28 (UNL Extension count-back from the typical first frost, Oct 5, with CSU's 85 days from transplant to harvest). To raise your own, sow seeds May 10–24, 5–7 weeks ahead (CSU).

When to plant cauliflower in Longmont

Semi-hardy crop. CSU says cauliflower can be planted as early as 0–2 weeks before the average last frost, in soil of at least 40°F. In Longmont, that's roughly Apr 23 – May 7 going by the typical date, or May 8–22 going by the safer date.

When to plant kohlrabi in Longmont

Hardy crop. Per CSU, kohlrabi can be planted as early as 2–4 weeks before the average last frost, as long as the soil is workable and at least 40°F. For Longmont, that works out to roughly Apr 9–23 (typical date) or Apr 24 – May 8 (safer date). For fall, count back 64 days from the first-frost date. That means sowing by Aug 2, or by Jul 21 to be safe.

When to plant green onions in Longmont

Hardy crop. Per CSU, green onions can be planted as early as 2–4 weeks before the average last frost, as long as the soil is workable and at least 35°F. For Longmont, that works out to roughly Apr 9–23 (typical date) or Apr 24 – May 8 (safer date). For fall, sow by Jul 23 (Jul 11 to be safe), which is 74 days before the first-frost date.

When to plant radishes in Longmont

Hardy crop. CSU says radishes can go in as early as 2–4 weeks before the average last frost: roughly Apr 9–23 in Longmont using the typical date, or Apr 24 – May 8 using the safer one. Wait until the soil can be worked and is at least 40°F. For fall, sow by Aug 22 (Aug 10 to be safe), which is 44 days before the first-frost date.

When to plant spinach in Longmont

Hardy crop. CSU says spinach 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 Longmont, that's roughly Apr 9–23 going by the typical date, or Apr 24 – May 8 going by the safer date. For fall, sow by Aug 12 (Jul 31 to be safe), which is 54 days before the first-frost date.

When to plant turnips in Longmont

Hardy crop. CSU says turnips 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 Longmont, that's roughly Apr 9–23 going by the typical date, or Apr 24 – May 8 going by the safer date. For a fall crop, sow by Aug 2, or by Jul 21 to be safe. That's 64 days back from the first-frost date.

When to plant beets in Longmont

Semi-hardy crop. CSU allows planting beets as early as 0–2 weeks before the average last frost, in soil at 40°F or warmer. For Longmont, that's roughly Apr 23 – May 7 by the typical date or May 8–22 by the safer date. For fall, count back 74 days from the first-frost date. That means sowing by Jul 23, or by Jul 11 to be safe.

When to plant swiss chard in Longmont

Semi-hardy crop. Per CSU, swiss chard can go in as early as 0–2 weeks before the average last frost: roughly Apr 23 – May 7 in Longmont (typical date) or May 8–22 (safer date). The soil should be at least 40°F. For fall, sow by Jul 23 (Jul 11 to be safe), which is 74 days before the first-frost date.

When to plant parsnips in Longmont

Semi-hardy crop. Per CSU, parsnips can go in as early as 0–2 weeks before the average last frost: roughly Apr 23 – May 7 in Longmont (typical date) or May 8–22 (safer date). The soil should be at least 35°F.

When to plant sweet corn in Longmont

Tender crop. CSU's timing for sweet corn is around the average last frost, which is about May 7 in Longmont. For only a 1-in-10 chance of a later 32°F night, hold off until May 22. Seeds want soil at 50°F or warmer.

When to plant cucumbers in Longmont

Tender crop. CSU's timing for cucumbers is around the average last frost, which is about May 7 in Longmont. For only a 1-in-10 chance of a later 32°F night, hold off until May 22. Seeds want soil at 60°F or warmer. For a fall crop, sow by Jul 14, or by Jul 2 to be safe. That's 83 days back from the first-frost date.

When to plant eggplant in Longmont

Very tender crop. CSU Extension's rule is 2+ weeks after the average last frost, which puts eggplant outside around May 21 (typical date), May 27 (balanced) or Jun 5 (safer 10% date). Start seeds indoors Mar 25 – Apr 15, 6–9 weeks ahead of transplanting on May 27. Set out on May 27, eggplant plants would start producing around Jul 26, based on CSU's typical 60 days from transplant to harvest. That leaves 71 days before the typical first frost (Oct 5).

When to plant cantaloupe in Longmont

Very tender crop. Following CSU Extension's rule of 2+ weeks after the average last frost, plant cantaloupe around May 21 at the earliest, May 27 as a balanced choice, or Jun 5 to be safe. CSU's minimum soil temperature is 60°F.

When to plant watermelon in Longmont

Very tender crop. Following CSU Extension's rule of 2+ weeks after the average last frost, plant watermelon around May 21 at the earliest, May 27 as a balanced choice, or Jun 5 to be safe. CSU's minimum soil temperature is 60°F.

When to plant winter squash in Longmont

Very tender crop. CSU Extension says to plant winter squash 2+ weeks after the average last frost: about May 21 (typical date), May 27 (balanced) or Jun 5 (safer 10% date). Wait for soil of at least 60°F.

When to plant garlic in Longmont

Plant garlic in early October, before October 15 (Oct 1–14), per CSU Extension's Colorado guidance. The window is fixed statewide and isn't based on frost data. At Longmont 2 ESE, the typical first hard freeze (28°F) comes on Oct 12, no later than the window's last day.

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 Longmont?

Start tomatoes May 4–18 and peppers Apr 1–15. Both dates count back from a balanced (30%-risk) transplant date using CSU's transplant ages.

When should I plant tomatoes outside in Longmont?

Set tomatoes out about Jun 22. The date is the same at every risk level. CSU's rule of 2+ weeks after the average last frost would allow about May 21 here, but CSU also wants nights above 52°F, and the average nightly low at Longmont 2 ESE isn't above that until Jun 22.

What can I plant in Longmont in the fall?

Counting back from the typical first frost (Oct 5) with 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. Garlic goes in Oct 1–14.

When should I plant garlic in Longmont?

Early October, before October 15 (Oct 1–14). That's CSU Extension's guidance for Colorado.

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