Castle Rock, CO Vegetable Planting Calendar

What to plant now in Castle Rock

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 9, 50% risk), balanced = May 15 (30%), safe = May 24 (10%). For hardy crops the cell shows the CSU “as early as” window.

A soil thermometer helps here. CSU recommends checking soil temperature at 4 inches (6 inches for beans) before sowing. NOAA doesn't publish soil-temperature normals, so instead of a date, each crop shows CSU's minimum soil temperature.

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 Castle Rock

What to plant in Castle Rock in February

• Start broccoli seeds indoors (Feb 27 – Mar 13)
• Start cabbage seeds indoors (Feb 27 – Mar 13)

What to plant in Castle Rock in March

• Start cauliflower seeds indoors (Mar 13–27)
• Start eggplant seeds indoors (Mar 27 – Apr 17)
• Start broccoli seeds indoors (Feb 27 – Mar 13)
• Start cabbage seeds indoors (Feb 27 – Mar 13)

What to plant in Castle Rock in April

• Start pepper seeds indoors (Apr 3–17)
• Onions (dry, from sets): plant sets outdoors (Apr 11 – May 10)
• Peas: direct sow outdoors (Apr 11 – May 10)
• Lettuce (leaf): direct sow outdoors (Apr 11 – May 10)
• Broccoli: transplant outdoors (Apr 11 – May 10)
• Cabbage: transplant outdoors (Apr 11 – May 10)
• Kohlrabi: direct sow outdoors (Apr 11 – May 10)
• Green onions: direct sow outdoors (Apr 11 – May 10)
• Radishes: direct sow outdoors (Apr 11 – May 10)
• Spinach: direct sow outdoors (Apr 11 – May 10)
• Turnips: direct sow outdoors (Apr 11 – May 10)
• Potatoes: plant (seed pieces) outdoors (Apr 25 – May 24)
• Carrots: direct sow outdoors (Apr 25 – May 24)
• Cauliflower: transplant outdoors (Apr 25 – May 24)
• Beets: direct sow outdoors (Apr 25 – May 24)
• Swiss chard: direct sow outdoors (Apr 25 – May 24)
• Parsnips: direct sow outdoors (Apr 25 – May 24)
• Start eggplant seeds indoors (Mar 27 – Apr 17)

What to plant in Castle Rock in May

• Start tomato seeds indoors (May 4–18)
• Start cabbage seeds indoors for a fall crop (May 7–21)
• Beans (snap): direct sow outdoors (May 9–24)
• Summer squash: direct sow outdoors (May 9–24)
• Sweet corn: direct sow outdoors (May 9–24)
• Cucumbers: direct sow outdoors (May 9–24)
• Peppers: transplant outdoors (May 23 – Jun 7)
• Eggplant: transplant outdoors (May 23 – Jun 7)
• Cantaloupe: direct sow outdoors (May 23 – Jun 7)
• Watermelon: direct sow outdoors (May 23 – Jun 7)
• Winter squash: direct sow outdoors (May 23 – Jun 7)
• Start broccoli seeds indoors for a fall crop (May 27 – Jun 10)
• Onions (dry, from sets): plant sets outdoors (Apr 11 – May 10)
• Peas: direct sow outdoors (Apr 11 – May 10)
• Lettuce (leaf): direct sow outdoors (Apr 11 – May 10)
• Broccoli: transplant outdoors (Apr 11 – May 10)
• Cabbage: transplant outdoors (Apr 11 – May 10)
• Kohlrabi: direct sow outdoors (Apr 11 – May 10)
• Green onions: direct sow outdoors (Apr 11 – May 10)
• Radishes: direct sow outdoors (Apr 11 – May 10)
• Spinach: direct sow outdoors (Apr 11 – May 10)
• Turnips: direct sow outdoors (Apr 11 – May 10)
• Potatoes: plant (seed pieces) outdoors (Apr 25 – May 24)
• Carrots: direct sow outdoors (Apr 25 – May 24)
• Cauliflower: transplant outdoors (Apr 25 – May 24)
• Beets: direct sow outdoors (Apr 25 – May 24)
• Swiss chard: direct sow outdoors (Apr 25 – May 24)
• Parsnips: direct sow outdoors (Apr 25 – May 24)

What to plant in Castle Rock in June

• Tomatoes: transplant outdoors (Jun 22)
• Last day to set out cabbage transplants for a fall harvest (by Jun 25)
• Peppers: transplant outdoors (May 23 – Jun 7)
• Eggplant: transplant outdoors (May 23 – Jun 7)
• Cantaloupe: direct sow outdoors (May 23 – Jun 7)
• Watermelon: direct sow outdoors (May 23 – Jun 7)
• Winter squash: direct sow outdoors (May 23 – Jun 7)
• Start broccoli seeds indoors for a fall crop (May 27 – Jun 10)

What to plant in Castle Rock in July

• Last day to sow beans (snap) for a fall harvest (by Jul 6)
• Last day to sow carrots for a fall harvest (by Jul 10)
• Last day to sow cucumbers for a fall harvest (by Jul 11)
• Last day to sow peas for a fall harvest (by Jul 15)
• Last day to set out broccoli transplants for a fall harvest (by Jul 15)
• Last day to sow summer squash for a fall harvest (by Jul 16)
• Last day to sow lettuce (leaf) for a fall harvest (by Jul 20)
• Last day to sow green onions for a fall harvest (by Jul 20)
• Last day to sow beets for a fall harvest (by Jul 20)
• Last day to sow swiss chard for a fall harvest (by Jul 20)
• Last day to sow kohlrabi for a fall harvest (by Jul 30)
• Last day to sow turnips for a fall harvest (by Jul 30)

What to plant in Castle Rock in August

• Last day to sow spinach for a fall harvest (by Aug 9)
• Last day to sow radishes for a fall harvest (by Aug 19)

What to plant in Castle Rock in October

• Plant garlic cloves (Oct 1–14)

Crop-by-crop notes

When to plant tomatoes in Castle Rock

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 Castle Rock, the frost rule alone would allow about May 23, but the average nightly low at Castle Rock 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 Castle Rock climbs to 55°F on Jul 4. Using CSU's typical 65 days from transplant to harvest, tomato plants set out on Jun 22 would start producing around Aug 26. That's 37 days before the typical first frost (Oct 2).

When to plant peppers in Castle Rock

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 23 using the typical date, May 29 as a balanced choice, or Jun 7 if you go by the safer 10% date. Start seeds indoors Apr 3–17, 6–8 weeks before transplanting on May 29. Below 55°F at night, fruit set suffers (CSU). At Castle Rock, the normal low reaches 55°F on Jul 4. Using CSU's typical 70 days from transplant to harvest, pepper plants set out on May 29 would start producing around Aug 7. That's 56 days before the typical first frost (Oct 2).

When to plant potatoes in Castle Rock

Semi-hardy crop. CSU says potatoes can be planted as early as 0–2 weeks before the average last frost, in soil of at least 45°F. In Castle Rock, that's roughly Apr 25 – May 9 going by the typical date, or May 10–24 going by the safer date.

When to plant onions (dry, from sets) in Castle Rock

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 Castle Rock, that's roughly Apr 11–25 going by the typical date, or Apr 26 – May 10 going by the safer date.

When to plant peas in Castle Rock

Hardy crop. CSU says peas can go in as early as 2–4 weeks before the average last frost: roughly Apr 11–25 in Castle Rock using the typical date, or Apr 26 – May 10 using the safer one. Wait until the soil can be worked and is at least 40°F. For fall, sow by Jul 15 (Jun 30 to be safe), which is 79 days before the first-frost date.

When to plant lettuce (leaf) in Castle Rock

Hardy crop. CSU says lettuce (leaf) can go in as early as 2–4 weeks before the average last frost: roughly Apr 11–25 in Castle Rock using the typical date, or Apr 26 – May 10 using the safer one. Wait until the soil can be worked and is at least 35°F. For fall, count back 74 days from the first-frost date. That means sowing by Jul 20, or by Jul 5 to be safe.

When to plant carrots in Castle Rock

Semi-hardy crop. Per CSU, carrots can go in as early as 0–2 weeks before the average last frost: roughly Apr 25 – May 9 in Castle Rock (typical date) or May 10–24 (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 10, or by Jun 25 to be safe.

When to plant beans (snap) in Castle Rock

Tender crop. CSU says to sow beans (snap) around the average last frost, about May 9 in Castle Rock. If you want only a 1-in-10 chance of a later 32°F night, wait until May 24. Seeds need soil of at least 55°F. For a fall crop, sow by Jul 6, or by Jun 21 to be safe. That's 88 days back from the first-frost date.

When to plant summer squash in Castle Rock

Tender crop. Sow summer squash around the average last frost, per CSU: about May 9 in Castle Rock. Waiting until May 24 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 78 days from the first-frost date. That means sowing by Jul 16, or by Jul 1 to be safe.

When to plant broccoli in Castle Rock

Hardy crop. Per CSU, broccoli 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 Castle Rock, that works out to roughly Apr 11–25 (typical date) or Apr 26 – May 10 (safer date). Using CSU's typical 65 days from transplant to harvest, broccoli plants set out on Apr 17 would start producing around Jun 21. That's 103 days before the typical first frost (Oct 2). For a fall harvest of broccoli, get transplants in the ground by Jul 15 (UNL Extension count-back from the typical first frost, Oct 2, with CSU's 65 days from transplant to harvest). To raise your own, sow seeds May 27 – Jun 10, 5–7 weeks ahead (CSU).

When to plant cabbage in Castle Rock

Hardy crop. CSU says cabbage can go in as early as 2–4 weeks before the average last frost: roughly Apr 11–25 in Castle Rock using the typical date, or Apr 26 – May 10 using the safer one. Wait until the soil can be worked and is at least 40°F. Set out on Apr 17, cabbage plants would start producing around Jul 11, based on CSU's typical 85 days from transplant to harvest. That leaves 83 days before the typical first frost (Oct 2). For a fall crop, set cabbage transplants out by Jun 25. That's UNL Extension's count-back from the typical first frost (Oct 2), using CSU's 85 days from transplant to harvest. If you grow your own transplants, start seeds May 7–21 (CSU: 5–7 weeks to transplant size).

When to plant cauliflower in Castle Rock

Semi-hardy crop. Per CSU, cauliflower can go in as early as 0–2 weeks before the average last frost: roughly Apr 25 – May 9 in Castle Rock (typical date) or May 10–24 (safer date). The soil should be at least 40°F.

When to plant kohlrabi in Castle Rock

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 Castle Rock, that's roughly Apr 11–25 going by the typical date, or Apr 26 – May 10 going by the safer date. For fall, count back 64 days from the first-frost date. That means sowing by Jul 30, or by Jul 15 to be safe.

When to plant green onions in Castle Rock

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 Castle Rock, that works out to roughly Apr 11–25 (typical date) or Apr 26 – May 10 (safer date). For fall, sow by Jul 20 (Jul 5 to be safe), which is 74 days before the first-frost date.

When to plant radishes in Castle Rock

Hardy crop. CSU says radishes can go in as early as 2–4 weeks before the average last frost: roughly Apr 11–25 in Castle Rock using the typical date, or Apr 26 – May 10 using the safer one. Wait until the soil can be worked and is at least 40°F. For fall, count back 44 days from the first-frost date. That means sowing by Aug 19, or by Aug 4 to be safe.

When to plant spinach in Castle Rock

Hardy crop. CSU says spinach can go in as early as 2–4 weeks before the average last frost: roughly Apr 11–25 in Castle Rock using the typical date, or Apr 26 – May 10 using the safer one. Wait until the soil can be worked and is at least 40°F. For fall, count back 54 days from the first-frost date. That means sowing by Aug 9, or by Jul 25 to be safe.

When to plant turnips in Castle Rock

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 Castle Rock, that's roughly Apr 11–25 going by the typical date, or Apr 26 – May 10 going by the safer date. For fall, count back 64 days from the first-frost date. That means sowing by Jul 30, or by Jul 15 to be safe.

When to plant beets in Castle Rock

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 Castle Rock, that's roughly Apr 25 – May 9 going by the typical date, or May 10–24 going by the safer date. For fall, count back 74 days from the first-frost date. That means sowing by Jul 20, or by Jul 5 to be safe.

When to plant swiss chard in Castle Rock

Semi-hardy crop. CSU allows planting swiss chard as early as 0–2 weeks before the average last frost, in soil at 40°F or warmer. For Castle Rock, that's roughly Apr 25 – May 9 by the typical date or May 10–24 by the safer date. For fall, count back 74 days from the first-frost date. That means sowing by Jul 20, or by Jul 5 to be safe.

When to plant parsnips in Castle Rock

Semi-hardy crop. Per CSU, parsnips can go in as early as 0–2 weeks before the average last frost: roughly Apr 25 – May 9 in Castle Rock (typical date) or May 10–24 (safer date). The soil should be at least 35°F.

When to plant sweet corn in Castle Rock

Tender crop. CSU says to sow sweet corn around the average last frost, about May 9 in Castle Rock. If you want only a 1-in-10 chance of a later 32°F night, wait until May 24. Seeds need soil of at least 50°F.

When to plant cucumbers in Castle Rock

Tender crop. CSU's timing for cucumbers is around the average last frost, which is about May 9 in Castle Rock. For only a 1-in-10 chance of a later 32°F night, hold off until May 24. Seeds want soil at 60°F or warmer. For fall, sow by Jul 11 (Jun 26 to be safe), which is 83 days before the first-frost date.

When to plant eggplant in Castle Rock

Very tender crop. CSU Extension's rule is 2+ weeks after the average last frost, which puts eggplant outside around May 23 (typical date), May 29 (balanced) or Jun 7 (safer 10% date). Start seeds indoors Mar 27 – Apr 17, 6–9 weeks ahead of transplanting on May 29. CSU's typical time from transplant to harvest for eggplant plants is 60 days. Set out on May 29, they would start producing around Jul 28, 66 days before the typical first frost (Oct 2).

When to plant cantaloupe in Castle Rock

Very tender crop. Following CSU Extension's rule of 2+ weeks after the average last frost, plant cantaloupe around May 23 at the earliest, May 29 as a balanced choice, or Jun 7 to be safe. CSU's minimum soil temperature is 60°F.

When to plant watermelon in Castle Rock

Very tender crop. CSU Extension's rule is to plant watermelon at least 2 weeks after the average last frost. That's about May 23 using the typical date, May 29 as a balanced choice, or Jun 7 if you go by the safer 10% date. Seeds need soil of at least 60°F.

When to plant winter squash in Castle Rock

Very tender crop. CSU Extension says to plant winter squash 2+ weeks after the average last frost: about May 23 (typical date), May 29 (balanced) or Jun 7 (safer 10% date). Wait for soil of at least 60°F.

When to plant garlic in Castle Rock

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 Castle Rock, 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 Castle Rock?

Sow tomatoes indoors May 4–18 and peppers Apr 3–17. We work back from a balanced (30%-risk) transplant date using CSU's transplant ages.

When should I plant tomatoes outside in Castle Rock?

About Jun 22, at every risk level. CSU wants tomatoes out 2+ weeks after the average last frost (that rule alone gives about May 23 here) and nights above 52°F. At Castle Rock, the average nightly low first rises above 52°F on Jun 22, later than the frost-rule date, so the night rule sets the date.

What can I plant in Castle Rock in the fall?

Based on UNL Extension's count-back from the typical first frost (Oct 2), sow peas by Jul 15; lettuce (leaf) by Jul 20; carrots by Jul 10; beans (snap) by Jul 6; summer squash by Jul 16; broccoli by Jul 15 (transplants); cabbage by Jun 25 (transplants); kohlrabi by Jul 30; green onions by Jul 20; radishes by Aug 19; spinach by Aug 9; turnips by Jul 30; beets by Jul 20; swiss chard by Jul 20; cucumbers by Jul 11. Garlic goes in Oct 1–14.

When should I plant garlic in Castle Rock?

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

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