When to Plant Broccoli in Colorado (2026 Guide)

If you're considering planting broccoli in Colorado, understanding your local climate and frost dates is crucial for a successful harvest. In many regions, the last spring frost occurs around May 5, while fall frost can arrive as early as September 27. This means that timing your planting can be the difference between a thriving crop and a disappointing yield.

Broccoli is a cool-season crop, which means it thrives when temperatures are mild, ideally between 45°F and 75°F. The goal is to ensure that the heads develop during this cool weather before the summer heat arrives. This guide will help you navigate the planting windows and tips specific to Colorado's unique growing conditions.

Depending on your location, the optimal planting dates for broccoli can vary significantly. Those in zones with earlier last frosts should aim to plant as soon as conditions allow. Take the time to learn about your USDA hardiness zone and follow the recommendations below to maximize your broccoli harvest in the varying climates of Colorado.

Planting Schedule by USDA Zone in Colorado

Zone	Indoor start	Transplant out	Direct sow	Harvest
Zone 5b	Start March 1 – March 15, ~6–8 weeks before May 5	Transplant outdoors after May 5, ~1-2 weeks post-last frost	Direct sow after May 5	Harvest from mid-June to late August
Zone 5a	Start March 10 – March 24, ~6–8 weeks before May 17	Transplant outdoors after May 17, ~1-2 weeks post-last frost	Direct sow after May 17	Harvest from late June to mid-August
Zone 6a	Start March 1 – March 15, ~6–8 weeks before April 25	Transplant outdoors after April 25, ~1-2 weeks post-last frost	Direct sow after April 25	Harvest from mid-June to late September

Broccoli Planting Windows in Colorado

Indoor start: For most areas in Colorado, you should start broccoli indoors from March 1 to March 24.
Transplant outdoors: Transplant broccoli outdoors after the last frost, which varies from May 5 to May 17 depending on your zone.
Harvest: Broccoli can typically be harvested from mid-June to late September, depending on the planting timing and regional climate.

Common Mistakes Growing Broccoli in Colorado

One common mistake in Colorado is planting broccoli too late in the season. Many gardeners underestimate the impact of the late May frosts. Even in warmer zones, planting after the last frost can lead to poor growth due to high summer temperatures.
Using inadequate cover for young broccoli plants can result in pest infestations, especially from cabbage worms. In Colorado, these pests can become rampant, so securing your plants immediately after transplanting is essential to avoid crop loss.
Ignoring soil quality is another error that many novice gardeners in Colorado make. Alkaline soils are prevalent in many areas, and without proper soil tests and amendments, broccoli may not thrive, leading to stunted growth and reduced yields.
Many gardeners also fail to realize that broccoli needs consistent watering, especially during dry spells. Colorado's semi-arid climate can cause the soil to dry out quickly, making regular irrigation crucial for healthy broccoli development.
Finally, some gardeners overlook the benefits of succession planting. Given Colorado's varied climate, planting multiple crops at staggered intervals can ensure an extended harvest throughout the growing season instead of relying on one crop.

Frequently Asked Questions

What if I'm in a cold pocket of Colorado?

If you're located in a colder area, wait until at least the recommended last frost date to plant broccoli. Additionally, consider using row covers for extra warmth and protection from sudden temperature drops.

Can I still plant broccoli in May?

Yes, you can plant broccoli in May, especially if you are using fast-growing varieties. Just ensure you're planting before the last frost date for your zone to avoid frost damage.

How can I tell when to harvest my broccoli?

Harvest broccoli when the heads are dark green and dense, with tightly closed buds. Avoid letting yellow flowers appear, as this indicates the head is past its prime.

What's the best way to manage pests on my broccoli?

Using row covers after transplanting can help exclude pests. If pests still appear, a spray of Bt (Bacillus thuringiensis) is an effective solution and safe for beneficial insects.

Are there specific broccoli varieties suited for Colorado's climate?

Yes, varieties like 'Premium Crop' and 'Packman' are well-suited for spring planting in Colorado, while 'Belstar' and 'Green Magic' excel in the fall.

Keep Learning

Typical fall sowing window for Broccoli in Colorado: August 2 – August 2.