When to Plant Cabbage in Colorado: Frost-Free Deadlines by Variety Type

Timing your cabbage planting in Colorado isn’t just about the calendar—it’s about beating frost, matching varieties to your microclimate, and avoiding the heartbreak of a crop that bolts before harvest.

With USDA zones 5-8 and unpredictable mountain weather, getting those seeds in the ground too early or too late can mean the difference between a bountiful fall harvest and a sad, shriveled mess.

Most gardeners in Denver and the Front Range know the drill: plant between March 15 and April 30 for spring crops and again from July 15 to August 15 for fall. But here’s the catch—your elevation changes everything.

High plains areas might need to wait until after April 15, while mountain regions could push planting back even further. The key is understanding your last frost date and choosing the right cabbage varieties that thrive in Colorado’s short growing seasons.

In this guide, I’ll break down the exact planting windows for head cabbage, bok choy, and kale, including how to adjust for Denver’s 5b-6b zones and the Western Slope’s drier climate.

You’ll also learn how to extend your harvest with successive plantings and avoid common mistakes that turn promising starts into disappointing failures. Let’s get those 🥬 plants growing strong!

Whether you’re a first-time gardener or a seasoned pro, nailing the timing will give you the confidence to grow cabbage that’s crisp, flavorful, and ready to harvest just in time for your favorite recipes. Ready to dig in?

Colorado cabbage planting deadlines by variety: early vs late season frost dates

Colorado’s microclimates mean your cabbage planting deadlines should vary based on elevation and location. The Front Range (Denver area) has different frost dates than the Western Slope or high plains.

For most Colorado regions, aim to plant head cabbage between March 15 and April 30 for spring harvests, and July 15 to August 15 for fall crops.

Your last frost date is critical—Denver typically sees its final frost around April 15, but higher elevations like Fort Collins or Boulder can experience frost until May 1. Meanwhile, the San Luis Valley may have frost as late as May 10.

Always check your local USDA Zone (Colorado ranges from Zone 5 to Zone 8) for precision.

Bok choy and kale are more cold-tolerant, allowing earlier plantings. You can start these as early as February 15 in Denver, while head cabbage needs warmer soil (45°F+) to thrive. For fall harvests, plant 8-10 weeks before your first frost—typically by July 15 in most regions.

For direct sowing, plant seeds 1/4 inch deep and 12-18 inches apart in rows spaced 24-30 inches apart. If transplanting seedlings, harden them off for 7-10 days before moving them outdoors. Transplanting is ideal for Colorado’s short growing season—start seeds indoors 6-8 weeks before your last frost.

In high-altitude areas like Aspen or Leadville, extend your growing season with row covers or cold frames. These can push your planting window back by 2-3 weeks in spring and fall.

For example, in Zone 5 areas, you might plant head cabbage as late as May 1 with protection.

Always monitor your local weather forecasts—unpredictable late frosts can still occur in May, especially in mountain valleys. If frost is forecasted, cover young plants with frost blankets or lightweight row covers.

For fall plantings, aim to harvest before first frost, which can arrive as early as September 30 in higher elevations.

Pro tip: Use black plastic mulch to warm soil faster in spring, helping seedlings establish quicker. This is especially useful in Denver’s clay soils, which can stay cold longer. Pair this with drip irrigation to maintain consistent moisture—drought stress is a common issue in Colorado’s dry climate.

For continuous harvests, stagger plantings every 2-3 weeks