Plants
Timing your cabbage planting in Colorado isn’t just about following a calendar—it’s about outsmarting the state’s wild temperature swings and high-altitude quirks. One week too early, and your seedlings could turn into popsicles; one week late, and your plants bolt before you even taste that first harvest.
The key? Planting when soil temps hit 50°F and nights stay reliably above 40°F, which in Colorado means different weeks depending on whether you’re in Denver’s urban heat pockets or the Western Slope’s cooler valleys.
Let’s cut through the guesswork.
Whether you’re a first-time gardener or a seasoned grower, knowing the exact frost-free windows for your microclimate—like mid-April to early May for the Front Range or late May to June for higher elevations—can mean the difference between a thriving 🌱 crop and a sad, wilted disappointment.
I’ll break down how to adjust your schedule based on elevation, soil prep, and even Colorado’s notorious “June snow” surprises.
Here’s the game-changer: most Colorado gardeners miss the second planting window in late July for fall harvests, but with the right varieties and row covers, you can stretch your season well into October.
I’ll show you how to time it perfectly so you’re not scrambling when the first frost sneaks up—because in Colorado, that frost can arrive earlier than you think.
Ready to grow cabbage that’s head-turningly fresh? Grab your gloves, and let’s dive into the exact weeks to plant for your corner of Colorado—no more second-guessing, just confident, delicious harvests. Your taste buds (and your wallet) will thank you.
Colorado’s frost-free planting zones for cabbage: exact weeks by elevation
Colorado’s diverse elevations mean your cabbage planting window can vary by 4–6 weeks depending on where you live.
The Front Range (Denver, Boulder) typically has earlier last frosts (mid-April to early May) compared to mountain valleys (Fort Collins, Estes Park) or high-altitude areas (Leadville, Aspen), where frosts linger until June.
To avoid frost damage or heat bolting, align your planting with soil temperatures of 60–70°F—the sweet spot for germination.
Use Colorado State University’s frost-free date calculator (or local CoCoRaHS data) to pinpoint your microclimate’s last frost date. For example, Denver (5,280 ft) averages a May 15 last frost, while Grand Junction (4,450 ft) often sees frost-free conditions by April 15.
High-altitude areas like Telluride (8,750 ft) may not be frost-free until June 10. These differences directly impact your planting timeline.
Cabbage thrives in USDA Zones 4–7, but Colorado’s short growing season demands precision. Most varieties need 75–90 days to mature, so late spring plantings (after May 1) risk bolting before harvest. Conversely, fall plantings (August–September) can extend your season if you choose cold-hardy varieties like ‘January King’ or ‘Winterbor.’
| Elevation Range | Avg. Last Frost | Spring Planting Window | Fall Planting Window | Soil Temp. Goal |
|---|---|---|---|---|
| 4,000–6,000 ft (Denver, Colorado Springs, Fort Collins) | April 15–May 1 | April 20–May 15 | August 1–15 | 60–70°F |
| 6,000–8,000 ft (Estes Park, Durango, Salida) | May 1–15 | May 10–25 | July 20–August 5 | 60–70°F |
| 8,000+ ft (Leadville, Aspen, Telluride) | May 15–June 1 | May 25–June 10 | July 10–20 | 60–70°F |
| Western Slope (Grand Junction, Fruita) | April 1–15 | March 30–April 15 | July 15–August 1 | 55–65°F (earlier start) |
*Adjust dates 1–2 weeks earlier for urban heat islands (e.g., Denver) or later for cold pockets (e.g., mountain valleys).
For spring plantings, aim to transplant 4–6 weeks before your last frost. Start seeds indoors (under grow lights) by March 1–15 for lowland areas or April 1–15 for high-altitude zones. Harden off seedlings for 10–14 days before transplanting to outdoor beds once soil reaches 50°F.
Colorado’s fall cabbage is a game-changer for extending harvests. Plant 6–8 weeks before your first frost (typically August 1–15 for lowland areas, July 15–30 for high altitude). Use row covers to protect young plants from light frosts (28–32°F), which cabbage can tolerate.
Varieties like ‘Red Express’ or ‘Golden Acre’ are heat-tolerant and cold-hardy, making them ideal for Colorado’s unpredictable fall weather.
Pro tip: Monitor soil temperature with a soil thermometer—cabbage seeds won’t germinate below 50°F. If your soil is too cold, delay planting or use black plastic mulch to warm it 5–10°
How to stretch your cabbage season: succession planting for continuous harvests
Colorado’s short growing season means cabbage won’t give you one big harvest—unless you plan ahead. Succession planting lets you enjoy fresh heads from June through October by staggering plantings every 2–3 weeks.
This works best with cold-hardy varieties like ‘January King’ or ‘Golden Acre,’ which tolerate light frosts better than heat.
Start your first batch 4–6 weeks before your last frost date (typically mid-April in Denver). Then, plant 2–3 more batches in early June, mid-July, and late August to avoid bolting during Colorado’s 90°F+ heat waves. Each batch should mature before summer’s peak heat arrives.
Here’s my foolproof succession schedule for Colorado’s USDA Zones 4–7:
Pro tip: Direct-sow seedlings instead of transplanting to avoid shock. Colorado’s dry winds can stress young plants, so keep soil moist but not soggy during germination. A mulch layer (straw or grass clippings) helps retain moisture and regulates soil temperature.
Watch for bolting signs (long stems, yellow leaves) in summer plantings—this happens when days get too long or heat spikes. If you see it, harvest immediately or pull the plant to avoid spreading to others. Varieties like ‘Wax Leaf’ bolt more slowly in Colorado’s climate.
With this method, I’ve harvested 30+ heads per season in my Denver garden—enough for fresh slaw, fermented sauerkraut, and even gifts to neighbors! The key is adjusting for your microclimate (more on that in the next section). 🌱