Planting
Timing your Colorado garden planting right can mean the difference between a thriving harvest and a sad pile of frost-nipped seedlings. Colorado’s dramatic shifts—from late-spring freezes to early-summer heat—make getting the schedule wrong a costly mistake.
I’ve spent years growing 🌱 General Gardens across Colorado’s varied zones, and here’s what I’ve learned: the Front Range and Western Slope don’t play by the same rules. Whether you’re in Denver’s Zone 5 or Grand Junction’s Zone 7, knowing your last frost date is the key to success.
In this guide, I’ll break down exactly when to plant—from cool-season crops in April to heat-loving veggies in August***—plus how to adjust for high-altitude quirks. No more guessing whether your tomatoes will bolt before they ripen.
Ready to turn your Colorado garden into a productive powerhouse? Let’s dive into the month-by-month planting calendar that actually works for your region.
Colorado’s planting zones: how altitude & frost dates affect your schedule
Colorado’s diverse elevations create wildly different planting windows—what works in Denver (Zone 5) may fail in Grand Junction (Zone 7). The USDA Plant Hardiness Zone map is your first clue, but microclimates and frost dates are the real game-changers.
High-altitude gardens (like Aspen or Leadville) often have 30 fewer frost-free days than lowland areas, forcing later plantings. Let’s break down how to align your schedule with Colorado’s unique conditions.
Start by knowing your last average frost date—this is your planting deadline for warm-season crops. In Denver (Zone 5-6), the last frost typically hits April 15-30, while Colorado Springs (Zone 5-6) sees it May 1-15.
Meanwhile, Grand Junction (Zone 7-8) can plant 3-4 weeks earlier thanks to milder winters. For cool-season crops (like kale or peas), you can plant 6-8 weeks before your last frost date.
Elevation is everything in Colorado. Every 1,000 feet gain delays planting by about 1 week. That means a 6,000-foot garden (like Fort Collins) has a 6-week later start than a 4,000-foot garden (like Pueblo).
Use this rule: Subtract 1 week per 1,000 feet from your local frost date to estimate your planting window.
Here’s how elevation impacts your schedule:
- 4,000–5,000 ft (Pueblo, Colorado Springs): Last frost April 15–May 1
- 5,000–6,000 ft (Denver, Boulder): Last frost April 30–May 15
- 6,000–7,000 ft (Fort Collins, Estes Park): Last frost May 15–June 1
- 7,000+ ft (Leadville, Aspen): Last frost June 1–July 1
| Region | Avg. Last Frost | USDA Zone | Plant Warm Crops After | Frost-Free Days |
|---|---|---|---|---|
| Denver/Boulder | April 15–30 | 5–6 | May 15 | 90–120 |
| Colorado Springs | May 1–15 | 5–6 | May 30 | 100–130 |
| Grand Junction | March 15–April 1 | 7–8 | April 15 | 150–180 |
| Aspen/Leadville | June 1–July 1 | 4–5 | July 15 | 30–60 |
🌱 Key: Adjust dates 1 week later per 1,000 ft elevation gain.
For warm-season crops (tomatoes, peppers, corn), wait until soil temperatures hit 50°F (10°C)—a soil thermometer is worth its weight in gold.
In high-altitude areas, this could mean planting peppers in June instead of May. Cool-season crops (lettuce, spinach, broccoli) can handle light frosts and should go in 4–6 weeks before your last frost date.
Don’t forget first frost dates for fall planting! In Denver, expect frost by October 15, while Grand Junction may stretch to November 1. Fast-maturing varieties (like bush beans or radishes) are your best bet for late-summer plantings.
For perennials and shrubs, plant in early fall (September) to give roots time to establish before winter.
Pro tip: Check the National Weather Service or local Cooperative Extension office for your town’s 30-year frost averages. Microclimates—like urban heat islands or valley bottoms—can shift frost dates by 1–2 weeks. If you’re unsure, err on the side of planting later than earlier—your seedlings will thank you.
Finally, high-desert areas (like Fort Collins) have colder nights than Front Range valleys, while Western Slope gardens (like Pagosa Springs) face earlier frosts due to higher elevations. Always monitor local conditions and be ready to cover young plants with row fabric if frost threatens.
Understanding your local frost dates and elevation adjustments is the first step to a thriving Colorado garden. Once you’ve got those down, we’ll dive into month-by-month planting and season-extending tricks to make the most of your short growing season. 🌿
Month-by-month planting calendar for Colorado gardens: what to sow when
Colorado’s three distinct climate zones—Front Range, Western Slope, and high mountains—mean your planting schedule should align with your elevation and last frost dates.
For example, Denver’s average last frost is April 15, while Grand Junction’s is March 15, and high-altitude areas like Telluride may not thaw until May 15. Plan accordingly to avoid frost damage or wasted effort.
Start by calibrating your calendar to your USDA zone (5-8) and microclimate. Lowland areas like Pueblo can plant earlier than Denver, while mountain gardens must wait until soil warms to 50°F (10°C). Use this month-by-month guide to time your seed starts, transplants, and direct sowing for maximum success.
🌱 March: Indoor Starts & Cold-Hardy Crops Begin indoor seed starts for tomatoes, peppers, and eggplants under grow lights. In lowland zones, direct-sow peas, spinach, and lettuce once soil is workable. High-altitude gardeners should wait until late March or April to avoid frost.
🌿 April: Transplant & Direct-Sow Cool-Season Crops After your last frost date, transplant broccoli, cabbage, and kale. Direct-sow carrots, radishes, and beets in well-drained soil. For warm-season crops like beans and cucumbers, wait until soil reaches 60°F (15°C)—usually mid-to-late April in Denver.
In May, the real action begins. Once nighttime temperatures stay above 50°F (10°C), transplant tomatoes, peppers, and eggplants. Direct-sow cucumbers, corn, and melons in warm, sunny spots. High-altitude gardeners should wait until late May to avoid late frosts that can kill tender seedlings.
Don’t forget succession planting! In June and July, sow lettuce, beans, and radishes every 2-3 weeks to ensure a steady harvest. By August, shift focus to fall crops like kale, spinach, and carrots, which thrive in Colorado’s cooler autumn temperatures.
Extend your season into September and October by planting garlic, onions, and cold-hardy greens. Use row covers or cold frames to protect tender plants from early frosts. With these strategies, you’ll enjoy fresh produce well into November in lowland zones.