Knowing exactly when to plant in Colorado is the single most important factor for your garden’s success. Our state’s unique climate, with its late spring frosts, intense sun, and rapid weather shifts, demands careful timing. Get it right, and you’ll be rewarded with a thriving, productive garden. Get it wrong, and you might face disappointing setbacks.
This guide cuts through the complexity. We’ll provide clear, zone-specific planting calendars and practical tips to help you work with Colorado’s seasons, not against them. Let’s get your garden started on the perfect schedule.
When To Plant In Colorado
This core principle is your foundation. Colorado’s average last spring frost date is your starting gun for most summer crops. However, this date varies dramatically by elevation and location. A garden in Grand Junction (4,500 ft) faces different risks than one in Leadville (10,000 ft).
Always check your specific local frost dates. Your county extension office is a fantastic resource for hyper-local data. As a general rule, the front range urban corridor from Fort Collins to Colorado Springs sees its last frost around May 5th. Mountain towns may wait until mid-June or even early July.
Understanding Colorado’s Planting Zones
The USDA Plant Hardiness Zone Map is essential, but it’s just one tool. It tells you the average annual extreme minimum winter temperature, helping you choose perennial plants that will survive our cold winters. Most of Colorado’s populated front range falls into zones 5b (-15°F to -10°F) and 6a (-10°F to -5°F).
More crucial for planting times is your growing season length—the number of days between your last spring frost and first fall frost. This can range from over 150 days in Pueblo to under 90 days in high mountain valleys. Always select vegetable varieties with a “days to maturity” shorter than your growing season.
Your Spring Planting Schedule (Vegetables & Annuals)
Spring planting happens in waves, not all at once. We categorize plants by their cold tolerance.
Very Hardy Crops (Plant 4-6 Weeks Before Last Frost)
These seeds can be sown directly in the garden as soon as the soil is workable (not frozen or soggy). They tolerate frost and even a light snow.
- Peas
- Spinach
- Kale
- Radishes
- Carrots
- Beets
- Potatoes (plant seed potatoes)
Hardy Crops (Plant 2-4 Weeks Before Last Frost)
These can handle a light frost. You can direct seed or transplant seedlings you started indoors or bought.
- Lettuce
- Swiss Chard
- Broccoli
- Cabbage
- Onion sets
Tender Crops (Plant After Last Frost)
These are killed by frost. Wait until all danger has passed and soil has warmed. Rushing these is a common mistake.
- Beans (sow directly)
- Corn (sow directly)
- Cucumbers (transplant or direct sow)
- Summer Squash (transplant or direct sow)
Very Tender Crops (Plant 1-2 Weeks After Last Frost)
These need warm soil and warm nights. Planting in cold soil will stunt them.
- Tomatoes (transplant)
- Peppers (transplant)
- Eggplant (transplant)
- Basil (transplant)
- Winter Squash & Pumpkins (transplant or direct sow)
Your Fall Planting Schedule (The Secret to Extended Harvest)
Many Colorado gardeners miss the opportunity for a fall garden, which is often more productive and pest-free than spring. You work backwards from your average first fall frost date.
For hardy crops like kale and carrots, count back from your first frost date using the “days to maturity” on the seed packet. For many greens, you can plant in mid-to-late summer for a sweet, crisp fall harvest. Some, like spinach and mache, can even survive winter under a thick mulch or cold frame for an early spring harvest.
Tips for Navigating Colorado’s Weather Challenges
Our weather is unpredictable. Here’s how to adapt.
- Use Season Extenders: Invest in simple tools like floating row covers, cold frames, or wall-o-waters. These protect tender plants from surprise late frosts and can add weeks to your season on both ends.
- Harden Off Transplants: Never move indoor-started seedlings directly into the garden. Acclimate them to sun and wind over 7-10 days by placing them outdoors for increasing periods each day.
- Watch the Soil, Not Just the Calendar: If spring is cold and wet, delay planting warm-season crops even if the calendar says it’s time. Cold, wet soil rots seeds and stunts roots.
- Water Wisely at Planting: Water new seeds and transplants gently but deeply. Our low humidity and wind can dry soil surface quickly, so check moisture daily.
Step-by-Step: Preparing Your Garden Bed for Planting
- Test Your Soil: Colorado soils are often clay-heavy and alkaline. A simple test from your extension office tells you what to amend.
- Amend with Compost: Add 2-4 inches of well-finished compost and work it into the top 6-8 inches of soil. This improves drainage in clay and water retention in sand.
- Consider Raised Beds: They warm up faster in spring, drain better, and allow you to control soil quality—a huge advantage.
- Wait for the Right Conditions: Grab a handful of soil. If you can squeeze it into a muddy ball, it’s too wet. If it crumbles freely, it’s ready.
FAQ: Your Colorado Planting Questions Answered
When is it safe to plant tomatoes in Colorado?
Wait until at least 1-2 weeks after your last average spring frost date. For Denver, that’s typically around May 15th. Use protective covers if an late frost threatens after planting.
What can I plant early in Colorado spring?
Focus on hardy crops like peas, spinach, radishes, kale, and potatoes. These thrive in cool weather and can be planted as soon as soil is workable.
How do I find my exact frost dates?
Search for “frost dates” along with your town name, or visit the National Gardening Association’s website and enter your zip code. Your local master gardener program also has this info.
Is fall planting worth it in Colorado?
Absolutely. Many crops like broccoli, lettuce, and carrots taste sweeter when matured in cool fall weather. You’ll also deal with fewer pests than in the summer.
What are the best resources for Colorado gardeners?
Colorado State University Extension is the gold standard. They provide free, science-based fact sheets on every gardening topic imaginable, tailored specifically to our climate and soils. Their PlantTalk website is incredibly helpful.
Successfully timing your garden in Colorado is about observation and a little patience. Start with the calendar guidelines, but always let current weather and soil conditions have the final say. Keep a simple garden journal each year noting what you planted when and how it performed. This personal record will become your most valuable tool, helping you refine your timing for even better success every season. With this knowledge, you’re well on your way to a bountiful Colorado garden.