If you’re wondering when to plant herbs in Colorado, timing is everything for a successful garden. The state’s unique climate, with its late springs, early falls, and intense sun, means you need a smart plan. Getting your planting schedule right is the key to growing lush, flavorful herbs right outside your door.
This guide will walk you through the best planting times for both annual and perennial herbs in Colorado. We’ll cover everything from understanding your local frost dates to tips for extending your harvest season. Let’s get your herb garden started.
When to Plant Herbs in Colorado – Best Planting Times for
Colorado’s planting calendar revolves around one critical factor: the last and first frost dates. The average last spring frost can range from early May in Denver to mid-June in mountain towns. The first fall frost often arrives by early October, or even September at higher elevations.
You must know your specific dates. Check with your local extension office or use a reliable online garden calculator. Mark these dates on your calendar—they are your garden’s start and finish lines.
Understanding Your Colorado Growing Zone
Colorado spans USDA Hardiness Zones 3 through 7. This huge range affects what you can grow and when.
- Zones 5-7 (Front Range, Denver, Colorado Springs): Longer growing season. Last frost typically mid-to-late May.
- Zones 3-4 (High Mountain Valleys, San Luis Valley): Shorter, cooler season. Last frost can be early to mid-June. Choose cold-hardy herbs.
Always select herbs rated for your zone or one zone colder for better survival. This is a common mistake new gardeners make.
Planting Tender Annual Herbs (After Last Frost)
These herbs are frost-sensitive and must be planted outdoors only after all danger of frost has passed. They thrive in warm soil and air.
- Examples: Basil, cilantro, dill, parsley (often grown as an annual), lemongrass.
- Best Planting Time: Late May to early June. Wait for consistent nighttime temps above 50°F.
- Tip: You can start seeds indoors 6-8 weeks before your last frost date to get a head start. Transplant seedlings carefully.
Planting Hardy Perennial & Biennial Herbs (Early Spring or Fall)
These tough herbs survive Colorado winters and can be planted in early spring, as soon as the ground is workable, or in early fall.
- Examples: Sage, thyme, oregano, mint, chives, lavender, tarragon.
- Spring Planting: April to early May. This gives roots time to establish before summer heat.
- Fall Planting: Early September to early October. At least 6 weeks before the first hard freeze allows for root growth.
Perennials planted in fall often establish stronger roots and boom the following spring. Make sure to water them well until the ground freezes.
Using Season Extension Techniques
Colorado’s short season makes tools like these invaluble.
- Cold Frames & Row Covers: Protect early-planted herbs from late frosts and extend harvests into fall.
- Containers: Grow tender herbs in pots. Bring them indoors before the first fall frost to keep them producing.
- Wall of Waters or Cloches: Use these to plant warm-season herbs like basil 2-3 weeks earlier than normal.
A Month-by-Month Herb Planting Guide for Colorado
March – April: The Planning & Early Start
Indoors is where the action is. Start seeds of slow-growing herbs like oregano, thyme, and sage. In late April, if the soil isn’t soggy, you can plant bare-root perennial herbs or divide existing ones. Harden off indoor seedlings by slowly exposing them to outdoor conditions.
May: The Transition Month
This is a busy time. Early May, plant hardy perennial starts. After Mother’s Day, watch the forecast closely. Once frost danger is minimal, transplant your tender herb seedlings. Direct sow seeds of cilantro and dill for successive harvests.
June – July: Full Swing Planting
The soil is warm and ideal for planting any remaining herbs. This is also the time for succession planting. Sow another round of cilantro or dill every 3 weeks for a continuous supply. Keep new plantings well-watered during summer heat.
August – September: Prep for Fall
In early August, plant one last batch of fast-growing herbs like cilantro for a fall harvest. Early September is perfect for planting new perennial herbs or dividing old ones. Begin harvesting and preserving your abundance of herbs.
October – November: The Season’s End
Before the first hard freeze, harvest remaining tender herbs. Cut back most perennials, leaving some stems for winter interest and wildlife. Mulch heavily around the base of perennial herbs after the ground freezes to prevent frost heave.
Step-by-Step: Planting Herbs for Success
- Choose the Right Spot: Most herbs need 6+ hours of full sun. Well-draining soil is non-negotiable in Colorado’s heavy clay. Consider raised beds.
- Amend the Soil: Mix in 2-3 inches of compost or well-rotted manure to improve drainage and fertility. Colorado soil often needs organic matter.
- Plant at the Correct Depth: Set transplants at the same depth they were in their pot. For seeds, follow packet instructions—don’t plant to deep.
- Water Wisely: Water deeply immediately after planting. Then, let soil dry slightly between waterings. Herbs generally prefer less frequent, deep watering.
- Mulch: Apply a thin layer of organic mulch (like straw) to conserve moisture and suppress weeds. Keep it away from plant stems.
Common Mistakes to Avoid
- Planting Too Early: Impatience leads to frost damage. Heed frost dates.
- Overwatering: Herbs like thyme and lavender hate wet feet. Good drainage prevents root rot.
- Ignoring Sun Needs: Planting sun-lovers in shade results in leggy, weak plants with little flavor.
- Forgetting to Harden Off: Moving indoor seedlings directly outside shocks them. Always harden off over 7-10 days.
FAQ: Your Colorado Herb Planting Questions
What is the easiest herb to grow in Colorado?
Chives, thyme, oregano, and mint are incredibly resilient. They handle temperature swings, lower water, and poor soil better than many other herbs.
Can I grow herbs in Colorado all year?
Outdoors, no. But you can bring containers of basil, rosemary, or parsley indoors before frost. Place them in a sunny south-facing window to keep harvesting through winter.
When should I start herb seeds indoors in Colorado?
Start seeds for slow-growing perennials (lavender, sage) 10-12 weeks before last frost. Start tender annuals (basil) 6-8 weeks before. Don’t start to early or seedlings get leggy.
Is it better to plant herbs from seeds or starts?
For beginners, starts (small plants) are easier and give you a faster harvest. Seeds are more economical for herbs like cilantro and dill that don’t transplant as well.
How do I protect my herbs from a late spring frost?
Have old sheets, frost cloth, or cardboard boxes ready to cover tender plants overnight. Remove covers in the morning once temperatures rise. Watering the soil before a frost can also help, as moist soil retains heat better.
Growing herbs in Colorado is deeply rewarding once you sync with the rhythm of the seasons. By paying close attention to frost dates, choosing the right herbs for your zone, and using simple season extenders, you’ll enjoy fresh flavors from your garden for many months. Remember, gardening is a learning process—each season teaches you more about your unique patch of Colorado soil.