Knowing when to plant flowers in Colorado is the key to a successful and vibrant garden. Our unique climate, with its late frosts, intense sun, and variable weather, makes timing everything. Get it right, and your garden will thrive. Get it wrong, and you might face disappointment. This guide will walk you through the optimal schedule for planting flowers across the state.
We’ll break it down by season, flower type, and even your specific Colorado hardiness zone. You’ll learn how to work with our environment, not against it. Let’s get started with the most important factor of all: your last spring frost date.
When To Plant Flowers In Colorado
This heading is your golden rule. The average last spring frost date is your starting point for all planting. Colorado’s dates vary dramatically from early May in Denver to mid-June in mountain towns. You must know your local date. Check with your county extension office or use a reliable online frost date calculator for your zip code.
Understanding Colorado’s Planting Zones
Colorado spans USDA hardiness zones 3 through 7. This range means a plant that’s perennial in Pueblo might be an annual in Fort Collins. Always check a plant’s zone rating before buying.
- Zones 5-7 (Front Range, Denver, Colorado Springs, Pueblo): Longer growing season, warmer winters. Last frost typically early to mid-May.
- Zones 3-4 (High Plains, Mountain Valleys, High-Altitude Areas): Shorter season, colder winters. Last frost can be early to mid-June. Frost can occur even in summer.
Spring Planting: The Main Event
Spring is the busiest planting time. The goal is to get plants in after the frost danger passes but before the summer heat arrives.
Hardy Annuals & Perennials
These tough flowers can handle a light frost and cooler soil. You can plant them 2-4 weeks before your last frost date. They often establish better in the cool weather.
- Pansies
- Violas
- Snapdragons
- Dianthus
- Certain native wildflower seeds
Tender Annuals & Summer Bulbs
These are the heat-lovers that will die in a frost. You must wait until all danger of frost has completely passed. This is usually 1-2 weeks after your last frost date. Patience is crucial here.
- Petunias, Geraniums, Impatiens
- Marigolds, Zinnias, Sunflowers
- Dahlias, Gladiolus, Cannas
Fall Planting: A Secret Advantage
Fall is an excellent, often overlooked, time for planting in Colorado. The soil is warm, the air is cool, and autumn rains provide natural irrigation. This gives perennials, bulbs, and wildflowers a head start for spring.
Planting Perennials in Fall
Aim to plant at least 6 weeks before the first hard freeze. This allows roots to establish in the warm soil before winter dormancy. Be sure to water them deeply until the ground freezes.
Spring-Blooming Bulbs
Tulips, daffodils, crocus, and alliums must be planted in fall. They need a long period of cold winter temperatures to bloom properly. Plant them from late September through October, before the ground freezes solid.
A Seasonal Planting Calendar for Colorado
Here’s a quick-reference timeline. Adjust based on your exact zone and current year’s weather patterns.
March – April
- Start seeds indoors for tender annuals (like zinnias and tomatoes).
- Direct sow hardy annual seeds (like poppies) as soon as soil is workable.
- Divide and transplant overgrown perennials as they emerge.
May – Early June
- After last frost, plant tender annuals and summer bulbs.
- Transplant your indoor-started seedlings.
- Plant container-grown perennials.
- Begin regular watering as temperatures rise.
Late August – September
- Plant new perennials and ornamental grasses.
- Divide and replant existing perennials that bloom in spring or summer.
- Order spring-blooming bulbs for fall planting.
October – November
- Plant spring-blooming bulbs.
- Apply a final deep watering to all plants before winter.
- Mulch newly planted perennials and bulbs after the ground gets cold.
Step-by-Step: How to Plant for Success
Proper planting technique is as important as timing. Follow these steps to give your flowers the best start.
- Amend the Soil: Colorado soil is often clay-heavy or sandy. Mix in 3-4 inches of quality compost to improve drainage and nutrients.
- Dig the Right Hole: For pots, dig a hole twice as wide as the root ball but no deeper. The plant should sit at the same level it was in its container.
- Water Deeply: Water the hole before placing the plant. Then, water thoroughly after planting to settle the soil.
- Mulch: Apply 2-3 inches of mulch (like wood chips) around plants. This retains moisture, suppresses weeds, and moderates soil temperature.
- Acclimate Seedlings: If you started plants indoors or bought them from a greenhouse, “harden them off” by gradually exposing them to outdoor conditions over 7-10 days.
Choosing the Right Flowers for Colorado
Selecting resilient plants is half the battle. Opt for varieties known for drought tolerance, sun-loving habits, and cold hardiness.
- Native Plants: Penstemon, Blanket Flower, Colorado Blue Columbine, and Bee Balm are adapted to our climate and support local wildlife.
- Drought-Tolerant Favorites: Lavender, Russian Sage, Sedum, Yarrow, and Coreopsis.
- Long-Blooming Annuals: Zinnias, Marigolds, and Cosmos provide reliable color all summer with minimal fuss.
FAQ: Planting Flowers in Colorado
What is the best month to plant flowers in Colorado?
For summer annuals, May is generally safest for the Front Range, while June is better for high altitudes. For perennials and bulbs, September and October are ideal months for fall planting.
Can I plant flowers before Mother’s Day in Colorado?
It’s risky. Mother’s Day is a common rule of thumb, but frosts can occur after. Always check your local last frost date. Only plant hardy varieties like pansies before that date.
How do I protect my flowers from a late spring frost?
Cover tender plants with frost cloth, old sheets, or cardboard boxes overnight. Avoid using plastic directly on foliage. Watering the soil around the plants before a frost can also help, as moist soil retains heat better.
Is it to late to plant wildflower seeds in June?
For many annual wildflowers, yes, it might be too late for blooms that same year. However, you can sow perennial wildflower seeds in fall for germination the following spring. They often need a cold period to break dormancy.
What flowers come back every year in Colorado?
Many perennials are reliable. Coneflower, Salvia, Daylily, Hostas (in shade), and Peonies are excellent choices. Always verify the zone hardiness matches your specific area’s winter lows.
Gardening in Colorado is a rewarding challenge that teaches patience and observation. By syncing your planting schedule with the state’s unique rhythms, you’ll create a beautiful, resilient garden that flourishes from spring to fall. Remember to keep a garden journal note your planting dates, what thrived, and what struggled. This personal record will be your most valuable tool for seasons to come.