Colorado’s high altitude and dry air call for larkspur seeds to be planted in early spring after the snow melts. Knowing the best time to plant larkspur in Colorado is the key to getting those tall, colorful spikes to bloom in your mountain garden. Larkspur (a type of delphinium) loves cool weather, so timing is everything here.
If you plant too early, a late frost might kill the seedlings. Plant too late, and the summer heat will stress them out before they even get started. This guide walks you through exactly when and how to plant larkspur seeds in Colorado, whether you live in Denver, Colorado Springs, or up in the mountains.
Why Timing Matters For Larkspur In Colorado
Colorado’s growing season is short and unpredictable. The soil can stay frozen well into April in some areas. Larkspur seeds actually need a cold period (stratification) to germinate well. That’s why fall planting or very early spring planting works best.
In the wild, larkspur seeds drop in late summer, sit through winter, and sprout when the snow melts. You want to mimic that natural cycle. The best time to plant larkspur in Colorado is when the ground is workable but still cool, usually between late March and mid-May, depending on your elevation.
How Elevation Changes Your Planting Window
Colorado’s elevation ranges from about 5,000 feet in Denver to over 8,000 feet in the mountains. This changes everything.
- Front Range (5,000-6,000 ft): Plant seeds from mid-March to mid-April. Snow usually melts by late March.
- Foothills (6,000-7,500 ft): Wait until early April to early May. Soil takes longer to warm up.
- High Mountains (7,500+ ft): Plant from late April to late May. Snow can linger into May.
Check your local frost dates. In Denver, the last frost is usually around May 5. In the mountains, it can be June 1 or later. Larkspur can handle light frost, but hard freezes (below 28°F) will kill young plants.
Best Time To Plant Larkspur In Colorado
Now let’s get specific. The exact best time to plant larkspur in Colorado is early spring, as soon as the soil is thawed and you can dig without it being muddy. For most Colorado gardeners, that means late March through early May.
Here’s a simple rule: plant larkspur seeds when the soil temperature is between 45°F and 55°F. Use a soil thermometer to check. If the soil is still frozen or too wet, wait a week.
Fall Planting Option
Some gardeners prefer to plant larkspur seeds in fall, around October or November. The seeds sit dormant over winter and sprout naturally in spring. This works great for native larkspur species, but it’s riskier for hybrid varieties. Mice and birds might eat the seeds over winter.
If you try fall planting, sow seeds after the first hard frost but before the ground freezes solid. This is usually late October in Denver, earlier in the mountains.
Spring Planting Step-By-Step
- Prepare the soil: Larkspur likes well-draining soil with compost mixed in. Remove rocks and weeds.
- Sow seeds: Scatter seeds on the surface, then cover with about 1/8 inch of soil. Larkspur needs light to germinate, so don’t bury them deep.
- Water gently: Use a fine spray so you don’t wash seeds away. Keep the soil moist but not soggy.
- Thin seedlings: Once they sprout (in 2-3 weeks), thin to 12-18 inches apart. Crowded plants get powdery mildew.
- Mulch lightly: A thin layer of straw or shredded leaves helps keep soil cool and moist.
Understanding Colorado’s Climate Challenges
Colorado’s weather is famous for being bipolar. You might get a 70°F day in March followed by a snowstorm the next week. Larkspur can handle some cold, but sudden temperature swings stress them out.
Here are the main challenges you’ll face:
- Late frosts: Protect young seedlings with row covers or cloches if a freeze is predicted.
- Dry air: Colorado’s humidity is often below 30%. Larkspur likes consistent moisture, so water deeply once a week.
- Intense sun: At high altitude, UV rays are stronger. Plant larkspur where they get morning sun and afternoon shade.
- Wind: Larkspur stalks can grow 3-4 feet tall and snap in strong winds. Stake them early.
Soil Preparation Tips For Colorado
Colorado soil is often clay-heavy or sandy. Neither is ideal for larkspur. Clay holds too much water and can rot roots. Sand drains too fast and dries out.
Amend your soil with organic matter like compost or aged manure. Aim for a loamy texture. Larkspur prefers a neutral to slightly alkaline pH (6.5-7.5). Colorado soil is usually alkaline, so you might not need to adjust it.
If you’re planting in a raised bed, use a mix of garden soil, compost, and perlite for drainage.
Varieties Of Larkspur That Thrive In Colorado
Not all larkspur varieties are created equal. Some handle Colorado’s conditions better than others.
- Consolida ajacis (annual larkspur): These are the classic tall spikes in blue, pink, white, and purple. They bloom in early summer and self-seed easily.
- Delphinium elatum (perennial larkspur): These are true delphiniums. They’re more finicky but come back year after year. They need winter protection in cold areas.
- Native larkspur (Delphinium nuttallianum): This wildflower grows naturally in Colorado meadows. It’s very hardy and drought-tolerant once established.
For beginners, annual larkspur is the easiest. Just plant seeds in spring and enjoy blooms by June or July.
Where To Buy Larkspur Seeds In Colorado
Local nurseries often carry varieties that are adapted to Colorado. Big-box stores might sell seeds that are meant for milder climates. Look for seed packets that mention “cold hardy” or “mountain grown.”
Online sources like High Country Gardens or Botanical Interests (based in Colorado) are reliable. They know what works here.
Caring For Larkspur After Planting
Once your larkspur seeds are in the ground, the real work begins. Here’s how to keep them happy through Colorado’s wild spring and summer.
Watering
Larkspur needs consistent moisture, especially during germination and early growth. Water deeply once a week, more often if it’s hot and dry. Avoid overhead watering, which can cause powdery mildew. Use a soaker hose or drip irrigation.
In Colorado’s dry climate, you might need to water every 3-4 days during heat waves. Check the soil 1 inch down. If it’s dry, water.
Fertilizing
Larkspur isn’t a heavy feeder, but a little fertilizer helps. Apply a balanced, slow-release fertilizer (10-10-10) when the seedlings are 4 inches tall. Avoid high-nitrogen fertilizers, which produce lots of leaves but few flowers.
If your soil is rich in compost, you might not need fertilizer at all.
Staking
Tall larkspur varieties need support. Insert stakes or a peony ring when the plants are 12 inches tall. Do this early so you don’t damage the roots later. Use soft ties to secure the stalks.
In windy Colorado, staking is non-negotiable. A sudden thunderstorm can flatten an entire bed of larkspur.
Deadheading
Remove spent flowers to encourage more blooms. Cut the flower spike down to a leaf node. If you want the plant to self-seed, leave a few flowers to go to seed in late summer.
Common Problems With Larkspur In Colorado
Even with perfect timing, larkspur can run into issues. Here are the most common ones and how to fix them.
- Powdery mildew: This white fungus appears on leaves in humid conditions. Space plants well and water at the base. Remove infected leaves.
- Slugs and snails: These pests love larkspur. Use beer traps or diatomaceous earth around the plants.
- Aphids: Small green bugs that suck sap. Spray them off with water or use insecticidal soap.
- Root rot: Caused by overwatering or heavy clay soil. Improve drainage and water less frequently.
- Deer and rabbits: Larkspur is toxic to many animals, but deer might still nibble it. Use fencing or repellents.
Powdery Mildew Prevention
Powdery mildew is the biggest problem for larkspur in Colorado. The dry air doesn’t stop it if plants are crowded or watered from above.
Prevent it by:
- Planting in full sun with good air circulation
- Watering at the soil level, not on leaves
- Thinning seedlings to 18 inches apart
- Applying a sulfur-based fungicide if you see early signs
Extending The Bloom Season
Larkspur blooms for about 3-4 weeks in early summer. To enjoy them longer, try succession planting.
Sow a batch of seeds in early April, another in late April, and a third in mid-May. Each batch will bloom a few weeks apart. This works best with annual larkspur, which matures faster than perennials.
You can also mix early-blooming and late-blooming varieties. Check seed packets for “days to bloom” information.
Companion Plants For Larkspur
Larkspur looks great with other cool-season flowers. Try planting them with:
- Poppies (they bloom around the same time)
- Bachelor’s buttons
- Cosmos
- Snapdragons
- Dianthus
These plants have similar water and sun needs. They also attract pollinators like bees and butterflies.
Overwintering Perennial Larkspur
If you planted perennial larkspur (Delphinium), you need to protect it through Colorado’s harsh winters. Mulch heavily with straw or leaves after the ground freezes. This insulates the roots from freeze-thaw cycles.
In spring, remove the mulch gradually as the soil warms. Don’t uncover too early, or a late frost might kill the new growth.
Perennial larkspur often needs to be divided every 3-4 years to stay healthy. Do this in early spring or fall.
Frequently Asked Questions
Can I Plant Larkspur Seeds Directly In The Ground In Colorado?
Yes, direct sowing is the best method. Larkspur has a taproot that doesn’t transplant well. Just make sure the soil is workable and not frozen.
What Is The Best Month To Plant Larkspur In Denver?
For Denver, aim for mid-March to mid-April. The soil is usually thawed by then, and the risk of heavy snow is lower.
Do Larkspur Come Back Every Year In Colorado?
Annual larkspur (Consolida) does not come back, but it self-seeds readily. Perennial larkspur (Delphinium) can come back for several years with proper care.
How Deep Should I Plant Larkspur Seeds?
Cover seeds with only 1/8 inch of soil. They need light to germinate. Press them gently into the soil surface.
Can Larkspur Grow In Pots In Colorado?
Yes, but use deep pots (at least 12 inches) to accommodate the taproot. Keep pots in a sheltered spot to protect from wind and intense sun.
Final Tips For Success
Planting larkspur in Colorado is all about timing and patience. Start with the best time to plant larkspur in Colorado, which is early spring after the snow melts. Prepare your soil well, water consistently, and protect your plants from wind and late frosts.
Don’t be afraid to experiment. Try planting a few seeds in fall and a few in spring to see what works best in your microclimate. Larkspur is forgiving once it’s established, and the reward is those stunning flower spikes that make Colorado gardens look magical.
Remember that larkspur is toxic if ingested, so keep it away from pets and children. Wear gloves when handling the plants, especially if you have sensitive skin.
With the right timing and care, you’ll have a beautiful display of larkspur that will make your neighbors jealous. Happy planting!