When to plant Larkspur in Boulder County, CO
Boulder County sits in cold Zone 6a. Plant Larkspur April 16–May 7 for the single annual harvest; the September 26 first frost closes the window.
When to Plant Larkspur in Boulder County, CO
Larkspur (Consolida ajacis) is a cool-season annual that produces tall, delicate spires of blue, purple, pink, and white flowers reminiscent of its perennial cousin, delphinium. Direct-sown into cold soil or fall-sown in mild-winter climates, it blooms in spring before going to seed as summer heat arrives. An excellent cut flower and cottage-garden staple.
Boulder County, Colorado is in USDA Zone 6a. The average last spring frost is May 14 and the first fall frost is September 26, giving you a growing season of approximately 135 days.
At an elevation of 7,657 feet, Boulder County receives approximately 22.2 inches of rainfall annually with predominantly loam soil. Summer highs average 86°F, providing good warmth for Larkspur during the growing season.
Boulder County Soil Profile
Soil Type
Loam
Soil pH
6.0-7.0
Drainage
Well Drained
Larkspur Planting Timeline — Boulder County, CO
Larkspur Planting Calendar
| Activity | When | Date Range |
|---|---|---|
| Direct Sow | April 16 | Apr 16 – May 7 |
| Bloom | June 25 | Jun 25 – Aug 20 |
Plant 0.1" deep · 8" apart · Rows 12" apart
Month-by-Month Timeline
| Month | Activities |
|---|---|
| January | — |
| February | — |
| March | — |
| April | Direct Sow |
| May | Direct Sow |
| June | Bloom |
| July | Bloom |
| August | Bloom |
| September | — |
| October | — |
| November | — |
| December | — |
Growing Conditions
☀️ Sun
Full Sun (6-8+ hours)
💧 Water
Low — drought tolerant
📅 Days to Maturity
60–90 days
🧪 Soil pH
Needs 6–7 · Your soil: N/A
🗺️ USDA Zone
Zone 6a
📆 Growing Season
135 days in Boulder County
Growing Tips for Boulder County
Larkspur does not transplant well — direct-sow only. In cold climates (zones 2–6), sow directly in early spring as soon as soil can be worked, 4–6 weeks before last frost; cold soil improves germination. In zones 7–10, fall-sow 8–10 weeks before first frost for spring bloom. Press seeds lightly into soil; they need darkness to germinate — cover with 1/8–1/4 inch of soil. Thin to 6–12 inches to prevent powdery mildew. Allow seed pods to mature and self-sow for naturalized colonies. All parts are toxic if ingested.
Companion Planting
Good Companions
Check more plant combinations with our Companion Planting Checker →
Larkspur in Other Locations
Frequently Asked Questions
When should I plant Larkspur in Boulder County, CO?
Boulder County is in Zone 6a with an average last frost of May 14. Plan your Larkspur planting based on this frost date — see the calendar above for exact timing.
What planting zone is Boulder County, CO?
Boulder County, Colorado is in USDA Hardiness Zone 6a. The average last spring frost is May 14 and first fall frost is September 26.
When should I plant Larkspur in Boulder County, CO?
In Boulder County, CO, plant Larkspur after the last frost (around May 14) and before the first frost (around September 26). Best results when soil holds above 50°F.
What growing zone is Boulder County, CO for Larkspur?
Boulder County sits in USDA Zone 6a. Larkspur grows reliably in zones 2a through 10b, so it's a good fit here.
Can Larkspur grow in Boulder County's climate?
Yes — Larkspur grows well in Boulder County's temperate climate. Boulder County averages a 135-day frost-free season, with last frost around May 14 and first frost around September 26.
Your Boulder County Garden Planner — Free
A 22-page printable planner built for Boulder County (Zone 6a). Planting dates, a month-by-month schedule, harvest log, seed inventory, and succession charts — all dialed in for your exact growing season.