When to plant Alliums in Summit County, CO
Summit County gardeners should plant Alliums between mid-spring and late spring in spring. With Summit County's Zone 5a climate (last frost June 16), Alliums needs 28–42 days to mature — plant by July 24 for a full harvest. A second sowing from July 24 to August 7 extends the harvest into fall.
When to Plant Alliums in Summit County, CO
Ornamental alliums (Allium spp.) bridge the gap between spring and summer with their striking globe-shaped flower heads in shades of purple, violet, white, and pink. Blooming after tulips have faded, they extend the spring display well into early summer. 'Gladiator', 'Globemaster', and 'Purple Sensation' produce softball-sized heads on 18–36 inch stems, while smaller species create charming accents at border fronts. Deer and rodents shun them completely due to the characteristic onion scent. Dried seed heads provide architectural interest into fall.
Summit County, Colorado is in USDA Zone 5a. The average last spring frost is June 16 and the first fall frost is September 4, giving you a growing season of approximately 80 days.
At an elevation of 7,005 feet, Summit County receives approximately 17.5 inches of rainfall annually with predominantly loam soil. Summer highs average 81°F, so choose short-season varieties of Alliums to ensure they mature before fall. With low rainfall, drip irrigation is essential for growing Alliums successfully. Mulch heavily to conserve soil moisture.
Summit County Soil Profile
Soil Type
Loam
Soil pH
6.0-7.0
Drainage
Well Drained
Alliums Planting Timeline — Summit County, CO
Alliums Planting Calendar
| Activity | When | Date Range |
|---|---|---|
| Bloom | August 28 | Aug 28 – Sep 25 |
| Fall Sowing | July 24 | Jul 24 – Aug 7 |
Plant 5" deep · 7" apart · Rows 8" apart
Month-by-Month Timeline
| Month | Activities |
|---|---|
| January | — |
| February | — |
| March | — |
| April | — |
| May | — |
| June | — |
| July | Fall Sowing |
| August | Fall Sowing Bloom |
| September | Bloom |
| October | — |
| November | — |
| December | — |
Growing Conditions
☀️ Sun
Full Sun (6-8+ hours)
💧 Water
Low — drought tolerant
📅 Days to Maturity
28–42 days
🧪 Soil pH
Needs 5.5–7.5 · Your soil: N/A
🗺️ USDA Zone
Zone 5a
📆 Growing Season
80 days in Summit County
Growing Tips for Summit County
Plant bulbs in fall, 3–4 times as deep as the bulb diameter (typically 4–6 inches for large types, 3 inches for small species). Space 6–8 inches apart for standard cultivars. Foliage often looks untidy as it dies back before bloom — plant around perennials that will conceal the yellowing leaves. Excellent drainage is essential; alliums rot in wet soils. Leave bulbs in place for naturalization; divide every 3–4 years when clusters become congested. Deadhead spent globes or leave for ornamental seedheads and self-sowing.
Companion Planting
Good Companions
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Alliums in Other Locations
Frequently Asked Questions
When should I plant Alliums in Summit County, CO?
Summit County is in Zone 5a with an average last frost of June 16. Plan your Alliums planting based on this frost date — see the calendar above for exact timing.
What planting zone is Summit County, CO?
Summit County, Colorado is in USDA Hardiness Zone 5a. The average last spring frost is June 16 and first fall frost is September 4.
When should I plant Alliums in Summit County, CO?
In Summit County, CO, plant Alliums after the last frost (around June 16) and before the first frost (around September 4). Best results when soil holds above 50°F.
What growing zone is Summit County, CO for Alliums?
Summit County sits in USDA Zone 5a. Alliums grows reliably in zones 3a through 9b, so it's a good fit here.
Can Alliums grow in Summit County's climate?
Yes — Alliums grows well in Summit County's temperate climate. Summit County averages a 80-day frost-free season, with last frost around June 16 and first frost around September 4.
Your Summit County Garden Planner — Free
A 22-page printable planner built for Summit County (Zone 5a). Planting dates, a month-by-month schedule, harvest log, seed inventory, and succession charts — all dialed in for your exact growing season.