When to plant Geraniums in Arapahoe County, CO
In Arapahoe County, Geraniums is a single-season spring crop — there's no second fall window. Plant May 17–May 31 for an 70–100-day harvest, finishing well before the October 7 first frost.
When to Plant Geraniums in Arapahoe County, CO
This month in Arapahoe County, Colorado
June rewards gardeners who work with the weather, not against it. Here's how to stay in step this month in Arapahoe County, Colorado.
Get ahead of July
- Starting indoors: geraniums
- First harvests: geraniums
Geraniums (Pelargonium × hortorum) are tender perennials grown as warm-season annuals throughout North America. Prized for their bold flower clusters, long bloom period, and tolerance of summer heat when planted in well-drained soil, they anchor window boxes, containers, and bed borders from late spring until hard frost. Zones 9b–11b can overwinter plants in the ground.
Arapahoe County, Colorado is in USDA Zone 6a. The average last spring frost is May 10 and the first fall frost is October 7, giving you a growing season of approximately 150 days.
At an elevation of 7,205 feet, Arapahoe County receives approximately 21.4 inches of rainfall annually with predominantly loam soil. Summer highs average 87°F, providing good warmth for Geraniums during the growing season.
Arapahoe County Soil Profile
Soil Type
Loam
Soil pH
6.2-8.3
Drainage
Well Drained
Geraniums Planting Risk Windows
Percentages indicate frost risk at transplant. The 70% safe window means there is a 30% chance of frost after transplant — suitable for cold-hardy crops or gardeners with frost protection. The 90% safe window is best for tender plants.
Soil Compatibility in Arapahoe County
How your county's soil matches Geraniums's growing requirements.
Soil pH
Your soil pH (6.2–8.3) is more alkaline than Geraniums prefers (6.0–7.0). Add sulfur or peat moss to lower pH.
Soil Texture
The loam soil in Arapahoe County is excellent for Geraniums — good drainage, moisture retention, and nutrient holding capacity.
Organic Matter
Organic matter is moderate (2.5%). Annual compost additions will help Geraniums.
How to Plant Geraniums
Succession Planting Geraniums
Sow every 8 weeks. Last sowing by Jun 29 to harvest before frost.
Geraniums Water Budget
Water stress score is 8/10 — consider drought-tolerant varieties and mulching
Monthly Watering Guide for Geraniums
Geraniums needs approximately 1 inches of water per week (4.3" per month). Here's how your county's rainfall compares month by month.
| Month | Geraniums Needs | Rainfall | You Supplement | Action |
|---|---|---|---|---|
| Jan | — | 1.3" | 0" | ❄️ Dormant |
| Feb | — | 1.2" | 0" | ❄️ Dormant |
| Mar | — | 1.8" | 0" | ❄️ Dormant |
| Apr | — | 2.2" | 0" | ❄️ Dormant |
| May | 4.3" | 2.5" | 1.8" | 💧 Light watering |
| Jun | 4.3" | 1.4" | 2.9" | 🚿 Regular watering |
| Jul | 4.3" | 2" | 2.3" | 🚿 Regular watering |
| Aug | 4.3" | 2.4" | 1.9" | 💧 Light watering |
| Sep | 4.3" | 1.9" | 2.4" | 🚿 Regular watering |
| Oct | 4.3" | 1.7" | 2.6" | 🚿 Regular watering |
| Nov | — | 1.5" | 0" | ❄️ Dormant |
| Dec | — | 1.3" | 0" | ❄️ Dormant |
Water needs are for active growing months only (May–Oct in Arapahoe County). Supplement amounts are based on average rainfall — actual needs vary with temperature, soil, and mulching.
Geraniums Heat Requirements (GDD)
What are Growing Degree Days (GDD)?
Growing Degree Days measure the total warmth your plants receive during the growing season. Think of it as a "heat bank" — every day above 50°F deposits warmth that helps your plants grow.
Each plant needs a certain amount of accumulated heat to mature. If your county provides more GDD than the plant needs, it's a great fit. If it's close, you may want to choose faster-maturing varieties or start seeds indoors to get a head start.
Geraniums Planting Timeline — Arapahoe County, CO
Geraniums Planting Calendar
| Activity | When | Date Range |
|---|---|---|
| Start Indoors | March 1 | Mar 1 – Mar 15 |
| Transplant Outdoors | May 17 | May 17 – May 31 |
| Bloom | July 26 | Jul 26 – Oct 25 |
Plant 0.1" deep · 12" apart · Rows 14" apart
Month-by-Month Timeline
| Month | Activities |
|---|---|
| January | — |
| February | — |
| March | Start Indoors |
| April | — |
| May | Transplant Outdoors |
| June | — |
| July | Bloom |
| August | Bloom |
| September | Bloom |
| October | Bloom |
| November | — |
| December | — |
Growing Conditions
☀️ Sun
Full Sun (6-8+ hours)
💧 Water
1"/week · 1-2 times/week
📅 Days to Maturity
70–100 days
🧪 Soil pH
Needs 6–7 · Your soil: too_alkaline
🗺️ USDA Zone
Zone 6a
📆 Growing Season
150 days in Arapahoe County
Growing Tips for Geraniums in Arapahoe County
Direct sow Geraniums outdoors after May 10 in Arapahoe County when soil has warmed and frost danger has passed.
Arapahoe County receives only 21" of rain annually. Geraniums needs consistent moisture — install drip irrigation or water deeply 2-3 times per week.
General growing tips
Start seeds indoors 10–12 weeks before last frost — germination is slow and erratic without bottom heat (70–75°F). Transplant after frost danger passes. Geraniums rarely direct-sown; cuttings or transplants are the standard. Deadhead spent umbels weekly to maintain continuous bloom. Let soil dry slightly between waterings to prevent root rot. In zones 10–11 plants may be left in ground year-round or overwintered as houseplants.
Companion Planting
Good Companions
Check more plant combinations with our Companion Planting Checker →
Geraniums in Other Locations
Frequently Asked Questions
When should I plant Geraniums in Arapahoe County, CO?
Arapahoe County is in Zone 6a with an average last frost of May 10. Plan your Geraniums planting based on this frost date — see the calendar above for exact timing.
What planting zone is Arapahoe County, CO?
Arapahoe County, Colorado is in USDA Hardiness Zone 6a. The average last spring frost is May 10 and first fall frost is October 7.
When should I plant Geraniums in Arapahoe County, CO?
In Arapahoe County, CO, plant Geraniums after the last frost (around May 10) and before the first frost (around October 7). Best results when soil holds above 50°F.
What growing zone is Arapahoe County, CO for Geraniums?
Arapahoe County sits in USDA Zone 6a. Geraniums grows reliably in zones 2a through 11b, so it's a good fit here.
Can Geraniums grow in Arapahoe County's climate?
Yes — Geraniums grows well in Arapahoe County's temperate climate. Arapahoe County averages a 150-day frost-free season, with last frost around May 10 and first frost around October 7.
Your Arapahoe County Garden Planner — Free
A 22-page printable planner built for Arapahoe 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.