When to Plant Zinnia in Union County, OR
Your June gardening checklist
Each item below is timed to Union County, Oregon's frost dates and soil temperatures. Skip nothing, stress about nothing.
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Get zinnia seeds going inside
A seed-starting mix and a sunny window (or a grow light) are all you need. Keep soil warm — around 70°F — for fast germination.
To set up a strong July, finish these tasks
- First harvests: zinnia
Zinnia (Zinnia elegans) is a fast-growing, heat-loving annual that produces bold, dahlia-like blooms from early summer until hard frost. One of the easiest flowers to grow from direct-sown seed, zinnias thrive in hot, dry conditions and are magnets for butterflies and beneficial insects. They make excellent companion plants alongside marigolds in the vegetable garden.
Union County, Oregon is in USDA Zone 6b. The average last spring frost is May 12 and the first fall frost is September 26, giving you a growing season of approximately 137 days.
At an elevation of 2,751 feet, Union County receives approximately 23.5 inches of rainfall annually with predominantly silt loam soil. Summer highs average 86°F, providing good warmth for Zinnia during the growing season.
Union County Soil Profile
Soil Type
Silt Loam
Soil pH
5.2-6.6
Drainage
Well Drained
Zinnia 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 Union County
How your county's soil matches Zinnia's growing requirements.
Soil pH
Your soil pH (5.2–6.6) overlaps with Zinnia's range (5.5–7.5), though not a perfect match.
Soil Texture
The silt loam soil in Union County is excellent for Zinnia — good drainage, moisture retention, and nutrient holding capacity.
Drainage
Drainage is adequate for Zinnia.
Organic Matter
Organic matter is excellent (5.6%) — Zinnia will thrive.
How to Plant Zinnia
Succession Planting Zinnia
Sow every 6.9 weeks. Last sowing by Jul 18 to harvest before frost.
Zinnia Water Budget
Monthly Watering Guide for Zinnia
Zinnia needs approximately 0.5 inches of water per week (2.2" per month). Here's how your county's rainfall compares month by month.
| Month | Zinnia Needs | Rainfall | You Supplement | Action |
|---|---|---|---|---|
| Jan | — | 2.9" | 0" | ❄️ Dormant |
| Feb | — | 2.6" | 0" | ❄️ Dormant |
| Mar | — | 2.3" | 0" | ❄️ Dormant |
| Apr | — | 1.5" | 0" | ❄️ Dormant |
| May | 2.2" | 1.5" | 0.7" | 💧 Light watering |
| Jun | 2.2" | 0.9" | 1.3" | 🚿 Regular watering |
| Jul | 2.2" | 0.4" | 1.8" | 🚿 Regular watering |
| Aug | 2.2" | 0.5" | 1.7" | 🚿 Regular watering |
| Sep | 2.2" | 1" | 1.2" | 🚿 Regular watering |
| Oct | — | 2" | 0" | ❄️ Dormant |
| Nov | — | 3.8" | 0" | ❄️ Dormant |
| Dec | — | 4.2" | 0" | ❄️ Dormant |
Water needs are for active growing months only (May–Sep in Union County). Supplement amounts are based on average rainfall — actual needs vary with temperature, soil, and mulching.
Zinnia 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.
Zinnia Planting Timeline — Union County, OR
Zinnia Planting Calendar
| Activity | When | Date Range |
|---|---|---|
| Start Indoors | April 14 | Apr 14 – Apr 28 |
| Transplant Outdoors | May 12 | May 12 – May 26 |
| Direct Sow | May 12 | May 12 – Jun 2 |
| Bloom | July 21 | Jul 21 – Oct 27 |
Plant 0.3" deep · 12" apart · Rows 18" apart
Month-by-Month Timeline
| Month | Activities |
|---|---|
| January | — |
| February | — |
| March | — |
| April | Start Indoors |
| May | Transplant Outdoors Direct Sow |
| June | Direct Sow |
| July | Bloom |
| August | Bloom |
| September | Bloom |
| October | Bloom |
| November | — |
| December | — |
Growing Conditions
☀️ Sun
Full Sun (6-8+ hours)
💧 Water
0.5"/week · Natural rainfall sufficient
📅 Days to Maturity
60–70 days
🧪 Soil pH
Needs 5.5–7.5 · Your soil: acceptable
🗺️ USDA Zone
Zone 6b
📆 Growing Season
137 days in Union County
Growing Tips for Zinnia in Union County
Direct sow Zinnia outdoors after May 12 in Union County when soil has warmed and frost danger has passed.
Common pests for Zinnia in this region include aphids and slugs. Use row covers early in the season and inspect plants weekly.
Union County receives only 24" of rain annually. Zinnia needs consistent moisture — install drip irrigation or water deeply 2-3 times per week.
General growing tips
Direct-sow after last frost when soil reaches 60°F; seeds germinate in 5-7 days. In zones 3-5 a brief indoor start (4 weeks) is worthwhile but transplant carefully — zinnias dislike root disturbance. Deadhead frequently to extend bloom. Excellent cut flower; harvesting regularly encourages branching. Avoid overhead watering to reduce powdery mildew.
Companion Planting
Good Companions
Avoid Planting Near
Check more plant combinations with our Companion Planting Checker →
Zinnia in Other Locations
Frequently Asked Questions
When should I plant Zinnia in Union County, OR?
Union County is in Zone 6b with an average last frost of May 12. Plan your Zinnia planting based on this frost date — see the calendar above for exact timing.
What planting zone is Union County, OR?
Union County, Oregon is in USDA Hardiness Zone 6b. The average last spring frost is May 12 and first fall frost is September 26.
Your Union County Garden Planner — Free
A 22-page printable planner built for Union County (Zone 6b). Planting dates, a month-by-month schedule, harvest log, seed inventory, and succession charts — all dialed in for your exact growing season.