When to plant Hydrangeas in Lemhi County, ID
In Lemhi County, Hydrangeas is a spring-only crop. Plant June 23–July 7 once soil hits 50°F.
When to Plant Hydrangeas in Lemhi County, ID
Lemhi County, Idaho gardeners: here's your July plan
We've pulled the most time-sensitive tasks for Lemhi County, Idaho this July and put them front and centre. Tackle them in order.
Get ahead of August
- Starting indoors: hydrangeas
Hydrangeas (Hydrangea spp.) are among the most spectacular summer-blooming shrubs, with large mophead, lacecap, or panicle flower clusters lasting weeks in the garden and drying beautifully for arrangements. Native to Asia and North America alike, the genus spans several garden species with different hardiness and blooming habits. Panicle hydrangeas (H. paniculata, e.g., Limelight) are the most cold-hardy (Zone 3) and most reliable bloomers; smooth hydrangeas (H. arborescens, e.g., Annabelle) are equally tough. Bigleaf hydrangeas (H. macrophylla) are prized for blue/pink color-shifting blooms but require reliable snow cover or winter protection in Zones 5–6. Flower color in macrophylla types is determined by soil pH (acidic = blue, alkaline = pink).
Lemhi County, Idaho is in USDA Zone 5b. The average last spring frost is June 9 and the first fall frost is September 14, giving you a growing season of approximately 97 days.
At an elevation of 6,743 feet, Lemhi County receives approximately 12.6 inches of rainfall annually with predominantly loam soil. Summer highs average 84°F, so choose short-season varieties of Hydrangeas to ensure they mature before fall. With low rainfall, drip irrigation is essential for growing Hydrangeas successfully. Mulch heavily to conserve soil moisture.
Lemhi County Soil Profile
Soil Type
Loam
Soil pH
6.2-8.2
Drainage
Well Drained
Hydrangeas 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 Lemhi County
How your county's soil matches Hydrangeas's growing requirements.
Soil pH
Your soil pH (6.2–8.2) is more alkaline than Hydrangeas prefers (5.5–6.5). Add sulfur or peat moss to lower pH.
Soil Texture
The loam soil in Lemhi County is excellent for Hydrangeas — good drainage, moisture retention, and nutrient holding capacity.
Organic Matter
Organic matter is moderate (2.8%). Annual compost additions will help Hydrangeas.
How to Plant Hydrangeas
Hydrangeas Water Budget
Water stress score is 6/10 — consider drought-tolerant varieties and mulching
Monthly Watering Guide for Hydrangeas
Hydrangeas needs approximately 1 inches of water per week (4.3" per month). Here's how your county's rainfall compares month by month.
| Month | Hydrangeas Needs | Rainfall | You Supplement | Action |
|---|---|---|---|---|
| Jan | — | 0.8" | 0" | ❄️ Dormant |
| Feb | — | 0.9" | 0" | ❄️ Dormant |
| Mar | — | 1" | 0" | ❄️ Dormant |
| Apr | — | 1.3" | 0" | ❄️ Dormant |
| May | — | 1.4" | 0" | ❄️ Dormant |
| Jun | 4.3" | 0.8" | 3.5" | 🚿 Regular watering |
| Jul | 4.3" | 1.3" | 3" | 🚿 Regular watering |
| Aug | 4.3" | 1.3" | 3" | 🚿 Regular watering |
| Sep | 4.3" | 1.2" | 3.1" | 🚿 Regular watering |
| Oct | — | 1" | 0" | ❄️ Dormant |
| Nov | — | 1" | 0" | ❄️ Dormant |
| Dec | — | 0.8" | 0" | ❄️ Dormant |
Water needs are for active growing months only (Jun–Sep in Lemhi County). Supplement amounts are based on average rainfall — actual needs vary with temperature, soil, and mulching.
Hydrangeas 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.
Hydrangeas Planting Timeline — Lemhi County, ID
Hydrangeas Planting Calendar
| Activity | When | Date Range |
|---|---|---|
| Start Indoors | March 31 | Mar 31 – Apr 14 |
| Transplant Outdoors | June 23 | Jun 23 – Jul 7 |
| Bloom | September 8 | Sep 8 – Dec 1 |
Plant 1" deep · 48" apart · Rows 60" apart
Month-by-Month Timeline
| Month | Activities |
|---|---|
| January | — |
| February | — |
| March | Start Indoors |
| April | Start Indoors |
| May | — |
| June | Transplant Outdoors |
| July | Transplant Outdoors |
| August | — |
| September | Bloom |
| October | Bloom |
| November | Bloom |
| December | Bloom |
Growing Conditions
☀️ Sun
Partial Shade (3-6 hours)
💧 Water
1"/week · 1-2 times/week
📅 Days to Maturity
90–150 days
🧪 Soil pH
Needs 5.5–6.5 · Your soil: too_alkaline
🗺️ USDA Zone
Zone 5b
📆 Growing Season
97 days in Lemhi County
Growing Tips for Hydrangeas in Lemhi County
Direct sow Hydrangeas outdoors after June 09 in Lemhi County when soil has warmed and frost danger has passed.
Your 97.0-day growing season in Lemhi County is tight for Hydrangeas (90.0-150.0 days to maturity). Start indoors and choose early-maturing varieties.
Lemhi County receives only 13" of rain annually. Hydrangeas needs consistent moisture — install drip irrigation or water deeply 2-3 times per week.
General growing tips
Plant container-grown specimens in spring or fall, spacing at least 3–5 feet apart to allow for mature shrub spread. Most hydrangeas prefer morning sun with afternoon shade, especially in Zones 7+. Keep consistently moist — the name derives from the Greek for water vessel. Prune panicle and smooth types in late winter/early spring (they bloom on new wood). Prune bigleaf types only lightly after bloom; cutting stems in fall removes next year's buds. In Zone 5–6, protect bigleaf varieties with burlap or wire cages filled with leaves over winter. Fall planting (Zones 5+) gives excellent root establishment before summer heat. Year 2+ plants reach full size and bloom.
Companion Planting
Good Companions
Check more plant combinations with our Companion Planting Checker →
Hydrangeas in Other Locations
Frequently Asked Questions
When should I plant Hydrangeas in Lemhi County, ID?
Lemhi County is in Zone 5b with an average last frost of June 9. Plan your Hydrangeas planting based on this frost date — see the calendar above for exact timing.
What planting zone is Lemhi County, ID?
Lemhi County, Idaho is in USDA Hardiness Zone 5b. The average last spring frost is June 9 and first fall frost is September 14.
When should I plant Hydrangeas in Lemhi County, ID?
In Lemhi County, ID, plant Hydrangeas after the last frost (around June 9) and before the first frost (around September 14). Best results when soil holds above 50°F.
What growing zone is Lemhi County, ID for Hydrangeas?
Lemhi County sits in USDA Zone 5b. Hydrangeas grows reliably in zones 3a through 9a, so it's a good fit here.
Can Hydrangeas grow in Lemhi County's climate?
Yes — Hydrangeas grows well in Lemhi County's temperate climate. Lemhi County averages a 97-day frost-free season, with last frost around June 9 and first frost around September 14.
Your Lemhi County Garden Planner — Free
A 22-page printable planner built for Lemhi County (Zone 5b). Planting dates, a month-by-month schedule, harvest log, seed inventory, and succession charts — all dialed in for your exact growing season.