When to Plant Lavender in Boulder, UT
Garfield County, Utah gardeners: here's your August plan
Welcome to August in Zone 6a. These are the moves that will have the biggest impact on your growing season.
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Begin indoor sowing: lavender
You're about 7 weeks out from your last frost — the perfect window to get these germinating indoors.
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Start harvesting lavender
Don't tug. Use scissors or pruners for clean cuts — torn stems invite disease.
To set up a strong September, finish these tasks
- First harvests: lavender
Lavender (Lavandula angustifolia) is a fragrant Mediterranean sub-shrub prized for its silver-gray foliage and intensely aromatic purple flower spikes. A classic companion for roses and an unmatched pollinator magnet, lavender thrives in the exact conditions that challenge many plants: poor, rocky, alkaline soil with excellent drainage and full sun. English lavender is the most cold-hardy species, reliably perennial in Zones 5–9. Fresh or dried flowers are widely used in sachets, essential oils, culinary applications, and dried arrangements.
Boulder, Utah is in USDA Zone 6a. The average last spring frost is May 27 and the first fall frost is September 21, giving you a growing season of approximately 117 days.
At an elevation of 5,058 feet, Garfield County receives approximately 20.3 inches of rainfall annually with predominantly loam soil. Summer highs average 84°F, so choose short-season varieties of Lavender to ensure they mature before fall.
Boulder Soil Profile
Soil Type
Loam
Soil pH
6.5-7.7
Drainage
Well Drained
Lavender 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 Boulder
How your county's soil matches Lavender's growing requirements.
Soil pH
Your soil pH (6.5–7.7) overlaps with Lavender's range (6.5–7.5), though not a perfect match.
Soil Texture
The loam soil in Garfield County is excellent for Lavender — good drainage, moisture retention, and nutrient holding capacity.
Organic Matter
Organic matter is moderate (2.2%). Annual compost additions will help Lavender.
How to Plant Lavender
Lavender Water Budget
Water stress score is 8/10 — consider drought-tolerant varieties and mulching
Monthly Watering Guide for Lavender
Lavender needs approximately 0.3 inches of water per week (1.3" per month). Here's how your county's rainfall compares month by month.
| Month | Lavender Needs | Rainfall | You Supplement | Action |
|---|---|---|---|---|
| Jan | — | 1.4" | 0" | ❄️ Dormant |
| Feb | — | 1.3" | 0" | ❄️ Dormant |
| Mar | — | 1.9" | 0" | ❄️ Dormant |
| Apr | — | 2.1" | 0" | ❄️ Dormant |
| May | 1.3" | 2.3" | 0" | ✅ Rainfall sufficient |
| Jun | 1.3" | 1.4" | 0" | ✅ Rainfall sufficient |
| Jul | 1.3" | 1.6" | 0" | ✅ Rainfall sufficient |
| Aug | 1.3" | 2" | 0" | ✅ Rainfall sufficient |
| Sep | 1.3" | 1.8" | 0" | ✅ Rainfall sufficient |
| Oct | — | 2" | 0" | ❄️ Dormant |
| Nov | — | 1.5" | 0" | ❄️ Dormant |
| Dec | — | 1" | 0" | ❄️ Dormant |
Water needs are for active growing months only (May–Sep in Garfield County). Supplement amounts are based on average rainfall — actual needs vary with temperature, soil, and mulching.
Lavender 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.
Lavender Planting Timeline — Boulder, UT
Lavender Planting Calendar
| Activity | When | Date Range |
|---|---|---|
| Start Indoors | March 18 | Mar 18 – Apr 1 |
| Transplant Outdoors | June 10 | Jun 10 – Jun 24 |
| Bloom | August 19 | Aug 19 – Oct 14 |
Plant 0.5" deep · 18" apart · Rows 24" apart
Month-by-Month Timeline
| Month | Activities |
|---|---|
| January | — |
| February | — |
| March | Start Indoors |
| April | Start Indoors |
| May | — |
| June | Transplant Outdoors |
| July | — |
| August | Bloom |
| September | Bloom |
| October | Bloom |
| November | — |
| December | — |
Growing Conditions
☀️ Sun
Full Sun (6-8+ hours)
💧 Water
0.3"/week · Natural rainfall sufficient
📅 Days to Maturity
90–120 days
🧪 Soil pH
Needs 6.5–7.5 · Your soil: acceptable
🗺️ USDA Zone
Zone 6a
📆 Growing Season
117 days in Garfield County
Growing Tips for Lavender in Boulder
Direct sow Lavender outdoors after May 27 in Garfield County when soil has warmed and frost danger has passed.
Your 117.0-day growing season in Garfield County is tight for Lavender (90.0-120.0 days to maturity). Start indoors and choose early-maturing varieties.
General growing tips
The single most important requirement for lavender success is excellent drainage — it will rot in heavy clay or wet winter soils before cold alone kills it. Amend with coarse sand or fine gravel if needed; raised beds work well in Zones 5–6. Start from rooted cuttings or transplants rather than seed for named cultivars. Transplant after last frost when soil is reliably warm (55°F+). Avoid rich or overly moist soils. Prune lightly after each flush of bloom, but never cut into old wood below the green growth zone — it will not regenerate from leafless woody stems. In Zones 5–6, mulch lightly with gravel (not bark/organic material which traps moisture) around the crown for winter protection. Year 2+ plants develop into full, mature shrubs with the most prolific bloom.
Companion Planting
Good Companions
Check more plant combinations with our Companion Planting Checker →
Lavender in Other Locations
Your Garfield County Garden Planner — Free
A 22-page printable planner built for Garfield 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.