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Boulder County, CO — Planting Guide

Boulder County, Colorado Zone 6a June

Boulder County, Colorado gardeners: here's your June plan

June rewards gardeners who work with the weather, not against it. Here's how to stay in step this month in Boulder County, Colorado.

Avg. last frost May 14
Avg. first frost September 26
Soil temp (4") 46°F
Watering High
Pest pressure High
Daylight 14.8 hrs
  1. Time to transplant alpine strawberries, aronia, and blackberries

    Your last frost (May 14) has passed. These warm-season crops can handle outdoor soil now.

  2. Start cucumber, kale, and lettuce under lights

    Your window is short. These crops want several weeks of indoor growth before they go outside.

  3. Basket week: lettuce, radish, and anemones

    Morning harvests are best — cooler temperatures mean crisper produce and longer fridge life.

July will be here before you know it — start on
  • Starting indoors: basil, peppers, and pole beans
  • First harvests: basil, carrots, and cucumber
  • Fall sowing: carrots, kale, and lettuce

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Boulder County is in USDA Zone 6a. The average last spring frost is May 14 and the first fall frost is September 26, giving you a growing season of approximately 135 days.

At an elevation of 7,657 ft, Boulder County receives approximately 22.2 in of rainfall annually. Summer highs average 86°F with winter lows around 14°F. The predominant soil type is Loam.

Based on 31 years of NOAA climate station data, the last frost date here varies by 46 days year to year — ranging from April 24 in warm years to June 10 in cold years. The growing season is trending longer by about 3.71 days per decade. Boulder County scores 34/100 (Challenging) on the Microclimate Index.

🌡️ Zone

6a (-10°F to -5°F min)

❄️ Last Frost

May 14

🍂 First Frost

September 26

📅 Growing Season

135 days

⛰️ Elevation

7,657 ft

🌧️ Annual Rainfall

22.2 in

Boulder County, CO Short season
135 days
❄
Last Spring Frost May 14
➔ 135 growing days ➔
❄
First Fall Frost September 26

Monthly Watering Calendar for Boulder County

When you'll need to water your garden — based on average monthly rainfall vs. the ~1 inch/week most gardens need.

What this means for you: In humid climates, watering is usually about timing (morning, not evening, to prevent disease) more than volume. In dry climates, it's about depth (water deep, less often) more than frequency. Boulder County's 22" annual tells you which side you're on.

1"/wk 0" 1.3" 2.5" 3.8" 5" Jan 1.7" Feb 1.3" Mar 1.8" +2.1" Apr 2.2" +1.3" May 3" +2.7" Jun 1.6" +2.3" Jul 2" +2.2" Aug 2.1" +2.2" Sep 2.1" +2.4" Oct 1.9" Nov 1.4" Dec 1.2"
Rainfall sufficient Supplemental water needed Heavy watering required - - - 1"/week garden need
View detailed monthly data
MonthAvg RainfallRainy DaysExtra Water NeededWatering Effort
Jan 1.7 in 7 days — None
Feb 1.3 in 5 days — None
Mar 1.8 in 6 days — None
Apr 2.2 in 9 days 2.1 in High
May 3 in 7 days 1.3 in Moderate
Jun 1.6 in 4 days 2.7 in High
Jul 2 in 6 days 2.3 in High
Aug 2.1 in 6 days 2.2 in High
Sep 2.1 in 5 days 2.2 in High
Oct 1.9 in 5 days 2.4 in High
Nov 1.4 in 5 days — None
Dec 1.2 in 7 days — None

Annual total: 22.3 in. Water needs vary by crop — tomatoes need ~1.2"/week while herbs like rosemary need only 0.3"/week. Check individual plant pages for crop-specific water budgets that factor in your county's rainfall and soil drainage.

Boulder County Soil Profile

Soil Type

Loam

Soil pH

6.7-8

Drainage

Well Drained

Frost Risk Probability

Based on 31 years of NOAA weather station data from 3 stations

Too early frost risk Safe to Plant May 14 → Sep 26 135 frost-free days Protect crops frost returns Apr May Jun Jul Aug Sep Oct Nov Safe: Jun 10 Protect by: Oct 16

Beginners: Plant frost-sensitive crops (tomatoes, peppers, squash) after the "Safe" date on the left. Harvest or cover them before the "Protect by" date on the right. Hardy crops (lettuce, peas, kale) can go in the yellow transition zones.

How to read this table: "Conservative" means you're safe from frost 9 out of 10 years — best for beginners and frost-sensitive crops. "Average year" is the typical date. "Aggressive" means only 1 in 10 years is that warm — experienced gardeners with frost protection can try these dates.

Planting Strategy Last Spring Frost First Fall Frost Frost-Free Days
Conservative (safest) Jun 10 Oct 16 128 days
Cautious May 25 Oct 7 135 days
Average year May 14 Sep 26 135 days
Optimistic May 3 Sep 20 140 days
Aggressive (risky) Apr 24 Sep 8 137 days
📊
How predictable are frost dates here?

Not very — frost dates can vary by ±46 days year-to-year. Use the "Conservative" row in the table below, and keep row covers handy for surprise late frosts.

🌱
Is the growing season changing?

Yes — growing seasons are getting longer here (about 3.7 days per decade). Spring is arriving earlier than it used to. Good news for gardeners.

Gardening Difficulty Score

34 Challenging
Frost Timing Risk
10.0/10
Drought Risk
5.5/10
Soil Difficulty
1.0/10
Altitude Challenge
10.0/10
Climate Shift
10.0/10
Rainfall Challenge
3.1/10

Boulder County has challenging growing conditions. Season extension and careful variety selection are essential.

Zone 6a Frost Countdown
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Last Frost: May 14 First Frost: Sep 26

Local Gardening Help in Boulder County

Free expert help is closer than you think. Your county's cooperative extension office connects you with trained gardeners, soil testing labs, and local programs — all specific to Boulder County's climate and soil.

County Extension Office

Boulder County Colorado State University Extension Extension Office

Phone: 970-491-6281

Visit Extension Office Website →

Extension offices are run by land-grant universities and funded by the USDA. Their advice is free, research-based, and tailored to your county's specific conditions.

Master Gardener Program

Free gardening help from trained volunteers

Master Gardeners are community volunteers who complete 40–60 hours of university horticultural training. They answer gardening questions, diagnose plant problems, and offer workshops — all free.

Find Master Gardeners in CO →

Many extension offices run a Master Gardener hotline where you can call or email with photos of plant problems for free diagnosis.

Soil Testing

Available through your extension office

Before amending your soil, get it tested. Your extension office offers soil testing (typically $10–$25) that tells you exact pH, nutrient levels, and amendment recommendations specific to what you want to grow.

Request a Soil Test →

Services Available in Boulder County

Soil testing High-altitude gardening Water conservation Pest diagnostics
Finding local nurseries & garden centers in Boulder County

Why Buy Local

Local nurseries carry plants that are proven to grow in your area. Staff can give you advice specific to Boulder County's soil and climate that big-box stores can't. Plants from local growers are typically hardier because they're already acclimated to your zone.

How to Find Them

Search for "nurseries near Boulder County CO" or "garden center Boulder County" on Google Maps. Also check with your extension office — they often maintain lists of reputable local nurseries and plant sales.

Community gardens & gardening groups

Community gardens are a great way to learn from experienced gardeners in your area, especially if you're limited on space. Search "community garden Boulder County CO" or check your extension office and local parks department. Facebook groups like "Boulder County Gardeners" or "Colorado Gardening" are also excellent for local advice and plant swaps.

What to Plant After Your Harvest

After your first crops finish, use the remaining frost-free days to grow a second round.

After Spinach (harvest ends Aug 20) 37 days until frost
Radish 22-35d Lettuce 30-60d Crocus 10-20d Hyacinths 14-28d Tulips 15-30d
After Chard (harvest ends Aug 27) 30 days until frost
Radish 22-35d Lettuce 30-60d Crocus 10-20d Hyacinths 14-28d Tulips 15-30d
After Sweet Corn (harvest ends Aug 27) 30 days until frost
Radish 22-35d Lettuce 30-60d Crocus 10-20d Hyacinths 14-28d Tulips 15-30d
After Carrots (harvest ends Aug 20) 37 days until frost
Radish 22-35d Lettuce 30-60d Crocus 10-20d Hyacinths 14-28d Tulips 15-30d
After Broccoli (harvest ends Aug 27) 30 days until frost
Radish 22-35d Lettuce 30-60d Crocus 10-20d Hyacinths 14-28d Tulips 15-30d
After Lettuce (harvest ends Aug 27) 30 days until frost
Radish 22-35d Crocus 10-20d Hyacinths 14-28d Tulips 15-30d Daffodils 20-40d
Show 6 more succession options
After Beets (harvest ends Aug 6) 51 days until frost
Radish 22-35d Lettuce 30-60d Zucchini 45-60d Basil 50-75d Cucumber 50-70d
After Mustard Greens (harvest ends Aug 20) 37 days until frost
Radish 22-35d Lettuce 30-60d Crocus 10-20d Hyacinths 14-28d Tulips 15-30d
After Chervil (harvest ends Aug 20) 37 days until frost
Radish 22-35d Lettuce 30-60d Crocus 10-20d Hyacinths 14-28d Tulips 15-30d
After Bleeding Hearts (harvest ends Aug 20) 37 days until frost
Radish 22-35d Lettuce 30-60d Crocus 10-20d Hyacinths 14-28d Tulips 15-30d
After Napa Cabbage (harvest ends Aug 13) 44 days until frost
Radish 22-35d Lettuce 30-60d Crocus 10-20d Hyacinths 14-28d Tulips 15-30d
After Chicory (harvest ends Aug 27) 30 days until frost
Radish 22-35d Lettuce 30-60d Crocus 10-20d Hyacinths 14-28d Tulips 15-30d

Sunlight & Day Length in Boulder County

Monthly daylight hours and peak sun — critical for onion varieties, photoperiod-sensitive plants, and solar garden planning.

Why it matters: The longest day at Boulder County's latitude gets longer the further north you go. Strawberries, garlic, onions all care. The shortest day gets shorter — which limits winter growing for greens without artificial light.

Longest Day

14.8 hours

Summer solstice daylight

Shortest Day

9.2 hours

Winter solstice daylight

Peak Sun Hours

10.1 hr/day peak (summer)

Peak sun hours (green dashed line below) account for cloud cover — this is the usable direct sunlight your garden actually receives. Most vegetables need 6+ peak sun hours.

14hr 12hr 3h 6h 10h 13h 16h Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Daylight hours (sunrise to sunset) Peak sun hours (direct sunlight after cloud cover) ▪ Gold zone = long day (14+ hr) ▪ Blue zone = short day (<12 hr)

Onion tip: Your long summer days (14+ hours) support long-day onion varieties like Walla Walla, Sweet Spanish, and Ailsa Craig.

View detailed monthly data
MonthDaylight HoursPeak Sun HoursDay Length
January 9.5 hr 5.4 hr Short day
February 10.5 hr 6.1 hr Short day
March 11.7 hr 6.9 hr Short day
April 13.1 hr 7.4 hr Neutral
May 14.2 hr 8.5 hr Long day
June 14.8 hr 10.1 hr Long day
July 14.6 hr 9.9 hr Long day
August 13.6 hr 9.7 hr Neutral
September 12.2 hr 8.9 hr Neutral
October 10.9 hr 6.9 hr Short day
November 9.7 hr 5.6 hr Short day
December 9.2 hr 4.9 hr Short day

Peak sun hours factor in typical cloud cover — use these for solar panel and shade-planning calculations.

Soil Temperature & Composting in Boulder County

Monthly soil temps tell you when to plant warm-season crops, and when your compost pile is actively working.

Why it matters: Soil temperature predicts plant emergence better than calendar dates. Boulder County's spring soil warm-up curve tells you which weeks are safe for direct-sow beans, cucumbers, squash, and corn.

Plant Warm Crops When

Soil reaches 60°F+

Soil rarely reaches 60°F — use black plastic mulch to warm soil.

Best Month to Compost

Jul

Microbial activity peaks when soil is warm.

Active Composting

2 months

Short season — insulate pile or use indoor vermicomposting.

60°F 0° 18° 35° 53° 70° Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
4" depth 8" depth - - - 60°F (corn, beans) - - - 70°F (tomatoes, peppers)
View detailed monthly data
MonthSoil 4" DeepSoil 8" DeepCompost ActivityTime to Finish
Jan 1°F 8°F ❄️ Dormant ~36 weeks
Feb 0°F 6°F ❄️ Dormant ~36 weeks
Mar 7°F 10°F ❄️ Dormant ~36 weeks
Apr 21°F 23°F ❄️ Dormant ~36 weeks
May 37°F 31°F ❄️ Dormant ~36 weeks
Jun 46°F 40°F 🐢 Slow ~24 weeks
Jul 54°F 49°F ♻️ Active ~14 weeks
Aug 53°F 49°F ♻️ Active ~14 weeks
Sep 49°F 46°F 🐢 Slow ~24 weeks
Oct 34°F 36°F ❄️ Dormant ~36 weeks
Nov 18°F 25°F ❄️ Dormant ~36 weeks
Dec 6°F 15°F ❄️ Dormant ~36 weeks

Highlighted rows = soil 60°F+ (safe for warm-season transplants). Compost finishes fastest during peak activity months.

Pest & Disease Pressure in Boulder County

Computed from local climate patterns — warmer, humid conditions increase pest generations and fungal disease risk.

Why this matters: Pest and disease pressure is the X-factor most beginners under-plan for. Boulder County's climate determines whether you can mostly "plant and see" or whether you need a pest-management routine from the first seedling.

Insect Pest Pressure

5.2 / 10

Moderate — common pests appear but manageable with monitoring.

Disease Risk

2 / 10

Low disease risk — dry conditions reduce fungal problems.

Seasonal Risk

Spring Low
Summer High
Fall Low
Winter Low
View 6 common pests in your area
PestRisk LevelPeak Months
Aphids Moderate May, Jun, Jul, Aug
Japanese beetles Moderate Jun, Jul, Aug
Squash bugs Low Jun, Jul, Aug
Tomato hornworms Low Jul, Aug
Cabbage loopers Low May, Jun, Jul, Aug
Slugs Low Apr, May, Jun
Organic pest management tips
  • Maintain healthy soil with regular compost additions to build natural pest resistance
  • Practice crop rotation annually to break pest cycles
  • Encourage beneficial insects with flowering herbs like dill, fennel, and yarrow

Cover Crops for Boulder County

Cover crops protect bare soil, fix nitrogen, suppress weeds, and improve soil structure — with planting dates calibrated for your area.

Why this matters: Bare soil is wasted soil — it loses nutrients to rain, dries out, compacts, and gets taken over by weeds. Cover crops (clovers, ryegrass, vetch, peas) are the "between seasons" trick that makes soil better every year. In Boulder County, you can fit a cover crop into the gaps.

Spring Cover Crops (3 options) — Build soil before the main growing season
Crop Plant By Terminate N-Fixing Soil Benefit
Buckwheat May 17 Aug 1 — Rapid growth, attracts pollinators, suppresses weeds
Sorghum-sudan grass May 25 Jul 25 — Massive biomass, breaks compaction, suppresses nematodes
White clover Apr 14 Aug 1 ✓ Yes Living mulch, fixes nitrogen, permanent ground cover
Summer Cover Crops (1 options) — Fill gaps and suppress weeds between plantings
Crop Plant By Terminate N-Fixing Soil Benefit
Sunflowers May 27 Sep 12 — Deep roots break compaction, attract pollinators and beneficial insects
Fall Cover Crops (6 options) — Plant after harvest to protect soil over winter
Crop Plant By Terminate N-Fixing Soil Benefit
Austrian winter peas Jul 23 Apr 30 ✓ Yes Fixes nitrogen, good for heavy clay soils
Daikon radish Aug 15 Apr 23 — Deep taproot breaks compaction, excellent for clay soils
Hairy vetch Jul 18 Apr 30 ✓ Yes Excellent nitrogen fixer, good for depleted soils
Oats Aug 27 Apr 23 — Quick biomass, winterkills in cold zones — no spring tillage needed
Winter rye Jun 30 Apr 23 — Suppresses weeds, prevents erosion, breaks up compacted soil
Winter wheat Jul 2 Apr 30 — Erosion control, weed suppression, good biomass

Wind & Microclimate in Boulder County

Quick context: Wind shapes the garden you don't think about: bee paths, evaporation, structural stress on tomato cages. Boulder County's 11.0 mph background level is a baseline you should know before placing the tallest crops (sunflowers, pole beans, sweet corn).

Wind dries soil, stresses plants, and affects frost patterns. Understanding your exposure helps with garden placement.

Seasonal Wind Speed

Spring: 16 mph   Summer: 11 mph

Fall: 12 mph   Winter: 14 mph

Prevailing wind: W. Windy area — plant a windbreak hedge on the W side of your garden.

Windbreak Benefit

6.6/10

Moderately beneficial — a simple fence or trellis can protect delicate crops from wind stress.

Frost Pocket Risk

Moderate

Some terrain variation (792 ft range). Garden on slopes or higher ground if possible to avoid late-season frost pockets.

Rainwater Harvesting in Boulder County

How much water you can collect, when to collect it, and what size system you need for your garden.

Why it matters: Even in arid regions, rainwater harvesting works — you just need bigger storage and patience. In wet regions like Boulder County (22" annually), you're mostly limited by how much water you can store between storms.

Annual Collection

11,114 gal

Per 1,000 sq ft of roof area (at 80% collection efficiency)

Recommended Setup

7 rain barrels (55 gal each)

For a typical 500 sq ft garden. Serious collectors: consider a 1,750 gal tank.

Legal Status

Limited

Your state has quantity limits on rainwater collection — check local regulations before installing large systems.

Best Collection Months

Apr, May, Aug, Sep

Highest rainfall months — your barrels will fill up quickly during these months.

Months to Draw From Storage

Feb, Nov, Dec

Dry months when you'll rely on stored water — size your storage for this gap.

Rainwater collection tips for your area
  • Your county receives approximately 22.3 inches of rain per year
  • A 1,000 sq ft roof can collect roughly 11,114 gallons annually
  • Check CO state regulations — rainwater harvesting has quantity limits
  • Stock up on stored water before your dry season (Feb, Nov, Dec)
  • Use a first-flush diverter to keep roof debris out of your collection

Soil & Growing Conditions in Boulder County

Soil Type

Loam

Soil pH 6.7–8 · Excessively Drained drainage

Good candidate for raised beds to maximise drainage and extend the season.

Watering Needs

Drought stress: 5.5/10

Moderate drought pressure. Drip irrigation and mulching are highly recommended to maintain soil moisture through summer.

Season Tips

135-day frost-free season

Start warm-season crops indoors and focus on short-season varieties. Cold frames extend your season by 3–4 weeks in fall.

Your Free Printable Garden Planner

Plan every bed, every planting, every harvest — in one place. This 22-page printable includes your zone's planting calendar, a month-by-month task list, a seed inventory tracker, a harvest log, and succession-planting charts. Built to print, write in, and actually use all season.

Instant PDF download. No spam, unsubscribe any time.

Recommended for Your Garden

🧪
Soil Test Kit $12-25

Test your soil pH, nitrogen, phosphorus, and potassium levels before planting.

Know your soil before you plant for best results.

📏
Digital pH Meter $10-20

Get instant, accurate soil pH readings to fine-tune your amendments.

Helpful for your garden setup.

🍂
Organic Compost $8-30

Boost soil fertility and structure with rich, well-aged organic compost.

Helpful for your garden setup.

🥬 Vegetables to Grow in Boulder County

107 vegetables that grow well in Zone 6a with planting dates for Boulder County.

Show all 107 vegetables with planting dates
Plant Start Indoors Direct Sow Transplant Fall Plant Harvest Days to Maturity
Acorn Squash Apr 9 May 21 May 28 — Aug 20 – Sep 24 80–100
Amaranth Mar 19 May 21 May 28 — Aug 27 – Oct 15 90–120
Arugula Apr 9 Apr 30 May 14 Jul 18 Jun 18 – Aug 20 30–50
Asparagus — — May 28 — — 730–1095
Beets — Apr 30 — Jul 18 Jun 25 – Jul 23 50–70
Belgian Endive Apr 9 Apr 30 May 14 Jul 18 Sep 3 – Oct 29 110–150
Bitter Melon Mar 19 May 21 May 28 — Jul 30 – Sep 10 60–90
Black Beans — May 21 — — Aug 20 – Oct 8 90–120
Bok Choy Apr 9 Apr 30 May 14 Jul 18 Jun 25 – Jul 30 40–60
Broccoli Apr 9 Apr 30 May 14 Jul 18 Jul 16 – Aug 27 60–90
Broccoli Rabe Apr 9 Apr 30 May 14 Jul 18 Jun 25 – Jul 30 40–60
Brussels Sprouts Apr 9 Apr 30 May 14 Jul 18 Aug 13 – Oct 8 90–130
Butternut Squash Apr 9 May 21 May 28 — Aug 27 – Oct 1 85–110
Cabbage Apr 9 Apr 30 May 14 Jul 18 Jul 16 – Sep 10 60–100
Calabash Mar 19 May 21 May 28 — Aug 20 – Oct 15 80–120
Carrots — Apr 30 — Jul 18 Jul 2 – Aug 6 60–80
Cauliflower Apr 9 Apr 30 May 14 Jul 18 Jul 9 – Sep 10 55–100
Celeriac Apr 9 Apr 30 May 14 Jul 18 Aug 27 – Oct 1 100–120
Celery Apr 9 Apr 30 May 14 Jul 18 Aug 6 – Oct 1 80–120
Celtuce Apr 9 Apr 30 May 14 Jul 18 Jul 16 – Aug 27 60–90
Chard Apr 9 Apr 30 May 14 Jul 18 Jul 9 – Aug 27 50–60
Chickpeas Apr 9 Apr 30 May 14 Jul 18 Aug 6 – Sep 17 80–110
Chicory Apr 9 Apr 30 May 14 Jul 18 Jul 16 – Aug 27 60–85
Chinese Cabbage Apr 9 Apr 30 May 14 Jul 18 Jul 9 – Aug 6 50–70
Christmas Lima Beans Mar 19 May 21 May 28 — Aug 20 – Sep 24 80–100
Collard Greens Apr 9 Apr 30 May 14 Jul 18 Jul 9 – Sep 10 55–75
Corn — May 21 — — Jul 23 – Sep 17 60–100
Cowpeas — May 21 — — Jul 23 – Sep 3 60–90
Cress Apr 9 Apr 30 May 14 Jul 18 May 28 – Jun 18 14–21
Crookneck Squash Apr 9 May 21 May 28 — Jul 16 – Aug 13 45–60
Crosne — Apr 30 — Jul 18 Oct 1 – Nov 12 150–200
Cucumber Apr 9 May 21 May 28 — Jul 23 – Sep 17 50–70
Daikon — Apr 30 — Jul 18 Jun 25 – Jul 23 50–70
Delicata Squash Apr 9 May 21 May 28 — Aug 20 – Sep 24 80–100
Edamame — May 21 — — Aug 6 – Sep 17 75–100
Eggplant Mar 5 May 21 May 28 — Aug 6 – Oct 8 65–85
Endive Apr 9 Apr 30 May 14 Jul 18 Jul 2 – Aug 6 45–65
Escarole Apr 9 Apr 30 May 14 Jul 18 Jul 9 – Aug 6 50–70
Fava Beans Apr 9 Apr 30 May 14 Jul 18 Jul 30 – Sep 10 75–100
Fennel Mar 19 May 21 May 28 — Jul 30 – Sep 10 60–90
Garlic — — — Aug 15 Nov 14 – Feb 27 90–240
Green Beans — May 21 — — Jul 16 – Sep 10 50–65
Horseradish — — May 28 — Oct 1 – Dec 10 120–180
Hot Peppers Mar 5 May 21 May 28 — Aug 6 – Nov 12 70–120
Hubbard Squash Apr 9 May 21 May 28 — Sep 10 – Oct 15 100–120
Kabocha Apr 9 May 21 May 28 — Aug 27 – Sep 24 85–100
Kai Lan Apr 9 Apr 30 May 14 Jul 18 Jul 2 – Jul 30 45–60
Kale Apr 9 Apr 30 May 14 Jul 18 Jul 9 – Sep 3 50–70
Kidney Beans — May 21 — — Aug 20 – Sep 24 85–110
Kohlrabi Apr 9 Apr 30 May 14 Jul 18 Jul 2 – Aug 6 45–65
Komatsuna Apr 9 Apr 30 May 14 Jul 18 Jun 18 – Jul 23 35–50
Leeks Apr 9 Apr 30 May 14 Jul 18 Aug 13 – Oct 29 90–150
Lentils Apr 9 Apr 30 May 14 Jul 18 Aug 6 – Sep 17 80–110
Lettuce Apr 9 Apr 30 May 14 Jul 18 Jun 18 – Aug 27 30–60
Lima Beans — May 21 — — Jul 23 – Sep 3 60–90
Loofah Mar 19 May 21 May 28 — Sep 10 – Nov 12 100–150
Luffa Mar 19 May 21 May 28 — Aug 27 – Nov 12 90–150
Mache Apr 9 Apr 30 May 14 Jul 18 Jun 25 – Jul 30 40–60
Melon Apr 9 May 21 May 28 — Aug 6 – Sep 24 70–100
Microgreens Apr 9 Apr 30 May 14 Jul 18 May 21 – Jun 18 7–21
Mitsuba Apr 9 Apr 30 May 7 Jul 18 Jul 2 – Aug 27 50–70
Mizuna Apr 9 Apr 30 May 14 Jul 18 Jun 18 – Jul 16 30–45
Mustard Greens Apr 9 Apr 30 May 14 Jul 18 Jun 18 – Aug 20 30–50
Napa Cabbage Apr 9 Apr 30 May 14 Jul 18 Jul 9 – Aug 13 55–75
New Zealand Spinach Mar 19 May 21 May 28 — Jul 23 – Aug 20 55–70
Okra Mar 19 May 21 May 28 — Jul 23 – Sep 17 50–65
Onion Apr 9 Apr 30 May 14 Jul 18 Aug 13 – Oct 1 90–120
Pac Choi Apr 9 Apr 30 May 14 Jul 18 Jun 25 – Jul 23 40–55
Parsnip — Apr 30 — Jul 18 Aug 13 – Sep 24 100–130
Patty Pan Squash Apr 9 May 21 May 28 — Jul 16 – Aug 13 45–60
Peas Apr 9 Apr 30 May 14 Jul 18 Jul 9 – Sep 3 55–70
Peppers Mar 5 May 21 May 28 — Jul 30 – Oct 8 60–90
Pole Beans Mar 19 May 21 May 28 — Jul 23 – Sep 17 55–70
Potatoes Mar 19 May 21 May 28 — Aug 6 – Oct 15 70–120
Pumpkin Apr 9 May 21 May 28 — Aug 27 – Oct 15 85–120
Purslane Apr 9 Apr 30 May 14 Jul 18 Jun 25 – Jul 30 40–60
Radicchio Apr 9 Apr 30 May 14 Jul 18 Jul 16 – Aug 20 60–80
Radish — Apr 30 — Jul 18 May 28 – Jun 18 22–35
Rhubarb — — Jun 4 — — 365–730
Romanesco Apr 9 Apr 30 May 14 Jul 18 Jul 30 – Sep 10 75–100
Rutabaga — Apr 30 — Jul 18 Jul 23 – Aug 27 80–100
Salsify — Apr 30 — Jul 18 Aug 13 – Sep 24 100–130
Savoy Cabbage Apr 9 Apr 30 May 14 Jul 18 Jul 23 – Sep 17 70–110
Scallions Apr 9 Apr 30 May 14 Jul 18 Jul 9 – Aug 6 50–70
Scarlet Runner Beans Mar 19 May 21 May 28 — Jul 30 – Sep 3 60–80
Shallot Apr 9 Apr 30 May 14 Jul 18 Aug 13 – Oct 1 90–120
Shiso Mar 26 May 21 May 28 — Jul 23 – Sep 17 50–70
Snap Peas Mar 19 May 21 May 28 — Jul 23 – Sep 17 55–70
Snow Peas Apr 9 Apr 30 May 14 Jul 18 Jul 9 – Sep 3 50–65
Soybeans — May 21 — — Aug 13 – Oct 8 80–120
Spaghetti Squash Apr 9 May 21 May 28 — Aug 27 – Sep 24 85–100
Spinach Apr 9 Apr 30 May 14 Jul 18 Jun 18 – Aug 20 35–50
Squash (Summer) Apr 9 May 21 May 28 — Jul 16 – Sep 17 45–65
Squash (Winter) Apr 9 May 21 May 28 — Aug 20 – Oct 15 80–120
Sunchoke — — May 28 — Sep 17 – Nov 12 110–150
Sweet Corn — May 21 — — Jul 23 – Sep 3 60–90
Sweet Potatoes Mar 19 May 21 May 28 — Aug 27 – Oct 15 90–120
Tatsoi Apr 9 Apr 30 May 14 Jul 18 Jun 18 – Jul 23 35–50
Tomatillo Mar 19 May 21 May 28 — Jul 30 – Oct 8 60–85
Tomatoes Mar 19 May 21 May 28 — Jul 30 – Oct 8 60–85
Turnip — Apr 30 — Jul 18 Jun 11 – Jul 16 40–60
Watercress Apr 9 Apr 30 May 14 Jul 18 Jun 25 – Jul 30 40–60
Watermelon Apr 9 May 21 May 28 — Aug 6 – Sep 24 70–100
Wax Beans — May 21 — — Jul 16 – Sep 10 50–65
Winter Melon Mar 19 May 21 May 28 — Aug 27 – Oct 15 90–120
Yard Long Beans Mar 19 May 21 May 28 — Jul 23 – Sep 3 55–80
Zucchini Apr 9 May 21 May 28 — Jul 16 – Sep 10 45–60

🍓 Fruits to Grow in Boulder County

27 fruits that grow well in Zone 6a with planting dates for Boulder County.

Show all 27 fruits with planting dates
Plant Start Indoors Direct Sow Transplant Fall Plant Harvest Days to Maturity
Alpine Strawberries — — Jun 4 — Sep 3 – Dec 17 90–180
Aronia — — Jun 4 — — 730–1095
Blackberries — — Jun 4 — — 365–730
Blueberries — — Jun 4 — — 730–1095
Boysenberries — — Jun 4 — — 365–730
Cantaloupe — — Jun 4 — Aug 13 – Sep 17 70–90
Che Fruit — — Jun 4 — — 1095–1825
Cranberries — — Jun 4 — — 730–1095
Currants — — Jun 4 — — 730–1095
Elderberries — — Jun 4 — — 730–1095
Goji Berries — — Jun 4 — — 730–1095
Gooseberries — — Jun 4 — — 730–1095
Grapes — — Jun 4 — — 730–1095
Ground Cherry — — Jun 4 — Aug 13 – Oct 8 65–80
Hardy Kiwi — — Jun 4 — — 1095–1825
Haskaps — — Jun 4 — — 730–1095
Honeydew — — Jun 4 — Aug 27 – Oct 8 80–110
Jostaberry — — Jun 4 — — 730–1095
Lingonberries — — Jun 4 — — 730–1095
Medlar — — Jun 4 — — 1095–1825
Mulberries — — Jun 4 — — 730–1825
Pawpaw — — Jun 4 — — 1095–2555
Persimmon — — Jun 4 — — 1095–2555
Quince — — Jun 4 — — 1095–1825
Raspberries — — Jun 4 — — 365–730
Serviceberries — — Jun 4 — — 730–1095
Strawberries — — Jun 4 — Sep 3 – Dec 17 90–365

🌿 Herbs to Grow in Boulder County

35 herbs that grow well in Zone 6a with planting dates for Boulder County.

Show all 35 herbs with planting dates
Plant Start Indoors Direct Sow Transplant Fall Plant Harvest Days to Maturity
Angelica Apr 9 Apr 30 May 7 Jul 18 — 365–730
Anise Apr 9 Apr 30 May 7 Jul 18 Aug 6 – Oct 22 90–120
Basil Mar 26 May 21 May 28 — Jul 23 – Sep 24 50–75
Bee Balm — — May 21 — Aug 20 – Nov 5 90–120
Borage Apr 9 Apr 30 May 7 Jul 18 Jul 2 – Aug 20 50–60
Caraway Apr 9 Apr 30 May 7 Jul 18 — 365–450
Catnip — — May 21 — Jul 23 – Sep 24 60–80
Chamomile Apr 9 Apr 30 May 7 Jul 18 Jul 9 – Sep 17 60–90
Chervil Apr 9 Apr 30 May 7 Jul 18 Jun 18 – Aug 20 40–60
Chives — — May 21 — Jul 23 – Oct 1 60–90
Cilantro Apr 9 Apr 30 May 7 Jul 18 Jun 18 – Aug 20 40–60
Comfrey — — May 21 — Jul 23 – Oct 1 60–90
Cumin Apr 9 Apr 30 May 7 Jul 18 Aug 20 – Oct 22 100–120
Dill Apr 9 Apr 30 May 7 Jul 18 Jun 18 – Aug 20 40–60
Epazote Mar 26 May 21 May 28 — Jul 16 – Sep 10 45–60
Fennel (herb) Apr 9 Apr 30 May 7 Jul 18 Jul 9 – Sep 17 60–90
Feverfew — — May 21 — Aug 20 – Nov 5 90–120
Garlic Chives — — May 21 — Jul 23 – Oct 1 60–90
Horehound — — May 21 — Aug 6 – Oct 1 75–90
Hyssop — — May 21 — Jul 30 – Oct 1 70–90
Lemon Balm — — May 21 — Jul 23 – Sep 10 60–70
Lemon Thyme — — May 21 — Jul 30 – Oct 1 70–90
Lovage — — May 21 — Jul 30 – Oct 1 70–90
Marjoram — — May 21 — Jul 23 – Oct 1 60–90
Mint — — May 21 — Jul 23 – Oct 1 60–90
Oregano — — May 21 — Jul 23 – Oct 1 60–90
Parsley Apr 9 Apr 30 May 7 Jul 18 Jul 9 – Sep 10 60–80
Rue — — May 21 — Jul 30 – Oct 1 70–90
Sage — — May 21 — Aug 6 – Oct 1 75–90
Savory — — May 21 — Jul 16 – Sep 10 50–70
Sorrel Apr 9 Apr 30 May 7 Jul 18 Jun 18 – Aug 20 40–60
Tarragon — — May 21 — Jul 23 – Oct 1 60–90
Thai Basil Mar 26 May 21 May 28 — Jul 23 – Sep 24 50–75
Thyme — — May 21 — Jul 30 – Oct 1 70–90
Valerian — — May 21 — Sep 24 – Dec 3 120–180

🌸 Flowers to Grow in Boulder County

53 flowers that grow well in Zone 6a with planting dates for Boulder County.

Show all 53 flowers with planting dates
Plant Start Indoors Direct Sow Transplant Fall Plant Bloom Days to Maturity
Ageratum Mar 26 May 14 May 14 — Jul 9 – Oct 15 60–75
Alliums — — — Aug 15 Sep 12 – Oct 10 28–42
Anemones Apr 16 — May 14 — Jun 18 – Jul 16 90–120
Astilbe Mar 12 — May 21 — Jul 30 – Oct 8 70–100
Bachelor's Button Apr 2 Apr 16 May 14 Aug 15 Jul 16 – Oct 1 60–90
Begonias Mar 5 — May 21 — Jul 30 – Oct 29 70–90
Black-eyed Susan Mar 12 May 14 May 21 — Aug 6 – Nov 19 60–80
Bleeding Hearts Mar 12 — May 21 — Jul 16 – Aug 20 60–90
Calendula Apr 2 Apr 16 May 14 — Jul 2 – Oct 1 50–70
California Poppy — Apr 16 — — Jun 25 – Aug 6 60–90
Celosia Apr 9 May 21 May 21 — Jul 23 – Nov 5 60–90
Columbine Mar 12 May 28 May 28 — Jul 23 – Aug 27 70–100
Coreopsis Mar 12 May 21 May 21 — Jul 30 – Nov 19 60–80
Cosmos Apr 16 May 14 May 14 — Jul 23 – Oct 29 60–90
Crocus — — — Aug 15 Jul 4 – Jul 25 10–20
Daffodils — — — Aug 15 Jul 11 – Aug 1 20–40
Dahlias Apr 16 May 21 May 21 — Aug 6 – Nov 19 70–120
Daylily Mar 12 — May 21 — Aug 6 – Nov 19 60–90
Dianthus Mar 19 Apr 16 Apr 30 — Jun 18 – Sep 17 60–80
Echinacea (Purple Coneflower) Mar 12 May 28 May 28 — Aug 20 – Nov 26 70–90
Foxglove Mar 12 May 21 May 21 — Jul 16 – Aug 20 80–120
Gaillardia (Blanket Flower) Mar 26 May 21 May 21 — Jul 30 – Dec 3 70–100
Geraniums Mar 5 — May 21 — Jul 30 – Oct 29 70–100
Gladiolus — May 14 May 14 — Jul 30 – Nov 12 70–100
Hostas Mar 5 — May 21 — Aug 6 – Nov 19 60–90
Hyacinths — — — Aug 15 Aug 1 – Aug 22 14–28
Hydrangeas Mar 5 — May 21 — Jul 30 – Nov 5 90–150
Impatiens Mar 19 — May 21 — Jul 30 – Nov 5 60–75
Irises — Division May 21 — Jul 16 – Aug 13 60–100
Larkspur — Apr 16 — — Jun 25 – Aug 20 60–90
Lavender Mar 5 — May 28 — Aug 6 – Oct 1 90–120
Lilies — Division May 21 — Jul 30 – Nov 5 70–120
Lobelia Mar 12 — Apr 30 — Jun 25 – Sep 17 70–80
Lupine Mar 12 May 21 May 21 — Jul 16 – Aug 20 75–100
Marigolds Apr 2 May 21 May 21 — Jul 16 – Oct 15 50–70
Nasturtium Apr 16 May 21 May 21 — Jul 16 – Nov 5 55–65
Pansy Mar 5 — May 14 Aug 1 Jul 9 – Sep 10 70–90
Peonies — Division May 21 — Jul 23 – Aug 27 90–120
Petunia Mar 19 — May 21 — Jul 30 – Nov 5 70–90
Phlox Mar 12 May 21 May 21 — Jul 30 – Oct 22 80–110
Portulaca Apr 9 May 21 May 21 — Jul 9 – Oct 22 50–70
Ranunculus Apr 2 — May 14 — Jun 25 – Jul 23 90–120
Roses Mar 5 — May 21 — Jul 30 – Nov 19 90–180
Salvia Mar 12 — May 21 — Jul 30 – Nov 5 70–90
Sedum (Stonecrop) Mar 12 — May 21 — Sep 10 – Nov 26 60–90
Snapdragon Mar 5 Apr 23 May 14 — Jul 23 – Oct 1 70–100
Sunflower Apr 23 May 21 May 21 — Aug 13 – Nov 5 70–100
Sweet Alyssum Mar 26 Apr 23 May 14 — Jun 25 – Sep 3 45–60
Sweet Pea Apr 2 Apr 9 May 14 — Jul 30 – Oct 8 65–85
Tulips — — — Aug 15 Jul 25 – Aug 22 15–30
Vinca (Annual) Mar 5 — May 21 — Jul 30 – Nov 5 70–90
Yarrow Mar 12 May 14 May 21 — Jul 30 – Nov 19 60–90
Zinnia Apr 16 May 21 May 21 — Jul 30 – Nov 5 60–70

Monthly Planting Guide for Boulder County