O'Brien County, IA — Planting Guide
O'Brien County is in USDA Zone 4b. The average last spring frost is May 1 and the first fall frost is October 5, giving you a growing season of approximately 157 days.
At an elevation of 658 ft, O'Brien County receives approximately 40.5 in of rainfall annually. Summer highs average 83°F with winter lows around 4°F. The predominant soil type is Silt Loam.
Based on 31 years of NOAA climate station data, the last frost date here varies by 27 days year to year — ranging from April 17 in warm years to May 15 in cold years. O'Brien County scores 75/100 (Good) on the Microclimate Index.
🌡️ Zone
4b (-25°F to -20°F min)
❄️ Last Frost
May 1
🍂 First Frost
October 5
📅 Growing Season
157 days
⛰️ Elevation
658 ft
🌧️ Annual Rainfall
40.5 in
Monthly Watering Calendar
When you'll need to water your garden — based on average monthly rainfall vs. the ~1 inch/week most gardens need.
View detailed monthly data
| Month | Avg Rainfall | Rainy Days | Extra Water Needed | Watering Effort |
|---|---|---|---|---|
| Jan | 1.6 in | 8 days | — | None |
| Feb | 1.7 in | 6 days | — | None |
| Mar | 2.5 in | 8 days | — | None |
| Apr | 3.8 in | 11 days | 0.5 in | Low |
| May | 5.1 in | 11 days | — | Low |
| Jun | 4.8 in | 9 days | — | Low |
| Jul | 4.5 in | 7 days | — | Low |
| Aug | 4.8 in | 9 days | — | Low |
| Sep | 3.2 in | 7 days | 1.1 in | Moderate |
| Oct | 3.6 in | 7 days | 0.7 in | Moderate |
| Nov | 2.6 in | 8 days | — | None |
| Dec | 2.4 in | 7 days | — | None |
Annual total: 40.6 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.
O'Brien County Soil Profile
Soil Type
Silt Loam
Soil pH
5.8-7.2
Drainage
Well Drained
Frost Risk Probability
Based on 31 years of NOAA weather station data from 3 stations
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) | May 15 | Oct 18 | 156 days |
| Cautious | May 7 | Oct 10 | 156 days |
| Average year | May 1 | Oct 5 | 157 days |
| Optimistic | Apr 23 | Oct 2 | 162 days |
| Aggressive (risky) | Apr 17 | Sep 20 | 156 days |
Not very — frost dates can vary by ±27 days year-to-year. Use the "Conservative" row in the table below, and keep row covers handy for surprise late frosts.
Slightly — seasons are trending a bit shorter (0.4 days/decade). Stay conservative with planting dates.
Gardening Difficulty Score
O'Brien County offers good growing conditions. A little planning around frost dates goes a long way.
Local Gardening Help in O'Brien 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 O'Brien County's climate and soil.
County Extension Office
O'Brien County Iowa State University Extension Extension Office
Phone: 515-294-6675
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.
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.
Services Available in O'Brien County
Finding local nurseries & garden centers in O'Brien County
Why Buy Local
Local nurseries carry plants that are proven to grow in your area. Staff can give you advice specific to O'Brien 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 O'Brien County IA" or "garden center O'Brien 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 O'Brien County IA" or check your extension office and local parks department. Facebook groups like "O'Brien County Gardeners" or "Iowa 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.
Show 6 more succession options
Sunlight & Day Length
Monthly daylight hours and peak sun — critical for onion varieties, photoperiod-sensitive plants, and solar garden planning.
Longest Day
15.2 hours
Summer solstice daylight
Shortest Day
8.8 hours
Winter solstice daylight
Peak Sun Hours
9.4 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.
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
| Month | Daylight Hours | Peak Sun Hours | Day Length |
|---|---|---|---|
| January | 9.2 hr | 3.6 hr | Short day |
| February | 10.3 hr | 4.7 hr | Short day |
| March | 11.6 hr | 5.4 hr | Short day |
| April | 13.2 hr | 6.7 hr | Neutral |
| May | 14.5 hr | 8 hr | Long day |
| June | 15.2 hr | 9.1 hr | Long day |
| July | 14.9 hr | 9.4 hr | Long day |
| August | 13.8 hr | 8.9 hr | Neutral |
| September | 12.3 hr | 7.2 hr | Neutral |
| October | 10.8 hr | 5.7 hr | Short day |
| November | 9.5 hr | 3.7 hr | Short day |
| December | 8.8 hr | 3.2 hr | Short day |
Peak sun hours factor in typical cloud cover — use these for solar panel and shade-planning calculations.
Soil Temperature & Composting Calendar
Monthly soil temps tell you when to plant warm-season crops, and when your compost pile is actively working.
Plant Warm Crops When
Soil reaches 60°F+
Soil warm enough from Jun through Sep.
Best Month to Compost
Jul
Microbial activity peaks when soil is warm.
Active Composting
6 months
Solid season. Piles go dormant in winter.
View detailed monthly data
| Month | Soil 4" Deep | Soil 8" Deep | Compost Activity | Time to Finish |
|---|---|---|---|---|
| Jan | 13°F | 25°F | ❄️ Dormant | ~36 weeks |
| Feb | 15°F | 22°F | ❄️ Dormant | ~36 weeks |
| Mar | 24°F | 28°F | ❄️ Dormant | ~36 weeks |
| Apr | 40°F | 41°F | 🐢 Slow | ~24 weeks |
| May | 55°F | 51°F | ♻️ Active | ~14 weeks |
| Jun | 64°F | 59°F | ♻️ Active | ~14 weeks |
| Jul | 72°F | 65°F | 🔥 Peak | ~8 weeks |
| Aug | 75°F | 70°F | 🔥 Peak | ~8 weeks |
| Sep | 64°F | 64°F | ♻️ Active | ~14 weeks |
| Oct | 54°F | 55°F | ♻️ Active | ~14 weeks |
| Nov | 36°F | 45°F | ❄️ Dormant | ~36 weeks |
| Dec | 23°F | 31°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 O'Brien County
Computed from local climate patterns — warmer, humid conditions increase pest generations and fungal disease risk.
Insect Pest Pressure
Moderate — common pests appear but manageable with monitoring.
Disease Risk
Moderate — watch for mildew and blight during wet periods.
Seasonal Risk
View 5 common pests in your area
| Pest | Risk Level | Peak Months |
|---|---|---|
| Aphids | Moderate | May, Jun, Jul, Aug |
| Cabbage worms | Low | Jun, Jul, Aug |
| Colorado potato beetle | Low | Jun, Jul |
| Flea beetles | Low | May, Jun, Jul |
| Slugs | Low | May, Jun, Jul, Aug, Sep |
Organic pest management tips
- Use row covers on susceptible crops during peak pest months
- Apply neem oil preventatively every 7-14 days during active pest season
- Interplant with strong-scented herbs (basil, marigold) to confuse pests
- Hand-pick larger pests (beetles, caterpillars) in early morning when they're sluggish
- Practice crop rotation — never plant the same family in the same spot within 3 years
Cover Crops for O'Brien County
Cover crops protect bare soil, fix nitrogen, suppress weeds, and improve soil structure — with county-specific planting dates.
Spring Cover Crops (2 options) — Build soil before the main growing season
| Crop | Plant By | Terminate | N-Fixing | Soil Benefit |
|---|---|---|---|---|
| Buckwheat | May 10 | Aug 3 | — | Rapid growth, attracts pollinators, suppresses weeds |
| White clover | Apr 4 | Aug 10 | ✓ 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 26 | Sep 21 | — | Deep roots break compaction, attract pollinators and beneficial insects |
Fall Cover Crops (5 options) — Plant after harvest to protect soil over winter
| Crop | Plant By | Terminate | N-Fixing | Soil Benefit |
|---|---|---|---|---|
| Daikon radish | Aug 23 | Apr 10 | — | Deep taproot breaks compaction, excellent for clay soils |
| Hairy vetch | Jul 26 | Apr 17 | ✓ Yes | Excellent nitrogen fixer, good for depleted soils |
| Oats | Sep 9 | Apr 17 | — | Quick biomass, winterkills in cold zones — no spring tillage needed |
| Winter rye | Jun 27 | Apr 17 | — | Suppresses weeds, prevents erosion, breaks up compacted soil |
| Winter wheat | Jul 10 | Apr 17 | — | Erosion control, weed suppression, good biomass |
Wind & Microclimate
Wind dries soil, stresses plants, and affects frost patterns. Understanding your exposure helps with garden placement.
Seasonal Wind Speed
Spring: 11 mph Summer: 10 mph
Fall: 9 mph Winter: 11 mph
Prevailing wind: SW. Moderate wind — consider a temporary windbreak for young seedlings.
Windbreak Benefit
4.5/10
Moderately beneficial — a simple fence or trellis can protect delicate crops from wind stress.
Frost Pocket Risk
Low
Relatively flat terrain (114 ft range). Frost pocket risk is minimal — garden placement is flexible.
Rainwater Harvesting Potential
How much water you can collect, when to collect it, and what size system you need for your garden.
Annual Collection
20,235 gal
Per 1,000 sq ft of roof area (at 80% collection efficiency)
Recommended Setup
6 rain barrels (55 gal each)
For a typical 500 sq ft garden. Serious collectors: consider a 1,500 gal tank.
Legal Status
Unrestricted
Rainwater harvesting is fully legal in your state with no restrictions.
Best Collection Months
May, Jun, Jul, Aug
Highest rainfall months — your barrels will fill up quickly during these months.
Months to Draw From Storage
Jan, Feb, 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 40.6 inches of rain per year
- A 1,000 sq ft roof can collect roughly 20,235 gallons annually
- Rainwater harvesting is fully legal in your state
- Stock up on stored water before your dry season (Jan, Feb, Dec)
- Use a first-flush diverter to keep roof debris out of your collection
Soil & Growing Conditions in O'Brien County
Soil Type
Silt Loam
Soil pH 5.8–7.2 · Well Drained drainage
Native soil is well-suited to most vegetables and herbs with regular compost additions.
Watering Needs
Drought stress: 3.5/10
Low-to-moderate drought stress. Plan to water 1–2 times per week during peak summer. (40.5 in. annual rainfall)
Season Tips
157-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.
Free Garden Planner
Plan your entire garden season — organize planting dates, track what you're growing, and know exactly when to start seeds, transplant, and harvest.
Recommended for Your Garden
Test your soil pH, nitrogen, phosphorus, and potassium levels before planting.
Get instant, accurate soil pH readings to fine-tune your amendments.
Boost soil fertility and structure with rich, well-aged organic compost.
🥬 Vegetables to Grow in O'Brien County
96 vegetables that grow well in Zone 4b with planting dates for O'Brien County.
Show all 96 vegetables with planting dates
| Plant | Start Indoors | Direct Sow | Transplant | Harvest | Days to Maturity |
|---|---|---|---|---|---|
| Acorn Squash | Mar 20 | May 15 | May 22 | Aug 14 – Sep 18 | 80–100 |
| Amaranth | Feb 27 | May 15 | May 22 | Aug 21 – Oct 9 | 90–120 |
| Arugula | Mar 20 | Apr 24 | May 1 | Jun 5 – Aug 7 | 30–50 |
| Asparagus | — | — | May 15 | — | 730–1095 |
| Beets | — | Apr 24 | — | Jun 19 – Jul 17 | 50–70 |
| Belgian Endive | Mar 20 | Apr 24 | May 1 | Aug 21 – Sep 25 | 110–150 |
| Black Beans | — | May 15 | — | Aug 14 – Oct 2 | 90–120 |
| Bok Choy | Mar 20 | Apr 24 | May 1 | Jun 12 – Jul 17 | 40–60 |
| Broccoli | Mar 20 | Apr 24 | May 1 | Jul 3 – Aug 14 | 60–90 |
| Broccoli Rabe | Mar 20 | Apr 24 | May 1 | Jun 12 – Jul 17 | 40–60 |
| Brussels Sprouts | Mar 20 | Apr 24 | May 1 | Jul 31 – Sep 25 | 90–130 |
| Butternut Squash | Mar 20 | May 15 | May 22 | Aug 21 – Sep 25 | 85–110 |
| Cabbage | Mar 20 | Apr 24 | May 1 | Jul 3 – Aug 28 | 60–100 |
| Carrots | — | Apr 24 | — | Jun 26 – Jul 31 | 60–80 |
| Cauliflower | Mar 20 | Apr 24 | May 1 | Jun 26 – Aug 28 | 55–100 |
| Celeriac | Mar 20 | Apr 24 | May 1 | Aug 14 – Sep 18 | 100–120 |
| Celery | Mar 20 | Apr 24 | May 1 | Jul 24 – Sep 18 | 80–120 |
| Celtuce | Mar 20 | Apr 24 | May 1 | Jul 3 – Aug 14 | 60–90 |
| Chard | Mar 20 | Apr 24 | May 1 | Jun 26 – Aug 14 | 50–60 |
| Chickpeas | Mar 20 | Apr 24 | May 1 | Jul 24 – Sep 4 | 80–110 |
| Chicory | Mar 20 | Apr 24 | May 1 | Jul 3 – Aug 14 | 60–85 |
| Chinese Cabbage | Mar 20 | Apr 24 | May 1 | Jun 26 – Jul 24 | 50–70 |
| Christmas Lima Beans | Feb 27 | May 15 | May 22 | Aug 14 – Sep 18 | 80–100 |
| Collard Greens | Mar 20 | Apr 24 | May 1 | Jun 26 – Aug 28 | 55–75 |
| Corn | — | May 15 | — | Jul 17 – Sep 11 | 60–100 |
| Cress | Mar 20 | Apr 24 | May 1 | May 15 – Jun 5 | 14–21 |
| Crookneck Squash | Mar 20 | May 15 | May 22 | Jul 10 – Aug 7 | 45–60 |
| Crosne | — | Apr 24 | — | Sep 25 – Sep 18 | 150–200 |
| Cucumber | Mar 20 | May 15 | May 22 | Jul 17 – Sep 11 | 50–70 |
| Daikon | — | Apr 24 | — | Jun 19 – Jul 17 | 50–70 |
| Delicata Squash | Mar 20 | May 15 | May 22 | Aug 14 – Sep 18 | 80–100 |
| Edamame | — | May 15 | — | Jul 31 – Sep 11 | 75–100 |
| Endive | Mar 20 | Apr 24 | May 1 | Jun 19 – Jul 24 | 45–65 |
| Escarole | Mar 20 | Apr 24 | May 1 | Jun 26 – Jul 24 | 50–70 |
| Fava Beans | Mar 20 | Apr 24 | May 1 | Jul 17 – Aug 28 | 75–100 |
| Fennel | Feb 27 | May 15 | May 22 | Jul 24 – Sep 4 | 60–90 |
| Garlic | — | — | — | — | 90–240 |
| Green Beans | — | May 15 | — | Jul 10 – Sep 4 | 50–65 |
| Horseradish | — | — | May 15 | Sep 18 – Oct 9 | 120–180 |
| Hubbard Squash | Mar 20 | May 15 | May 22 | Sep 4 – Oct 9 | 100–120 |
| Kabocha | Mar 20 | May 15 | May 22 | Aug 21 – Sep 18 | 85–100 |
| Kai Lan | Mar 20 | Apr 24 | May 1 | Jun 19 – Jul 17 | 45–60 |
| Kale | Mar 20 | Apr 24 | May 1 | Jun 26 – Aug 21 | 50–70 |
| Kidney Beans | — | May 15 | — | Aug 14 – Sep 18 | 85–110 |
| Kohlrabi | Mar 20 | Apr 24 | May 1 | Jun 19 – Jul 24 | 45–65 |
| Komatsuna | Mar 20 | Apr 24 | May 1 | Jun 5 – Jul 10 | 35–50 |
| Leeks | Mar 20 | Apr 24 | May 1 | Jul 31 – Sep 25 | 90–150 |
| Lentils | Mar 20 | Apr 24 | May 1 | Jul 24 – Sep 4 | 80–110 |
| Lettuce | Mar 20 | Apr 24 | May 1 | Jun 5 – Aug 14 | 30–60 |
| Lima Beans | — | May 15 | — | Jul 17 – Aug 28 | 60–90 |
| Mache | Mar 20 | Apr 24 | May 1 | Jun 12 – Jul 17 | 40–60 |
| Melon | Mar 20 | May 15 | May 22 | Jul 31 – Sep 18 | 70–100 |
| Microgreens | Mar 20 | Apr 24 | May 1 | May 8 – Jun 5 | 7–21 |
| Mitsuba | Mar 20 | Apr 24 | Apr 24 | Jun 19 – Aug 14 | 50–70 |
| Mizuna | Mar 20 | Apr 24 | May 1 | Jun 5 – Jul 3 | 30–45 |
| Mustard Greens | Mar 20 | Apr 24 | May 1 | Jun 5 – Aug 7 | 30–50 |
| Napa Cabbage | Mar 20 | Apr 24 | May 1 | Jun 26 – Jul 31 | 55–75 |
| Onion | Mar 20 | Apr 24 | May 1 | Jul 31 – Sep 18 | 90–120 |
| Pac Choi | Mar 20 | Apr 24 | May 1 | Jun 12 – Jul 10 | 40–55 |
| Parsnip | — | Apr 24 | — | Aug 7 – Sep 18 | 100–130 |
| Patty Pan Squash | Mar 20 | May 15 | May 22 | Jul 10 – Aug 7 | 45–60 |
| Peas | Mar 20 | Apr 24 | May 1 | Jun 26 – Aug 21 | 55–70 |
| Peppers | Feb 13 | May 15 | May 22 | Jul 24 – Oct 2 | 60–90 |
| Pole Beans | Feb 27 | May 15 | May 22 | Jul 17 – Sep 11 | 55–70 |
| Potatoes | Feb 27 | May 15 | May 22 | Jul 31 – Oct 9 | 70–120 |
| Pumpkin | Mar 20 | May 15 | May 22 | Aug 21 – Oct 9 | 85–120 |
| Purslane | Mar 20 | Apr 24 | May 1 | Jun 12 – Jul 17 | 40–60 |
| Radicchio | Mar 20 | Apr 24 | May 1 | Jul 3 – Aug 7 | 60–80 |
| Radish | — | Apr 24 | — | May 22 – Jun 12 | 22–35 |
| Rhubarb | — | — | May 29 | — | 365–730 |
| Romanesco | Mar 20 | Apr 24 | May 1 | Jul 17 – Aug 28 | 75–100 |
| Rutabaga | — | Apr 24 | — | Jul 17 – Aug 21 | 80–100 |
| Salsify | — | Apr 24 | — | Aug 7 – Sep 18 | 100–130 |
| Savoy Cabbage | Mar 20 | Apr 24 | May 1 | Jul 10 – Sep 4 | 70–110 |
| Scallions | Mar 20 | Apr 24 | May 1 | Jun 26 – Jul 24 | 50–70 |
| Scarlet Runner Beans | Feb 27 | May 15 | May 22 | Jul 24 – Aug 28 | 60–80 |
| Shallot | Mar 20 | Apr 24 | May 1 | Jul 31 – Sep 18 | 90–120 |
| Shiso | Mar 6 | May 8 | May 22 | Jul 17 – Sep 11 | 50–70 |
| Snap Peas | Feb 27 | May 15 | May 22 | Jul 17 – Sep 11 | 55–70 |
| Snow Peas | Mar 20 | Apr 24 | May 1 | Jun 26 – Aug 21 | 50–65 |
| Soybeans | — | May 15 | — | Aug 7 – Oct 2 | 80–120 |
| Spaghetti Squash | Mar 20 | May 15 | May 22 | Aug 21 – Sep 18 | 85–100 |
| Spinach | Mar 20 | Apr 24 | May 1 | Jun 5 – Aug 7 | 35–50 |
| Squash (Summer) | Mar 20 | May 15 | May 22 | Jul 10 – Sep 11 | 45–65 |
| Squash (Winter) | Mar 20 | May 15 | May 22 | Aug 14 – Oct 9 | 80–120 |
| Sunchoke | — | — | May 15 | Sep 4 – Oct 9 | 110–150 |
| Sunflower | Feb 27 | May 15 | May 22 | Jul 31 – Sep 18 | 70–100 |
| Sweet Corn | — | May 15 | — | Jul 17 – Aug 28 | 60–90 |
| Tatsoi | Mar 20 | Apr 24 | May 1 | Jun 5 – Jul 10 | 35–50 |
| Tomatillo | Feb 27 | May 15 | May 22 | Jul 24 – Oct 2 | 60–85 |
| Tomatoes | Feb 27 | May 15 | May 22 | Jul 24 – Oct 2 | 60–85 |
| Turnip | — | Apr 24 | — | Jun 5 – Jul 10 | 40–60 |
| Watercress | Mar 20 | Apr 24 | May 1 | Jun 12 – Jul 17 | 40–60 |
| Watermelon | Mar 20 | May 15 | May 22 | Jul 31 – Sep 18 | 70–100 |
| Wax Beans | — | May 15 | — | Jul 10 – Sep 4 | 50–65 |
| Zucchini | Mar 20 | May 15 | May 22 | Jul 10 – Sep 4 | 45–60 |
🍓 Fruits to Grow in O'Brien County
22 fruits that grow well in Zone 4b with planting dates for O'Brien County.
Show all 22 fruits with planting dates
| Plant | Start Indoors | Direct Sow | Transplant | Harvest | Days to Maturity |
|---|---|---|---|---|---|
| Alpine Strawberries | — | — | May 29 | Aug 28 – Oct 23 | 90–180 |
| Aronia | — | — | May 29 | — | 730–1095 |
| Blueberries | — | — | May 29 | — | 730–1095 |
| Cantaloupe | — | — | May 29 | Aug 7 – Sep 11 | 70–90 |
| Cranberries | — | — | May 29 | — | 730–1095 |
| Currants | — | — | May 29 | — | 730–1095 |
| Elderberries | — | — | May 29 | — | 730–1095 |
| Goji Berries | — | — | May 29 | — | 730–1095 |
| Gooseberries | — | — | May 29 | — | 730–1095 |
| Grapes | — | — | May 29 | — | 730–1095 |
| Ground Cherry | — | — | May 29 | Aug 7 – Oct 2 | 65–80 |
| Hardy Kiwi | — | — | May 29 | — | 1095–1825 |
| Haskaps | — | — | May 29 | — | 730–1095 |
| Honeydew | — | — | May 29 | Aug 21 – Oct 2 | 80–110 |
| Jostaberry | — | — | May 29 | — | 730–1095 |
| Lingonberries | — | — | May 29 | — | 730–1095 |
| Medlar | — | — | May 29 | — | 1095–1825 |
| Mulberries | — | — | May 29 | — | 730–1825 |
| Persimmon | — | — | May 29 | — | 1095–2555 |
| Raspberries | — | — | May 29 | — | 365–730 |
| Serviceberries | — | — | May 29 | — | 730–1095 |
| Strawberries | — | — | May 29 | Aug 28 – Oct 23 | 90–365 |
🌿 Herbs to Grow in O'Brien County
32 herbs that grow well in Zone 4b with planting dates for O'Brien County.
Show all 32 herbs with planting dates
| Plant | Start Indoors | Direct Sow | Transplant | Harvest | Days to Maturity |
|---|---|---|---|---|---|
| Angelica | Mar 20 | Apr 24 | Apr 24 | — | 365–730 |
| Anise | Mar 20 | Apr 24 | Apr 24 | Jul 24 – Sep 18 | 90–120 |
| Basil | Mar 6 | May 8 | May 22 | Jul 17 – Sep 18 | 50–75 |
| Bee Balm | — | — | May 8 | Aug 7 – Oct 2 | 90–120 |
| Borage | Mar 20 | Apr 24 | Apr 24 | Jun 19 – Aug 7 | 50–60 |
| Caraway | Mar 20 | Apr 24 | Apr 24 | — | 365–450 |
| Catnip | — | — | May 8 | Jul 10 – Sep 11 | 60–80 |
| Chamomile | Mar 20 | Apr 24 | Apr 24 | Jun 26 – Sep 4 | 60–90 |
| Chervil | Mar 20 | Apr 24 | Apr 24 | Jun 5 – Aug 7 | 40–60 |
| Chives | — | — | May 8 | Jul 10 – Sep 18 | 60–90 |
| Cilantro | Mar 20 | Apr 24 | Apr 24 | Jun 5 – Aug 7 | 40–60 |
| Comfrey | — | — | May 8 | Jul 10 – Sep 18 | 60–90 |
| Dill | Mar 20 | Apr 24 | Apr 24 | Jun 5 – Aug 7 | 40–60 |
| Echinacea | — | — | May 8 | Sep 11 – Oct 2 | 120–180 |
| Fennel (herb) | Mar 20 | Apr 24 | Apr 24 | Jun 26 – Sep 4 | 60–90 |
| Garlic Chives | — | — | May 8 | Jul 10 – Sep 18 | 60–90 |
| Horehound | — | — | May 8 | Jul 24 – Sep 18 | 75–90 |
| Hyssop | — | — | May 8 | Jul 17 – Sep 18 | 70–90 |
| Lemon Balm | — | — | May 8 | Jul 10 – Aug 28 | 60–70 |
| Lovage | — | — | May 8 | Jul 17 – Sep 18 | 70–90 |
| Mint | — | — | May 8 | Jul 10 – Sep 18 | 60–90 |
| Oregano | — | — | May 8 | Jul 10 – Sep 18 | 60–90 |
| Parsley | Mar 20 | Apr 24 | Apr 24 | Jun 26 – Aug 28 | 60–80 |
| Rue | — | — | May 8 | Jul 17 – Sep 18 | 70–90 |
| Sage | — | — | May 8 | Jul 24 – Sep 18 | 75–90 |
| Savory | — | — | May 8 | Jul 3 – Aug 28 | 50–70 |
| Sorrel | Mar 20 | Apr 24 | Apr 24 | Jun 5 – Aug 7 | 40–60 |
| Tarragon | — | — | May 8 | Jul 10 – Sep 18 | 60–90 |
| Thai Basil | Mar 6 | May 8 | May 22 | Jul 17 – Sep 18 | 50–75 |
| Thyme | — | — | May 8 | Jul 17 – Sep 18 | 70–90 |
| Valerian | — | — | May 8 | Sep 11 – Oct 2 | 120–180 |
| Yarrow | — | — | May 8 | Aug 7 – Oct 2 | 90–120 |
Monthly Planting Guide for O'Brien County
Gardening Guides & Resources
Helpful guides from The Ultimate Homestead to improve your garden in O'Brien County.
Frequently Asked Questions
What planting zone is O'Brien County, IA?
O'Brien County is in USDA Hardiness Zone 4b. This zone classification determines which perennial plants survive winter and sets the baseline for frost timing across the county.
When is the last frost in O'Brien County, IA?
Based on 31 years of NOAA weather station data, the median last spring frost in O'Brien County falls around May 1. In 8 out of 10 years, last frost lands between April 17 and May 15 — a 27-day window of variability. Use May 15 as your conservative safe-to-plant date for frost-sensitive crops.
When is the first fall frost in O'Brien County, IA?
The median first fall frost in O'Brien County arrives around October 5. In cold years it can arrive as early as September 20; in mild years as late as October 18. Harvest or protect frost-sensitive crops — tomatoes, peppers, basil, squash — before this date.
How long is the growing season in O'Brien County?
O'Brien County has a frost-free growing season of approximately 157 days. This is enough time for most warm-season crops including tomatoes, peppers, and squash with proper timing.
What is the soil like in O'Brien County for gardening?
O'Brien County has predominantly Silt Loam soil with a pH range of 5.8–7.2 and Well Drained drainage. Most vegetables and herbs grow well with standard composting and seasonal soil amendment.
What is grown commercially in O'Brien County?
O'Brien County has commercial agriculture that includes Soybeans, Corn, Hay, Oats. These crops reflect the local climate and soil conditions — what succeeds commercially often translates well to home gardens in the same area.
Is O'Brien County a good location for home gardening?
O'Brien County scores 75/100 (Good) on our Microclimate Index, which combines frost reliability, drought pressure, soil challenge, elevation risk, and long-term climate trend. This is an above-average location for home gardening with relatively predictable growing conditions.
Plan Your Garden with Confidence
Get our free Garden Planner — designed to help O'Brien County gardeners in Zone 4b organize planting dates, track what's growing, and never miss a planting window.
Get Your Free Garden Planner →Free download. Plan your entire garden season in minutes.
