Planting Guides

When to Plant Kale in Boise: Complete Guide + Best Varieties for Zone 6a

Boise, Idaho

USDA Zone 6a

Last Frost: May 5

Last updated: October 30, 2025

Plant kale in Boise April 1-15 for spring harvest or August 1-15 for superior fall crops in Zone 6a's 158-day season.

DDorothy "Dot" Williams

October 30, 2025

When to plant kale in Boise Idaho - thriving kale varieties in Zone 6a garden with mountain backdrop — — Image © PlantReference.org 2025

Quick Answer

Plant kale in Boise April 1-15 for spring harvest or August 1-15 for fall crops. Fall plantings develop superior flavor after frost.

TL;DR

Plant kale in Boise April 1-15 for spring crops or August 1-15 for superior fall harvests in Zone 6a. Fall plantings survive Idaho's winters and develop the sweetest flavor after frost. Choose Brassica oleracea 'Winterbor' for maximum cold hardiness or Brassica oleracea 'Lacinato' for tender leaves and excellent flavor.

Product Recommendations

Burpee Winterbor Kale Seeds

($3-4)— Extremely cold hardy F1 hybrid perfect for Boise winters

Burpee Winterbor Kale Seeds - F1 Hybrid Cold Hardy Variety

https://www.burpee.com/vegetables/kale/kale-winterbor-prod000448.html

Winterbor F1 hybrid kale delivers exceptional cold hardiness for Zone 6a conditions, surviving temperatures to 5°F with light protection. Deep blue-green, heavily savoyed leaves grow on compact 18-inch plants ideal for Boise's windy conditions. This variety sweetens dramatically after frost exposure, making it perfect for fall planting and winter harvest. Slow to bolt in spring temperature swings, providing reliable production through variable weather. Excellent choice for overwintering in cold frames or under row covers.

Price: $3.49-$4.29

Johnny's Seeds Lacinato Kale

($4-5)— Heat-tolerant heirloom ideal for Boise's temperature extremes

Johnny's Seeds Lacinato Kale - Organic Heirloom Dinosaur Kale

https://www.johnnyseeds.com/vegetables/kale/lacinato-kale-seed-324.html

Lacinato kale offers superior heat tolerance and tender texture ideal for Boise's challenging growing conditions. Dark blue-green, heavily savoyed strap-like leaves lack the bitterness common in curly varieties. This Italian heirloom resists bolting better than most kales during May temperature swings, extending spring harvest window. Grows 24-30 inches tall with excellent uniformity. Easy to clean flat leaves shed dust better than curly types—important in Boise's windy high desert environment. Outstanding for both fresh eating and cooking applications.

Price: $3.95-$4.95

Southern Exposure Red Russian Kale Seeds

($3-4)— Fast-maturing variety perfect for succession planting

Southern Exposure Red Russian Kale Seeds - Open Pollinated Hardy Variety

https://www.southernexposure.com/products/kale-red-russian/

Red Russian kale matures in just 50-60 days, making it perfect for Boise's succession planting strategy and quick spring harvests before summer heat. Distinctive flat, oak-leaf shaped foliage features purple veins that intensify in cold weather. This open-pollinated variety handles temperature fluctuations better than many hybrids, ideal for Boise's unpredictable spring weather. Tender leaves work excellently for baby kale harvest at 30 days or full-size harvest later. Sweet, mild flavor improves significantly after frost exposure, making it outstanding for fall planting.

Price: $2.95-$3.95

High Mowing Redbor Kale Seeds

($4-5)— Ornamental cold-hardy variety with exceptional flavor

High Mowing Redbor Kale Seeds - Organic F1 Purple Kale Hybrid

https://www.highmowingseeds.com/products/kale-redbor

Redbor F1 hybrid combines exceptional cold hardiness with stunning deep purple color that intensifies through Boise's fall and winter. Tall, upright plants reach 24-30 inches with deeply curled, frilly leaves that create beautiful texture in winter gardens. Cold tolerance equals Winterbor while offering superior flavor—sweet and crisp without bitterness. Purple pigmentation provides additional antioxidants and UV protection for plant tissues. Excellent fresh eating quality even in winter, making it ideal for continuous harvest through cold frames or row covers.

Price: $4.25-$5.25

Territorial Vates Kale Seeds

($3-4)— Compact dwarf variety ideal for containers and windy conditions

Territorial Seed Vates Kale - Dwarf Blue Curled Open Pollinated

https://territorialseed.com/products/kale-vates

Vates dwarf kale grows just 12-16 inches tall, making it perfect for Boise's windy conditions and container gardening. This open-pollinated variety shows remarkable bolt resistance during temperature swings, providing reliable harvest through spring heat-ups and fall cooling. Compact blue-green plants produce tender, finely curled leaves with excellent eating quality. Slow to bolt characteristics extend harvest window significantly compared to taller varieties. Outstanding choice for small spaces, urban gardens, and areas with limited protection from wind. Consistent performer across varying growing conditions.

Price: $2.95-$3.95

Frequently Asked Questions

When should I plant kale in Boise for the best flavor?

Plant kale in Boise between August 1-15 for fall harvest. Fall-planted kale develops superior flavor because Idaho's first frost around October 9th converts starches to sugars, creating sweet, tender leaves. Spring plantings (April 1-15) work well but lack the frost-enhanced sweetness that makes fall kale exceptional. The gradual cooling temperatures and increased rainfall in fall create ideal growing conditions that spring plantings often struggle to match.

Which kale varieties handle Boise's Zone 6a winters best?

Brassica oleracea 'Winterbor' and Brassica oleracea 'Redbor' are your most reliable winter survivors in Boise. Both handle temperatures down to 5°F (-15°C) with light row cover protection. Brassica oleracea 'Vates' also overwinters well and stays compact in windy conditions. Brassica oleracea 'Red Russian' may suffer damage below 15°F (-9°C) but recovers quickly. Brassica oleracea 'Lacinato' is moderately hardy but benefits from cold frame protection during January and February cold snaps.

Can I grow kale during Boise's hot summers?

Summer kale production in Boise requires careful variety selection and management. Brassica oleracea 'Lacinato' handles heat better than curly types and may survive with afternoon shade and consistent irrigation. Most varieties bolt (flower and turn bitter) when temperatures consistently exceed 80°F (27°C), typically mid-July through August. Focus on spring harvest finishing by July 1st, then plant fall crops in August for better results. Summer success requires daily watering, shade cloth, and accepting lower leaf quality.

How do I prevent cabbage worms on my Boise kale plants?

Cabbage worms are the white butterfly larvae that create large holes in kale leaves. In Boise, use floating row covers immediately after planting spring crops to exclude egg-laying adults. Remove covers once plants are established (4-6 weeks). For uncovered plants, spray with Bt (Bacillus thuringiensis) weekly during active butterfly periods (May-June and August-September). Hand-picking works for small gardens—check plants every 2-3 days and remove green caterpillars. Fall plantings typically have fewer problems as butterfly activity decreases with cooling temperatures.

What soil amendments work best for kale in Boise's alkaline soil?

Boise's alkaline soil (pH 7.5-8.5) needs organic matter and slight acidification for optimal kale production. Add 2-3 inches of compost annually to improve soil structure and buffer pH. Apply sulfur at 1 pound per 100 square feet in spring to gradually lower pH to 6.5-7.0. Bone meal provides phosphorus and calcium, while kelp meal supplies trace minerals often lacking in Idaho soils. Mycorrhizal inoculant helps establish strong root systems in our mineral-rich but biologically poor volcanic soils. Avoid lime—our soils are already too alkaline.

How long can I harvest kale through Boise's winter?

With proper protection, kale harvest can continue through February in most Boise winters. Brassica oleracea 'Winterbor' and Brassica oleracea 'Redbor' survive under row covers or in cold frames when temperatures drop below 15°F (-9°C). Snow actually insulates plants, allowing harvest by brushing snow away. January and February provide the sweetest leaves as cold temperatures maintain high sugar content. Harvest during warmer periods (above 25°F/-4°C) to prevent leaf damage. Plan for 2-4 month winter harvest period depending on variety and protection methods used.

Should I start kale from seeds or transplants in Boise?

Both methods work well in Boise, but timing determines the best approach. For spring planting, start seeds indoors March 15-22 and transplant April 10-20, or direct sow April 1-15 when soil reaches 45°F (7°C). Fall plantings work best as direct seeding August 1-15, allowing full season growth in ideal conditions. Direct seeding costs less and avoids transplant shock, while transplants give you a head start and better control over spacing. In Boise's clay soils, cover seeds with vermiculite rather than native soil to prevent crusting that blocks seedling emergence.

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Written By

Dorothy "Dot" Williams

Dot grew up on a small farm in rural Virginia and has maintained a vegetable garden for decades. After retiring from teaching elementary school, she became a Master Gardener volunteer and spends her time mentoring new gardeners at community garden plots in Richmond. She's especially knowledgeable about heirloom varieties, seed saving, and traditional growing methods passed down from her grandmother. Dot's no-nonsense advice comes from extensive trial and error—she's seen every tomato disease, pest problem, and weather disaster imaginable. Her biggest pet peeve is gardeners who overcomplicate simple tasks. "Plants want to grow," she often says. "Your job is to not get in their way."