Planting Guides

When to Plant Kale in Boston: Complete Guide + Best Varieties for Zone 6b

Boston, Massachusetts

USDA Zone 6b

Last Frost: Apr 20

Last updated: October 30, 2025

Learn when to plant kale in Boston with specific dates for Zone 6b. Compare 5 varieties & discover which kale grow best in Massachusetts climate.

DDorothy "Dot" Williams

October 30, 2025

Kale plants growing in Boston Zone 6b garden with urban skyline — — Image © PlantReference.org 2025

Quick Answer

Plant kale in Boston March 15-22 for spring harvest, July 15-August 8 for fall. Fall crops taste superior after frost sweetening.

TL;DR

Plant kale in Boston March 15-22 for spring harvest and July 15-August 8 for superior fall crops. Fall planting produces sweeter kale due to frost exposure. Boston's Zone 6b climate allows Brassica oleracea 'Winterbor' to overwinter with protection, providing harvest through January.

Product Recommendations

Burpee Winterbor Kale Seeds

($3.95-4.95)— Extremely cold-hardy variety perfect for Boston overwintering

Burpee Winterbor F1 Hybrid Kale Seeds

https://www.burpee.com/vegetables/kale/kale-winterbor-f1-hybrid-prod000862.html

Winterbor F1 hybrid delivers exceptional cold tolerance for Boston Zone 6b winters. Deeply curled blue-green leaves develop incredible sweetness after frost exposure. Plants reach 18-24 inches tall with excellent uniformity. Matures in 60-75 days with superior bolt resistance. Overwinters reliably with row cover protection down to 10°F. Perfect choice for extending Boston harvest through January and February.

Price: $3.95-4.95

Johnny's Seeds Lacinato Kale

($3.25-4.25)— Premium heirloom variety with exceptional flavor after Boston frosts

Johnny's Selected Seeds Lacinato Kale Organic

https://www.johnnyseeds.com/vegetables/greens/kale/lacinato-kale-seed-508.html

Certified organic Lacinato kale produces distinctive flat, strap-like leaves with savoyed texture. Italian heirloom variety develops exceptional nutty sweetness after October frost exposure in Boston. Plants grow 24-30 inches tall with consistent harvest potential. Excellent heat tolerance for spring planting and superior cold tolerance for fall crops. Easier to clean than curly varieties, making harvest processing more efficient for busy Boston gardeners.

Price: $3.25-4.25

Agribon AG-15 Floating Row Cover

($24.95-34.95)— Essential protection for Boston's variable spring weather

Agribon AG-15 Lightweight Floating Row Cover 10ft x 20ft

https://www.gardeners.com/buy/agribon-row-cover/8593456.html

Lightweight spun fabric provides 4-6°F temperature protection during Boston spring cold snaps while allowing 85% light transmission. Protects young kale plants from cabbage white butterflies and flea beetles without pesticide applications. Easy installation over hoops or direct plant contact. Breathable fabric prevents overheating during sunny April days. Extends fall harvest 4-6 weeks past first frost when properly secured. Essential tool for season extension in Boston's Zone 6b climate.

Price: $24.95-34.95

Peaceful Valley Complete Organic Fertilizer

($16.95-19.95)— Balanced nutrition for sustained kale production

Peaceful Valley Complete Organic Fertilizer 4-4-4 (4 lb)

https://www.groworganic.com/complete-organic-fertilizer-4-4-4.html

Slow-release 4-4-4 blend provides balanced nutrition for vigorous kale growth throughout Boston's 183-day growing season. Contains kelp meal, feather meal, and rock phosphate for sustained feeding without burn risk. Apply at planting and side-dress after 6 weeks for continuous harvest. Improves soil biology supporting healthier plants with better pest resistance. OMRI-listed organic formula safe for edible crops and beneficial insects.

Price: $16.95-19.95

DeWit Harvest Knife

($28.95-32.95)— Sharp, ergonomic tool for clean kale leaf cutting

DeWit Right-Handed Harvest Knife with Serrated Edge

https://www.johnnyseeds.com/tools-supplies/harvesting-tools/knives/dewit-right-handed-harvest-knife-9950.html

Hand-forged carbon steel blade maintains razor sharpness for clean cuts that promote continued kale production. Ergonomic ash wood handle reduces hand fatigue during extended harvest sessions. Serrated edge cuts tough kale stems without damaging plants. Compact 6-inch blade perfect for precision work in dense Boston garden beds. Traditional Dutch craftsmanship provides decades of reliable service. Clean cuts heal faster, reducing disease entry points.

Price: $28.95-32.95

Frequently Asked Questions

When should I start kale seeds indoors in Boston?

Start kale seeds indoors February 15-March 1 for spring planting and June 15-July 1 for fall planting. Indoor starting provides 6-8 week old transplants ready for outdoor planting when conditions are optimal. Spring transplants go outside March 22-April 5, while fall transplants move outdoors August 1-15. This timing avoids the stress of direct sowing during Boston's variable spring weather or hot summer conditions.

Can kale survive Boston winters outdoors?

Brassica oleracea 'Winterbor' survives Boston winters with protection. Use row covers or cold frames when temperatures drop below 20°F (-7°C). Plants go dormant during January and February but resume growth in March. Mulch heavily around plant bases to prevent frost heaving. Coastal areas of Boston have better survival rates due to ocean moderation of temperature extremes.

Why does my Boston kale bolt in spring but not fall?

Spring bolting occurs because kale experiences vernalization—cold exposure followed by warming temperatures triggers flowering. Boston's cool April followed by warm May mimics the plant's natural two-year cycle. Fall plantings develop as temperatures drop, avoiding the cold-then-warm sequence. Additionally, fall kale benefits from decreasing daylight hours which suppress flowering hormones. Plant Brassica oleracea 'Vates' for best spring bolt resistance.

What's the best kale variety for small Boston gardens?

Brassica oleracea 'Vates' works perfectly for Boston container gardening and small spaces. This dwarf variety reaches only 12-16 inches tall while producing abundantly. It tolerates Boston's urban heat island effect better than tall varieties and fits in 12-inch deep containers. Space plants 8-10 inches apart in small beds compared to 12 inches for full-size varieties. Brassica oleracea 'Red Russian' also works well due to its upright, narrow growth habit.

How do I know when Boston kale is ready to harvest?

Harvest kale leaves when they reach 6-8 inches long, typically 6-8 weeks after planting. Brassica oleracea 'Red Russian' matures fastest at 50-60 days, while Brassica oleracea 'Winterbor' takes 60-75 days. For sweetest flavor, harvest after Boston's first frost (around October 19) when cold exposure converts starches to sugars. Leaves should feel crisp and show deep color—avoid yellowing or tough, fibrous leaves which indicate overmaturity.

Should I remove kale flowers if the plant bolts?

Remove flower stalks immediately when Boston kale bolts to redirect energy into leaf production. Cut flowering stems at the base using sharp garden shears. However, once kale bolts, leaf quality declines significantly—they become bitter and tough. Consider harvesting flower buds and young flowers as "kale raab" for stir-fries. Plant Brassica oleracea 'Winterbor' for better bolt resistance in Boston's variable spring weather.

What spacing works best for kale in Boston raised beds?

Space kale plants 12 inches apart in all directions in Boston raised beds. This spacing provides adequate air circulation to prevent fungal diseases common in Boston's humid conditions while maximizing production. For Brassica oleracea 'Vates' dwarf variety, use 8-10 inch spacing. Closer spacing increases disease pressure and reduces individual plant size, while wider spacing wastes valuable Boston garden space. Row spacing of 18 inches allows easy access for harvesting and maintenance.

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Tagged with

#kale planting boston #zone 6b gardening #when to plant kale #boston vegetable garden #massachusetts gardening #winterbor kale #lacinato kale #fall kale planting #cold hardy vegetables #boston frost dates

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."