Planting Guides

When to Plant Onions in Boston: Complete Guide + Best Varieties

Boston, Massachusetts

USDA Zone 6b

Last Frost: Apr 20

Last updated: December 8, 2025

Plant onions in Boston April 5-26 for Zone 6b success. Learn long-day varieties, exact timing, and complete growing guide for Massachusetts gardeners.

DDorothy "Dot" Williams

December 8, 2025

When to plant onions in Boston - onion transplants in garden bed with Boston skyline background — — Image © PlantReference.org 2025

Quick Answer

Plant onions in Boston April 5-26 when soil reaches 50°F consistently. Use long-day varieties for Zone 6b success.

TL;DR

Plant onions in Boston from April 5-26 using long-day varieties like Allium cepa 'Walla Walla' for Zone 6b success. Plant garlic cloves October 15-November 5 for next summer's harvest. Boston's 183-day growing season and 42°N latitude require long-day onion varieties that bulb when daylight reaches 14+ hours in late June.

Product Recommendations

Walla Walla Sweet Onion Sets

($12-18)— Perfect long-day variety for Boston's latitude

Walla Walla Sweet Onion Sets - 1 lb bag

https://www.burpee.com/vegetables/onions/onion-sets-walla-walla-sweet-prod001234.html

Premium quality dormant onion sets selected for Boston's Zone 6b climate. These long-day sets produce sweet, mild onions perfect for fresh eating through late summer. Each set is sized smaller than a dime to prevent bolting issues common with large sets. Plant April 5-26 for best results in Massachusetts. Produces bulbs 4-5 inches across when grown in amended soil with consistent moisture.

Price: $12.95-$17.95

Red Wing Storage Onion Plants

($14-22)— Best storage variety for Boston winters

Red Wing F1 Hybrid Onion Transplants - 60 count

https://dixondalefarms.com/product/redwing-onion-plants/

Professional-grade onion transplants specifically grown for long-term storage in New England climates. Red Wing produces deep red bulbs with excellent keeping quality, storing 8-10 months when properly cured. Disease-certified transplants establish quickly in Boston's clay soil. These long-day onions suit Massachusetts latitude and develop intense flavor ideal for cooking. Plant 1 inch deep, 4 inches apart for maximum bulb development.

Price: $14.50-$21.95

Music Hardneck Garlic Bulbs

($16-24)— Premium hardneck variety for Zone 6b

Music Garlic Bulbs for Planting - 1/2 lb

https://www.groworganic.com/products/music-garlic-bulbs

Music hardneck garlic produces large bulbs with 4-6 jumbo cloves, perfectly adapted to Boston's Zone 6b winters. This porcelain-type garlic requires cold vernalization making it ideal for Massachusetts fall planting. Plant cloves October 15-November 5, harvest July for maximum bulb size. Excellent storage life (6-9 months) and complex flavor ranging from spicy when raw to sweet when roasted. Each bulb weighs 2-3 ounces with tight, white wrapper skins.

Price: $16.95-$23.95

Onion Storage Mesh Bags

($8-15)— Essential for proper Boston storage conditions

Produce Storage Mesh Bags - Set of 6

https://www.amazon.com/dp/B087QRSTUVW

Heavy-duty mesh bags designed for long-term onion storage in basement conditions typical of Boston homes. Allows proper air circulation while protecting from light exposure that causes sprouting. Each bag holds 10-15 pounds of cured onions with drawstring closure for easy handling. Machine washable and reusable for multiple seasons. Essential for storing Red Wing and other storage varieties through Massachusetts winters in 32-40°F basements or garages.

Price: $8.95-$14.95

Soil Thermometer for Spring Planting

($12-18)— Know exactly when to plant in Boston

Long Stem Soil Thermometer - 8 inch probe

https://www.johnnyseeds.com/tools-supplies/thermometers/soil-thermometer-7147.html

Professional-grade soil thermometer with 8-inch stainless steel probe for accurate temperature readings in Boston's variable spring conditions. Large, easy-read dial shows precise temperatures from 20-180°F. Essential for timing onion planting when soil reaches consistent 50°F in early April. Durable construction withstands repeated use in clay soil conditions typical of Boston area. Includes protective sheath and care instructions for season-long accuracy.

Price: $12.50-$17.95

Frequently Asked Questions

When exactly should I plant onions in Boston?

Plant onions in Boston from April 5-26 when soil temperature reaches 50°F consistently. This timing allows 2-3 weeks before the average last frost date of April 19th while giving onions the full growing season needed for proper bulb development. Planting earlier in cold, wet soil leads to rot; planting later reduces final bulb size as day length triggers bulbing in late June regardless of planting date.

What onion varieties grow best in Boston's Zone 6b climate?

Long-day varieties are essential for Boston's 42°N latitude and Zone 6b climate. Allium cepa 'Walla Walla' produces sweet, large bulbs perfect for fresh eating through late summer. Allium cepa 'Red Wing' develops into excellent storage onions lasting 8+ months when properly cured. Allium cepa 'Yellow Sweet Spanish' creates the largest bulbs, often exceeding one pound with proper care. Never plant short-day varieties in Boston—they won't form bulbs in our latitude.

Can I plant onions in fall in Boston?

Fall onion planting is not recommended for Boston gardeners growing bulb onions. Boston's Zone 6b climate lacks the mild winters necessary for overwintering onion varieties. However, fall garlic planting is essential—plant Allium sativum 'Music' or Allium sativum 'California Early' cloves from October 15-November 5 for next summer's harvest. Garlic requires winter cold exposure to form proper cloves and performs best with fall planting.

Why are my Boston onions not forming bulbs?

Onions fail to bulb in Boston due to wrong variety selection or late planting. Short-day and intermediate-day onions won't form bulbs at Boston's 42°N latitude because our summer days (15+ hours) exceed their trigger points. Plant only long-day varieties that require 14-16 hours of daylight to bulb. Late planting after April 26th also reduces bulbing as plants lack sufficient leaf growth before day length triggers the bulbing process in late June.

How do I prepare Boston's clay soil for onions?

Boston's heavy clay soil requires significant amendment for successful onion growing. Work 2-3 inches of compost into the top 8 inches of soil each spring, adding coarse sand (never fine sand) to improve drainage. Build raised rows 4-6 inches high even within raised beds to ensure proper drainage. Test soil pH and add sulfur if above 7.0. Never work clay soil when wet—wait until it crumbles easily in your hand to avoid compaction.

When should I harvest onions in Boston?

Harvest onions in Boston when 50-75% of tops fall over naturally, typically mid-August through early September depending on planting date and variety. Allium cepa 'Red Wing' planted April 10th usually matures by August 25th. Never force tops to fall by stepping on them—this creates wounds that cause storage rot. Bulbs should feel firm when squeezed gently at soil level, with outer skins beginning to develop papery texture.

How do I store onions through Boston winters?

Cure onions first in a warm (75-85°F), dry location with good air circulation for 2-3 weeks until skins are papery and necks tight. Store cured onions in Boston basements or unheated garages that maintain 32-40°F through winter. Use ventilated containers or mesh bags—never plastic. Check monthly and remove any soft bulbs immediately to prevent spoilage spread. Properly cured Allium cepa 'Red Wing' stores 8-10 months in Boston conditions.

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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."