Planting Guides

When to Plant Onions in Anchorage: Complete Guide + Best Varieties for Zone 4b

Anchorage, Alaska

USDA Zone 4b

Last Frost: May 20

Last updated: December 8, 2025

Plant onions in Anchorage from late April through mid-May using long-day varieties like Walla Walla and Red Wing for Alaska's extreme daylight hours.

TTom Erikson

December 8, 2025

Onion transplants growing in Anchorage garden with Alaska mountains in background during May planting season — — Image © PlantReference.org 2026

Quick Answer

Plant onions in Anchorage from April 25 through May 15 using extreme long-day varieties. Only varieties requiring 15-16+ hours trigger bulbing properly.

TL;DR

Plant onions in Anchorage from late April through mid-May using long-day varieties that trigger bulbing at 14-16+ hours of daylight. Only Allium cepa 'Walla Walla' and similar extreme long-day cultivars will form proper bulbs in Alaska's unique photoperiod. Start with transplants or small sets for best results in the short 118-day growing season.

Frequently Asked Questions

When exactly should I plant onions in Anchorage, Alaska?

Plant onions in Anchorage from April 25 through May 15, depending on soil conditions. Soil temperature should reach 40°F (4°C) before planting. Due to Alaska's short 118-day growing season, avoid planting after mid-May as insufficient time remains for proper bulb development before the September 14 first frost date.

What onion varieties work best in Alaska's extreme daylight hours?

Only extreme long-day varieties work in Alaska. Allium cepa 'Walla Walla', Allium cepa 'Red Wing', and Allium cepa 'Yellow Sweet Spanish' trigger bulbing at 15-16+ hours of daylight. Standard long-day varieties requiring only 14 hours won't form bulbs in Alaska's nearly 20-hour summer days.

Can I grow garlic successfully in Anchorage's harsh winters?

Yes, hardneck garlic thrives in Alaska. Plant Allium sativum 'Music' or Allium sativum 'German Extra Hardy' in September for August harvest. These varieties require the 4-8 weeks below 40°F that Alaska provides naturally. Apply 6-8 inches of mulch for winter protection.

Why do my onions stay small even with healthy green tops?

This indicates a day-length mismatch—the most common Alaska onion problem. Varieties requiring fewer than 15 hours of daylight trigger bulbing too early before developing sufficient leaf area. Only plant extreme long-day varieties specifically bred for northern latitudes above 60°N.

How do I cure and store onions in Alaska's cool, humid climate?

Use heated indoor spaces for curing rather than outdoor methods. Garages, basements, or greenhouses at 75-85°F with fans for air circulation work best. Curing takes 3-4 weeks in Alaska conditions. Store cured onions at 32-40°F in ventilated containers for 8-10 months with proper varieties.

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Tagged with

#when to plant onions anchorage #alaska onion growing #zone 4b onions #long day onions #walla walla onions #alaska gardening #anchorage planting dates #cold climate onions #extreme photoperiod onions #alaska garlic planting

Written By

Tom Erikson

Tom is a lifelong Alaskan who gardens in Anchorage, where the growing season is short but intense. He works for the state cooperative extension service and has spent years figuring out what works in a climate where the ground freezes deep, the growing season starts in late May, and you get 19 hours of daylight in June. Tom grows cold-hardy vegetables, maintains a collection of boreal-adapted perennials, and experiments with season extension using cold frames and row covers. He writes about the realities of northern gardening—the unique advantages (those long summer days produce remarkable growth) and the genuine limitations. Tom's tone is calm and practical, with the quiet humor of someone who's gardened through Alaskan winters for decades.