When to Plant Onions in Portland: Complete Guide + Best Varieties for Zone 8b

Living in Portland for forty years, I've learned that our Zone 8b climate gives us something most gardeners envy—the ability to plant onions twice a year. While folks in Minnesota are limited to spring planting, we can choose between spring planting for fall harvest or fall planting for an early summer harvest.

Best Onion Varieties for Portland's Climate

Portland sits at 45°N latitude, which means we need long-day onion varieties that require 14-16 hours of daylight to trigger bulbing. This is crucial—plant short-day varieties here and you'll get giant green tops but no bulbs.

The magic happens during our long June and July days when the sun doesn't set until after 9 PM. That extended daylight signals long-day onions to stop making leaves and start forming bulbs.

Here are the varieties that consistently perform well in Portland's climate:

Walla Walla Sweet is our regional champion. Developed just 260 miles east of us, it's perfectly adapted to Pacific Northwest conditions. The sweet, mild flavor comes from our naturally low-sulfur soils.

Red Wing gives you the longest storage life—I've had properly cured Red Wing onions last until the following August. That's nearly a full year of onion storage from one planting.

For garlic, Portland gardeners have excellent options with both hardneck and softneck varieties:

🌿Allium sativum 'Music' is the hardneck standard for our area. Plant cloves in October, harvest in July. The large bulbs have 4-6 jumbo cloves with complex flavor.

🌿Allium sativum 'California Early' softneck stores longer and braids beautifully. It's more heat-tolerant for our occasional hot summers.

Specific Planting Dates for Portland

Portland's last frost averages March 19, but I've been tracking it for decades—we can often plant earlier because our soil drains well and warms quickly.

Spring Planting Schedule

March 1-15: Onion Sets and Transplants Plant as soon as soil is workable. Onions are cold-hardy and actually prefer cool weather for establishing roots. I aim for soil temperature of 35°F (2°C) or warmer.

March 15-April 1: Direct Seeding If you're growing from seed, wait until soil reaches 40°F (4°C). Seeds germinate slowly in cold soil but won't rot if drainage is good.

Harvest Timeline for Spring Planting:

• Early varieties: Late July to early August

• Main season: August through September

• Storage varieties: September when tops fall naturally

Fall Planting Schedule (Advanced Technique)

This is where Portland gardeners gain a real advantage. Fall planting gives you earlier harvest, larger bulbs, and fewer pest problems.

October 15-30: Transplant Only Use only transplants for fall planting—never sets or seeds. The young plants need time to establish roots before winter but shouldn't get too large or they'll bolt in spring.

Overwintering Management:

• Mulch with 2 inches (5 cm) of straw in December

• Expect some winter leaf die-back—normal in Zone 8b

• Remove mulch in March when growth resumes

• Side-dress with compost in early April

Harvest Timeline for Fall Planting:

• Early varieties: May through June

• Main season: June through July

• Advantage: Harvest before summer heat stress

Garlic Planting Dates

October 1-15: Hardneck Varieties Plant 🌿Allium sativum 'Music' and other hardnecks early to ensure adequate cold exposure for proper bulb development.

October 15-November 1: Softneck Varieties 🌿Allium sativum 'California Early' can be planted later since it requires less vernalization.

Plant individual cloves 2 inches (5 cm) deep, 6 inches (15 cm) apart, pointed end up. In Portland's climate, both types will be ready to harvest by mid-July.

Complete Growing Guide for Portland

Soil Preparation

Portland's heavy clay soils need amendment for successful onion growing. I always add 2-3 inches (5-8 cm) of compost before planting.

pH Requirements: Onions prefer 6.0-6.8 pH. Most Portland soils run slightly acidic, so lime application every 2-3 years helps maintain optimal pH.

Drainage is Critical: Our wet winters can cause bulb rot. Raised beds or mounded rows improve drainage significantly. Even 4 inches (10 cm) of elevation makes a difference.

• Test soil pH in February—add lime if below 6.0

• Work in 3 inches (8 cm) of compost each spring

• Create raised rows if your garden has drainage issues

• Add coarse sand to heavy clay areas (not fine sand)

• Ensure 6+ hours direct sunlight daily

Fertilization Strategy

Onions are heavy nitrogen feeders early in the season but need phosphorus and potassium for bulb development.

Pre-Planting: Work 2-3 inches (5-8 cm) of aged compost into beds. This provides slow-release nutrients throughout the growing season.

Growing Season Feeding:

• Apply balanced 10-10-10 fertilizer at planting

• Side-dress with compost tea every 3 weeks through May

• Stop all nitrogen feeding by June 15—late nitrogen delays maturity

• Apply potassium sulfate in early June to improve storage quality

Critical Timing: Stop nitrogen applications when bulbing begins. You'll know bulbing has started when the soil cracks around the base of the plant.

Watering Guidelines

Portland's wet winters and dry summers create unique watering challenges for onions.

Spring Management (March-May): Usually no supplemental watering needed. Our spring rains typically provide adequate moisture.

Summer Management (June-September): Deep watering once or twice weekly. Onions need consistent moisture but hate waterlogged soil.

Pre-Harvest (August-September): Reduce watering as tops begin to yellow. Stop watering completely 2 weeks before harvest to encourage proper curing.

Pest Management for Portland

Our mild, moist climate creates perfect conditions for certain onion pests.

Onion Root Maggot is our biggest challenge. The flies lay eggs at the base of plants in May, and larvae tunnel into developing bulbs.

• Use floating row covers from planting through May

• Delay planting until after May 1 to avoid peak egg-laying

• Remove all onion family debris each fall

• Rotate planting areas—don't grow onions in the same spot two years running

Thrips damage leaves and can transmit viruses. Look for silvery streaks on foliage.

• Overhead watering knocks thrips off plants

• Blue sticky traps placed near plants catch adult thrips

• Beneficial insects like lacewings help control thrips naturally

Downy Mildew appears as fuzzy growth on leaves during our wet springs.

• Improve air circulation with proper spacing

• Water at soil level, not on foliage

• Remove affected leaves immediately

• Plant in full sun locations that dry quickly after rain

Troubleshooting Portland-Specific Problems

Problem: Small Bulbs Despite Good Growth

This is usually a variety selection issue. If you planted intermediate-day or short-day varieties, they won't bulb properly in Portland's latitude.

Solution: Only plant long-day varieties that need 14-16 hours of daylight. Save the 'Texas Sweet' and 'Granex' varieties for friends in California.

Problem: Onions Bolting (Going to Seed)

Bolting destroys the bulb and makes onions inedible. In Portland, this usually happens with fall-planted onions that grew too large before winter.

Solutions:

• Plant transplants in late October, not early October

• Choose smaller transplants (pencil thickness or less)

• Provide consistent moisture—drought stress triggers bolting

• Avoid large onion sets which bolt more readily

Problem: Thick Necks That Won't Cure

Onions with thick, fleshy necks won't store properly and tend to rot quickly.

Causes and Solutions:

• Too much nitrogen late in season—stop feeding by June 15

• Excessive watering near harvest—reduce water as tops yellow

• Harvesting too early—wait for natural top fall-over

• Wrong variety for storage—choose 'Copra' or 'Red Wing' for long storage

Problem: Poor Winter Survival of Fall-Planted Onions

Some winters are harder than others in Zone 8b. The 2021 ice storm taught many Portland gardeners about winter protection.

Solutions:

• Mulch with 3-4 inches (8-10 cm) of straw in December

• Choose cold-hardy varieties like 'Walla Walla' for fall planting

• Plant in protected locations away from north wind

• Use low tunnels or cold frames during extreme cold snaps below 20°F (-7°C)

Harvest & Storage

Determining Harvest Readiness

Harvest timing is crucial for storage quality. I wait until 50-75% of the tops fall over naturally. This indicates the plant has finished moving sugars from the leaves into the bulb.

Never bend tops over manually—this creates wounds that invite rot and reduces storage life.

Harvest Process

Choose a dry day for harvest. Portland's late summer usually provides several clear days perfect for onion harvest.

• Lift bulbs carefully with garden fork, don't pull

• Brush off soil but don't wash

• Leave roots and tops attached initially

• Lay in single layer in sunny, well-ventilated area

Curing for Storage

Portland's humid climate makes proper curing critical. I use my garage with fans running for air circulation.

Curing Process:

• Spread onions in single layers on screens or mesh trays

• Provide good airflow—use fans if necessary

• Maintain temperature around 80-85°F (27-29°C) for fastest curing

• Cure for 2-4 weeks until outer skins are papery

• Necks should feel completely dry and tight

Storage Conditions: Once cured, store at 32-40°F (0-4°C) with 60-70% humidity. A cool basement or garage works well in Portland's climate.

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