When to Plant Onion in Onaga, Kansas (66521)

Location

Onaga, Kansas

ZIP Code

66521

USDA Zone

Last Frost

Monday, April 20, 2026

📅 Your 2026 Planting Dates

Start Seeds Indoors

Monday, February 23, 2026

Transplant Outdoors

Monday, May 4, 2026

Based on last frost Monday, April 20, 2026 · Zone 6a

Pro tip: Start Onion seeds indoors 8 weeks before your last frost date, then transplant outdoors around Monday, May 4, 2026.

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🌿 Plant Details

Scientific Name Allium cepa

Days to Maturity 100 days

Mature Height 12-18"

Spread 4"

Type Bulb

Fruit Size Medium (2-4 inch bulb)

☀️ Growing Requirements

☀️

Sun

Full Sun (6+ hours)

💧

Water

Moderate

↔️

Spacing

4" apart

🌱

Planting Depth

0.5" deep

Seeds typically germinate in 7-10 days

Ready to Plant Onion in Onaga?

Get your seeds now so they're ready by Monday, February 23, 2026.

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🤝 Good Companions

CarrotBeetLettuceTomatoBrassicas

⚠️ Avoid Planting Near

BeanPeaAsparagus

🤝

Full Companion Planting Guide for Onion

See which plants help Onion thrive, which to keep away, and raised bed layout tips →

🛠️ Supplies You'll Need

🌱 Seed Starting Trays 🪴 Seed Starting Mix 💡 Grow Lights 🌡️ Heat Mat 🪵 Raised Garden Bed 🌍 Vegetable Garden Soil 🛠️ Hand Trowel Set 🚿 Watering Can

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Common Onion Varieties

Popular cultivars to look for at your local nursery or seed supplier.

Yellow Sweet Spanish

yellow 110d

Large, mild onion with golden skin; the most widely grown long-day onion in North America.

Red Burgundy

red 95d

Short-day red onion with mild, sweet flavor; excellent for fresh eating and salads.

Candy

yellow 85d

High-yielding intermediate-day onion with sweet, mild flavor; stores well.

Walla Walla Sweet

yellow 125d

Famous Pacific Northwest sweet onion with very low pungency and high sugar content.

Cipollini

specialty 100d

Small, flat Italian onion with intense sweetness; prized for roasting and caramelizing.

Common Onion Problems

What to watch for — and how to fix it before it spreads.

🐛

Pests

Onion Thrips

Tiny insects rasp leaf surfaces leaving silver streaking; transmit iris yellow spot virus.

Fix:

Apply spinosad or insecticidal soap; use reflective mulch; avoid planting near grass.

Onion Maggot

Fly larvae tunnel into bulbs causing plants to collapse; worst in cool, wet springs.

Fix:

Use row covers; rotate crops far from previous onion beds; till soil to expose pupae to birds.

Wireworm

Soil-dwelling larvae bore small tunnels into developing bulbs.

Fix:

Till deeply before planting; plant buckwheat as a trap crop; use beneficial nematodes.

🍂

Diseases

Botrytis Neck Rot

Gray mold at the neck of stored bulbs; spreads through the bulb in storage.

Fix:

Cure bulbs thoroughly (2–3 weeks in warm, dry, airy space) before storage.

Purple Blotch

Water-soaked white lesions that turn purple; leaves collapse and dry in wet weather.

Fix:

Apply copper fungicide; avoid overhead watering; plant in well-draining soil.

Fusarium Basal Rot

Pink-red discoloration at the base of the bulb; common in hot soils.

Fix:

Rotate crops; improve drainage; plant resistant varieties; avoid injuring bulbs at planting.

💡

Common Mistakes

Wrong day-length variety for your latitude

Short-day onions won't form bulbs in northern regions; long-day varieties stay tiny in the South.

Fix:

Choose long-day varieties (14+ hours) for north of 35°N, short-day for south of 35°N, intermediate for in between.

Planting too deep

Deep-planted sets or transplants have energy diverted away from bulb development.

Fix:

Plant sets or transplants so the top of the bulb/root mass is just at or slightly below soil surface.

🌾 Seed Saving Guide

🟡 Moderate

✅ Open-pollinated — seeds grow true to parent

When to Harvest Seed

Allow seed heads to form in year 2 (onions are biennial). Harvest when most seeds are black and visible.

Processing

Cut seed heads into bags, dry 1 week, shake to release seeds.

Seed Viability

Up to 1 year when stored cool, dark, and dry.

Pro Tip

Onion seed is very short-lived — use within 1 year. Cross-pollinates with other onion varieties via insects.

🪴

Raised Bed Planting Guides

A 4×8 bed fits 9 per sq ft of Onion. See plant counts, spacing grids, and companion pairings for every bed size →

Frequently Asked Questions

When should I plant Onion in Onaga, Kansas? +

In Onaga (Zone 6a), start Onion seeds indoors around Monday, February 23, 2026 and transplant outdoors around Monday, May 4, 2026.

What is the last frost date for Onaga, Kansas? +

The average last spring frost date for Onaga, Kansas (ZIP 66521) is around Monday, April 20, 2026. This is based on NOAA climate normals for USDA Zone 6a.

How long does Onion take to grow? +

Onion typically matures in about 100 days from transplanting. In Onaga, that means you can expect harvest around Monday, May 4, 2026 plus 100 days.

Should I start Onion indoors or direct sow in Kansas? +

Onion should be started indoors 8 weeks before your last frost date. In Onaga, that means starting around Monday, February 23, 2026.

📚 More Onion Planting Guides

🗺️

Onion in Kansas

Zone-by-zone breakdown · Full state guide

→ 🌡️

Zone 6a Onion Guide

All cities in your zone · Avg dates

→

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Growing Onion in Zone 6a

Onion (Allium cepa) is a popular garden vegetable. In Onaga, Kansas, which is in USDA Hardiness Zone 6a, you should start seeds indoors around Monday, February 23, 2026.

Your average last frost date is Monday, April 20, 2026. Plan to transplant your Onion seedlings outdoors around Monday, May 4, 2026, about 2 weeks after your last frost date.