Growing Onions on Marion County

By Rick Tenison
Marion County Master Gardeners

Why Onion Type Matters
Onions form bulbs based on day length, not temperature. Choosing the correct type is the single most important factor for success.

​Short-Day Onions

• Start bulbing at 10–12 hours of daylight
• Best for the South and lower Midwest
• Produce bulbs earlier in the season
• Excellent choice for Marion County

Intermediate-Day Onions

• Start bulbing at 12–14 hours of daylight
• Work well in the middle of the country​
• Slightly later harvest than short-day
• ​Also a good option for Marion County

​Long-Day Onions

• Require 14–16 hours of daylight
• Best for northern states
• In Arkansas, they often fail to bulb properly
• Not recommended here

Bottom line:
👉 Short-day and intermediate-day onions work best in Marion County, AR because our day length triggers bulbing at the right time, before heat stress sets in.

When to Plant

• Plant onion plants, not seeds, for best results
• Ideal planting window: late January through February
• Onions tolerate light frost and prefer cool early growth

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Soil & Bed Preparation

• Loose, well-drained soil is critical
• Raised beds work exceptionally well
• Target soil pH: 6.0–6.8
• Mix in compost, but avoid fresh manure

Spacing

• 4–6 inches apart for medium to large bulbs
• Rows 12–18 inches apart
• Plant shallow: roots covered, bulb top at soil surface

Fertilization Basics
Onions are heavy feeders, especially nitrogen early on.

Early Growth (first 6–8 weeks):

• Use a high-nitrogen fertilizer
• Feed every 2–3 weeks
• Strong leaf growth = larger bulbs later

Bulb Formation:

• Reduce nitrogen once bulbing starts
• Stop fertilizing when bulbs begin swelling
• ⚠️ Too much nitrogen late in the season leads to poor storage quality.

Watering

• Consistent moisture is key
• About 1 inch of water per week
• Avoid water stress during bulbing
• Reduce watering as tops fall over before harvest

Harvest & Curing

• Harvest when tops fall over naturally
• Pull bulbs and cure in a warm, dry, well-ventilated area
• Cure for 2–3 weeks
• Trim tops and roots after curing

Storage Tips

• Store only fully cured onions
  
• Cool, dry location with good airflow
  
• Short-day onions generally store a few months
  
• Intermediate-day onions store longer
  
• 90% of the yellow onions sold in grocery stores are ‘Yellow Globe’ or ‘Spanish’ onions (Patterson or Copra), also known as storage onions, primarily long-day onions.
  
• White Sweet Spanish is the common white onion.
  
• Red Wing and Red Baron are common commercial red onions.
  
• “Sweet Onions” do not store well - Vidalia, Walla Walla, Texas Super Sweet. We recommend freezing for long-term storage.
  

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