Short Day Onion Plants: Complete Growing Guide

Short day onion plants require 10-12 hours of daylight to form bulbs, making them ideal for southern U.S. regions below 32° latitude. Plant them in fall for spring harvest to enjoy sweet, flavorful onions perfect for fresh eating.

Why Short Day Onions Thrive in Southern Climates

Short day onion plants (Allium cepa) begin bulb formation when daylight reaches 10-12 hours—a critical adaptation for southern growing regions. Unlike long day varieties that need 14+ hours of light, short day onions respond to the shorter days of fall and early spring, making them the only practical choice for gardeners in USDA zones 7 and south.

According to the Texas A&M AgriLife Extension, short day onions produce larger bulbs with higher sugar content in southern climates, yielding that distinctive sweet flavor prized by chefs. Their growth cycle aligns perfectly with the mild winter temperatures of the Deep South, where they establish roots during cool months and mature as days lengthen in spring.

Onion Type	Daylight Requirement	Best Growing Regions	Planting Season	Flavor Profile
Short Day	10-12 hours	Southern US (below 32° latitude)	Fall planting	Sweet, mild
Intermediate Day	12-14 hours	Mid-latitudes (32°-36°)	Late winter/early spring	Moderately sweet
Long Day	14+ hours	Northern US (above 36° latitude)	Early spring	Stronger, pungent

Your Seasonal Roadmap for Short Day Onion Success

Timing is everything with short day onion plants. Plant too early and they'll bolt in summer heat; too late and they won't develop properly before spring temperatures rise. The University of Florida's Institute of Food and Agricultural Sciences confirms that precise planting windows maximize yield and quality.

Here's your step-by-step planting timeline for southern regions:

• September-October: Prepare soil with 3-4 inches of compost; aim for pH 6.0-6.8
• October-November: Plant sets or transplants 1 inch deep, 4-6 inches apart
• December-January: Apply balanced fertilizer when plants reach 6 inches tall
• February-March: Reduce watering as bulbs begin to swell
• April-May: Harvest when tops fall over naturally

Top Short Day Varieties for Southern Gardens

Not all short day onions perform equally across southern regions. Based on multi-year trials by the University of California Cooperative Extension, these varieties consistently deliver:

• Texas Early Grano: The classic sweet onion with excellent storage (4-6 months)
• Granex: Parent of Vidalia onions; exceptionally sweet with golden skin
• 1015Y: Named for October 15 planting date; mild flavor perfect for salads
• Red Creole: Deep purple skin with sharp flavor that mellows when cooked

For best results, purchase disease-resistant varieties certified by your state's agricultural extension. Avoid supermarket onions for planting—they're often treated to prevent sprouting and may carry diseases.

Avoid These Common Short Day Onion Mistakes

Even experienced gardeners struggle with short day onions when they overlook these critical factors:

Soil Preparation Oversights

Short day onions need loose, well-drained soil. Compacted soil leads to misshapen bulbs. Incorporate 3-4 inches of compost and avoid nitrogen-heavy fertilizers before planting, which encourage excessive top growth at the expense of bulb development.

Watering Inconsistencies

These onions require consistent moisture during establishment but need reduced watering as bulbs mature. The USDA Agricultural Research Service found that alternating dry/wet periods causes onion doubling (multiple bulbs) and increases disease susceptibility. Maintain even soil moisture until the final 3 weeks before harvest.

Ignoring Regional Adaptation

Not all short day varieties perform equally across southern regions. Coastal areas need varieties resistant to pink root disease, while inland regions require heat-tolerant types. Consult your local extension office for region-specific recommendations—this simple step can increase your yield by 30% according to Mississippi State University trials.

Harvesting and Storage Secrets

Knowing when to harvest short day onions makes all the difference between sweet perfection and bitter disappointment. Watch for these visual cues:

• Top leaves begin to yellow and fall over naturally
• Neck of the plant becomes soft and begins to collapse
• Bulb wrappers turn dry and papery

After harvesting, cure onions in a warm, dry, well-ventilated area for 2-3 weeks. Properly cured short day onions store for 3-4 months at 32-35°F with 65-70% humidity. Don't refrigerate—cold temperatures convert sugars to starches, ruining their signature sweetness.

Troubleshooting Guide: Quick Fixes for Common Problems

Problem	Most Likely Cause	Solution
Small bulbs	Planted too late, overcrowded, or excessive nitrogen	Plant earlier, thin to 4-6" spacing, use balanced fertilizer
Bolting (flowering)	Exposure to cold spells after planting	Remove flower stalks immediately; harvest early
Soft, rotting bulbs	Overwatering during bulb maturation	Reduce watering 3 weeks before harvest
Pale, weak plants	Nutrient deficiency or poor soil preparation	Apply balanced fertilizer; amend soil with compost

When should I plant short day onion plants in Texas?

Plant short day onion sets or transplants in Texas from October through November. This timing allows roots to establish during cool weather while preventing premature bulb formation. Planting too early risks bolting from summer heat; too late reduces bulb size. Central Texas gardeners should target mid-October planting, while South Texas can wait until early November.

Can I grow short day onions in containers?

Yes, you can successfully grow short day onions in containers with proper care. Use pots at least 12 inches deep with excellent drainage. Fill with high-quality potting mix amended with compost. Plant sets 1 inch deep, spacing 4 inches apart. Container-grown onions need more frequent watering and weekly applications of balanced liquid fertilizer. Expect smaller bulbs than garden-grown plants, but flavor remains excellent.

Why are my short day onions pungent instead of sweet?

Short day onions become pungent when harvested too early or grown in stressful conditions. They need sufficient time to develop sugars—typically 100-110 days from planting. Excessive nitrogen fertilizer, inconsistent watering, or harvesting before tops naturally fall over all contribute to sharp flavor. For maximum sweetness, allow plants to mature fully and cure properly before storage.

How do I prevent onion maggots in my short day onion patch?

Prevent onion maggots by rotating crops annually and using floating row covers from planting through early spring. Apply beneficial nematodes to the soil in fall to target overwintering larvae. If infestation occurs, remove and destroy affected plants immediately. The University of Georgia recommends planting resistant varieties like 'Texas Early Grano' and avoiding planting near previous allium crops.