Planting Guides

When to Plant Onions in Houston: Complete Guide + Best Varieties for Zone 9a

Houston, Texas

USDA Zone 9a

Last Frost: Feb 15

Last updated: October 30, 2025

Plant onions in Houston October-December for spring harvest. Zone 9a requires short-day varieties like Texas Super Sweet for proper bulbing.

AAisha Patel

October 30, 2025

Short-day onion transplants being planted in Houston garden in November for spring harvest — — Image © PlantReference.org 2026

Quick Answer

Plant short-day onions in Houston October through December. Harvest March through May when fall-planted transplants mature in 120-140 days.

TL;DR

Plant short-day onions in Houston October through December for best results. Zone 9a requires varieties like Allium cepa 'Texas Super Sweet' that bulb in 10-12 hours of daylight. Transplants work best, planted 4 inches apart in well-drained soil. Harvest occurs March through May when planted at optimal fall timing.

Frequently Asked Questions

Can I plant long-day onion varieties in Houston?

No, long-day varieties will never bulb in Houston's climate. Our latitude of 30°N means summer days only reach 13.5 hours maximum, while long-day onions need 14-16 hours of daylight to trigger bulbing. Plant these varieties and you'll get giant green tops but no bulbs—essentially expensive scallions. Stick to short-day varieties like Allium cepa 'Texas Super Sweet' that bulb in 10-12 hours for guaranteed success.

When is too late to plant onions in Houston?

The absolute latest safe planting date is February 14—our average last frost date. However, planting after January 15 significantly reduces bulb size because onions need 100+ days of vegetative growth before day length triggers bulbing in March. October through November planting produces the largest bulbs, while December through January planting still works but yields smaller onions.

Why are my Houston-grown onions so small?

Small bulbs usually indicate planting too late in the season or choosing the wrong variety type. Short-day onions need maximum growing time before March day-length triggers bulbing. Late plantings (after January) don't develop sufficient leaf area to support large bulb formation. Also verify you're using true short-day varieties—intermediate or long-day types produce small bulbs in Houston regardless of planting timing.

Do I need to protect onions from Houston's occasional freezes?

Most short-day onion varieties tolerate Houston's brief winter freezes without protection. However, newly planted transplants benefit from row covers during hard freezes (below 28°F for more than 4 hours). Established plants (30+ days in ground) are quite cold-hardy. The bigger risk is soil becoming waterlogged after freeze-thaw cycles in our clay soils.

Can I grow onions from seed in Houston?

Yes, but direct seeding in Houston requires precise timing. Start seeds indoors October 1-15 for transplanting in late November, or direct seed in prepared beds October 15-November 1. Seeds need 70-75°F soil temperatures for germination, which can be challenging during our variable fall weather. Transplants offer better success rates for most Houston gardeners, especially beginners.

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Tagged with

#houston gardening #zone 9a planting #short day onions #texas onions #fall planting #onion varieties #houston climate #texas gardening #southern onions #gulf coast gardening

Written By

Aisha Patel

Aisha manages a small tropical nursery on the east side of Houston, specializing in plants that can handle the Gulf Coast's humidity, heat, and unpredictable flooding. She studied horticulture in college and worked at a wholesale grower before opening her own operation. Growing up, her parents kept a kitchen garden with okra, bitter gourd, and curry leaf plants—a tradition she's continued. Houston's subtropical climate lets her grow things most of the country can't, but it also means dealing with fungal issues, standing water, and summers where it's too hot for even tomatoes. Aisha writes about tropical and subtropical plant care, humidity management, and working with heavy clay soils.