When to Plant Onions in Killeen, TX
Published: April 21, 2026
Onion Planting Dates for Killeen, TX
| Start seeds indoors | November 23–30 |
| Last frost (average) | February 1 |
| Transplant outdoors | January 4–14 |
| Direct sow outdoors | January 4–14 |
| Minimum soil temperature | 35°F |
| Expect first harvest | April 4 – May 4 |
| First fall frost (average) | December 15 |
⚠ CRITICAL: Choose variety based on your latitude. Short-day varieties for south of 35°N (Texas, Florida, California). Long-day varieties for north of 35°N (Ohio, Minnesota, New York). Intermediate varieties work in the middle band.
Best Onion Varieties for Killeen, TX
For Zone 8b Killeen, the best-performing onion varieties are Texas 1015, Granex, and Yellow Bermuda — all short-day varieties that bulb correctly at the shorter daylight hours south of 35°N latitude. These varieties are typically stocked by local nurseries and are the safest bets for gardeners new to onion in Killeen.
Growing Onions in Killeen
Killeen sits in Zone 8b, with an average last frost of February 1 and first fall frost around December 15 — giving a 317-day frost-free growing season. Cool-season crops like onion benefit from Killeen's cooler spring and fall windows, when temperatures stay in the 55–75°F sweet spot that produces the best flavor and least bolting.
In Killeen's warm climate, onion works best as a fall, winter, and early-spring crop. Summer heat bolts most cool-season vegetables before they can produce a harvestable head or root. Plan primary plantings in October through February in Killeen, not April through June.
Killeen's heavy clay soil benefits from raised beds or deep organic matter amendment before planting onion. Clay retains moisture well but compacts easily — add 3 to 4 inches of compost and work it in to 12 inches before planting. Consistent watering (1 inches per week) is especially important in clay soil, which can crack and pull away from roots during dry spells; mulch around plants to stabilize moisture.
Onion Calendar for Killeen
| Month | Task |
|---|---|
| November | Start seeds indoors under grow lights |
| February | Last frost — harden off seedlings outdoors |
| January | Transplant outdoors into warm soil |
| April | Expect first harvest window to open |
| December | First fall frost — harvest remaining, end of outdoor season |
Onion Tips for Killeen Gardeners
- •Match variety to latitude: short-day south of 35°N, long-day north of 35°N, intermediate in between.
- •Growing from sets (small bulbs) is fastest; growing from transplants gives the most variety options.
- •Plant cool-season onion in Killeen during October through February — spring plantings bolt before producing a usable crop in warm zones.
Common Onion Pests in Killeen
- •Onion Thrips — peaks June–August in Zone 8b (active March–October); tiny insects causing silver streaks; strong water spray removes most.
- •Onion Maggot — peaks June–August in Zone 8b (active March–October); larvae feed on bulbs; crop rotation and row covers are best defense.
- •Downy Mildew — peaks June–August in Zone 8b (active March–October); yellow patches on leaves with fuzzy underside growth; improve airflow and apply copper.
Check plants every 2–3 days during peak season — early intervention prevents most infestations from becoming serious.
What to Plant with Onions in Killeen
In Killeen's warm climate, Carrot and Tomato are the most beneficial plants to grow alongside onion. Carrot shares root-zone space without competing because carrot roots run deeper than most companions. Keep onion away from Bean — it inhibits garlic and onion bulb sizing when planted too close. Warm-climate gardeners especially benefit from dense, layered companion plantings that shade soil and reduce water loss.
Frequently Asked Questions
When should I plant onion in Killeen, TX?
In Killeen (Zone 8b), start onion seeds indoors around November 23–30 and transplant outdoors around January 4–14. The city's average last frost of February 1 is the anchor date — count 10 weeks back for seed starting and 4 weeks back for transplanting.
What zone is Killeen, TX for onion growing?
Killeen is USDA Zone 8b. For onion, this means a frost-free growing season of roughly 45 weeks running from February 1 to December 15. Cool-season crops like onion thrive in this zone with both spring and fall planting windows available.
When is onion harvest season in Killeen?
Expect the first onion harvest in Killeen around April 4, with harvest continuing through May 4. This is based on 90–120 days from transplant or direct sow.
How long does it take to grow onion in Killeen, TX?
From transplant or direct sow to first harvest, onion takes 90–120 days in Killeen's climate. Based on a typical planting date of January 4–14, expect your first harvest around April 4. Killeen's warm Zone 8b climate tends toward the faster end of this range — warmer soil and longer days accelerate maturity.
What soil does onion need in Killeen?
Killeen's heavy clay soil compacts easily and drains slowly — problematic for onion which needs oxygenated roots. Build a raised bed or amend deeply with 3–4 inches of compost worked into the top 12 inches. Add gypsum if the soil is severely compacted. Consistent watering matters especially in clay because the soil can crack and pull away from roots during dry spells.