Growing onions successfully in North Texas requires understanding the region’s specific climate and soil conditions. Due to mild winters and intense summer heat, precise timing is necessary for a successful harvest. Onions are cool-season crops that need a long growing period to develop leaves before summer heat triggers bulbing. Achieving large bulbs requires careful consideration of variety selection and planting window.
Selecting the Ideal Onion Variety for North Texas
The formation of an onion bulb is controlled by photoperiodism, the plant’s response to daylight hours. North Texas latitude requires varieties that bulb under fewer hours of light compared to northern regions. Selecting the wrong type is the most common reason for a failed crop, often resulting in only green tops instead of a bulb.
Gardeners should focus on Short-Day and Intermediate-Day varieties. Short-Day onions begin to form bulbs when day length reaches 10 to 12 hours, suiting the southern growing cycle. Examples include the Texas Super Sweet 1015Y, Yellow Granex, and Texas Early White.
Intermediate-Day types, sometimes called Day-Neutral, also perform well, bulbing when daylight reaches 12 to 14 hours. Conversely, Long-Day varieties, such as Walla Walla or Ailsa Craig, require 14 to 16 hours of daylight to bulb and will not produce a harvest at this latitude.
Optimal Planting Windows
The timing of planting is the most important factor for maximizing bulb size. Onions must establish large leafy growth during cooler months, as each leaf contributes a ring to the final bulb. Larger top growth before bulbing results in a larger harvested onion.
The primary window for planting transplants or “sets” is late January through mid-February. This places young plants in the ground four to six weeks before the average last spring freeze. Planting during this period allows the onion to develop substantial roots and foliage before increasing daylight signals bulbing.
While planting sets in late fall (October/November) is sometimes done, the late January to mid-February window is recommended for transplants for the main harvest. Those starting onions from seed should aim for a mid-to-late October planting. This earlier fall planting allows seeds time to sprout and overwinter before resuming growth in spring.
Preparing the Planting Site
Onions are shallow-rooted and require loose, well-drained soil to allow the bulb to expand. North Texas soils often contain heavy clay, which can compact and inhibit growth. Incorporating organic material, such as compost or well-rotted manure, improves aeration and drainage in in-ground beds.
For areas with heavy clay, using raised beds is often the most effective solution. Raised beds allow for an optimal growing medium, often a 50/50 blend of topsoil and compost. The planting site should receive full sun, meaning at least eight hours of direct sunlight daily.
Onions perform best in slightly acidic to neutral soil, with a target pH range between 6.0 and 7.0. Before planting, amend the soil with a fertilizer higher in phosphorus. Phosphorus encourages strong root development, which supports the plant’s ability to produce a large bulb.
Care and Maintenance Through Harvest
Consistent care after planting supports the leaf growth required for large bulbs. Onions have a high demand for moisture due to shallow roots and should receive about one inch of water per week. Water slowly and deeply to encourage root growth without keeping the soil soggy, which can lead to rot.
Weeding is continuous because onions do not compete well with surrounding plants for nutrients and moisture. Shallow cultivation or hand-pulling is recommended to remove weeds, as deep hoeing can damage the shallow roots. Applying mulch or compost helps suppress weeds and maintain soil moisture.
Once plants are actively growing in spring (around five to six leaves), they require regular feeding with a nitrogen-heavy fertilizer. Nitrogen fuels foliage growth, and side-dressing with a high-nitrogen product every two to three weeks is recommended until bulbing begins. Stop nitrogen application when the neck softens and the bulb starts to swell, usually around mid-April, to ensure proper development and curing.
Harvesting typically occurs in late spring or early summer, approximately 100 to 115 days after planting. The plant signals maturity when the tops naturally weaken and fall over, indicating the bulb is finished growing. After this “top flop,” pull the onions and allow them to cure in a warm, dry, well-ventilated area for several weeks to dry the outer skins and neck for long-term storage.