Growing onions in Texas presents a unique challenge due to the state’s wide range of climates, which makes precise planting time essential for a successful harvest. Onions are cool-season crops that thrive during the mild Texas winter and spring. The difference between a large, sweet bulb and a disappointing green stem often comes down to timing the planting to align with the plant’s specific light requirements. This careful scheduling ensures the plants have enough time to develop sufficient foliage before the summer heat and the lengthening daylight hours trigger the final stage of bulb formation. The goal is always to maximize vegetative growth before bulbing begins.
Day Length Requirements for Texas Onions
Onion bulb development is controlled by a phenomenon called photoperiodism, which means the plant requires a specific duration of daylight hours to begin forming a bulb. Onions are broadly classified into three types based on this light sensitivity: Short-Day, Intermediate-Day, and Long-Day varieties. Short-Day onions, which are the primary type grown across most of Texas, begin to bulb when the daylight reaches 10 to 12 hours.
Intermediate-Day varieties need a slightly longer exposure, starting to bulb when daylight hits 12 to 14 hours. Because Texas sits at a lower latitude, the longest summer day length is insufficient for Long-Day onions, which require 14 to 16 hours of light to bulb properly. Gardeners in the southern and central parts of the state must select Short-Day varieties, like the ‘Texas SuperSweet 1015.’ Those in the northern regions may successfully grow Intermediate-Day types. Planting the wrong type will result in the onion remaining a green stalk or forming a very small, undeveloped bulb.
Regional Planting Schedules Across Texas
The most suitable time to plant onion transplants in Texas varies significantly depending on the region, aligning with the local climate and the need for a cool growing season. Across all regions, the goal is to plant in the fall or winter so the bulbs can be harvested from May to July.
South Texas
In South Texas, including the Rio Grande Valley, the earliest planting window opens in the fall. Transplants can be set out as early as late September through October to take advantage of the mild winter. This early planting allows for maximum vegetative growth before the onset of bulbing in the spring.
Central Texas
In Central Texas, in areas like Austin and San Antonio, the primary window for planting onion transplants is generally between December and January. Starting from seed must occur earlier, typically mid-October, to give the seedlings enough time to mature before the bulbing stage. Planting transplants during this winter period is a common practice.
North Texas
For gardeners in North Texas, including the Dallas-Fort Worth and Panhandle areas, the planting schedule shifts later due to colder winter temperatures. The ideal time to plant onion transplants is late January through mid-February. Planting too early risks the plants bolting—prematurely sending up a flower stalk—if exposed to a late winter cold snap.
Choosing Planting Material: Seeds Versus Transplants
Onions can be started from seeds, sets, or transplants, with the choice influencing the required planting time and overall success rate. Starting from seed is the most economical option and offers the widest selection of varieties, but it requires a much earlier start, often indoors or in the garden in October. Seeds take longer to mature, increasing the risk of early die-off, and require careful thinning once the seedlings are established.
Transplants, which are young onion plants that look like thick scallions, are the preferred method for most Texas gardeners. They provide a six-week head start over seeds, leading to faster maturity and a higher success rate. Transplants are less prone to bolting than onion sets—small, dried bulbs that often have limited variety selection.
Post-Planting Care and Anticipating Harvest
Once the transplants are in the ground, consistent care is necessary to ensure the development of large, healthy bulbs. Onions are heavy feeders and require a consistent supply of nitrogen to maximize leaf growth, as each leaf corresponds to a ring in the final bulb. A high-nitrogen fertilizer should be applied every two to four weeks after planting.
This fertilization should stop once the plant begins the bulbing process, which is often visible when the soil around the bulb starts to crack. Consistent and deep watering is also important throughout the growing season, especially during dry, windy weather, to keep the soil evenly moist but not waterlogged. The final stage of the onion cycle, and the signal for harvest, occurs when the tops begin to yellow and fall over. The bulbs are ready for harvest when about one-third of the tops have collapsed at the neck, which typically happens in late spring to early summer. After pulling the onions, they should be left to dry in the field for a few days to cure before being stored.