The warm, extended growing season along the Gulf Coast offers unique gardening opportunities, but success with crops like onions requires precise local knowledge. In Houston, Texas, mild winters and early springs necessitate a different planting timetable than in northern climates. Achieving large, sweet bulbs depends on selecting the right variety and planting when it aligns with the region’s specific daylight patterns and temperature fluctuations.
Ideal Planting Windows for Houston Onions
Onions are a cool-season crop requiring a long, uninterrupted period of vegetative growth before bulbing begins. The ideal planting time in Houston is late fall through early winter, allowing for robust root and foliage development during the mildest months. Direct seeding should occur between October and December.
If using transplants (small, pencil-thin seedlings), the planting window shifts to January and February. Planting transplants during this late winter period bypasses the risk of the plants “bolting,” or prematurely sending up a flower stalk. Bolting can occur if they experience an early warm spell followed by a hard freeze. This cool-weather establishment ensures the plant has sufficient green growth before lengthening days trigger the bulb formation process.
Selecting Short-Day Onion Varieties
The most important decision for a Houston gardener is selecting an onion variety adapted to the southern latitude. Onions are photoperiod-sensitive, relying on a specific number of daylight hours to signal the shift from producing leaves to forming a bulb. Traditional “long-day” varieties, common in northern states, require 14 to 16 hours of daylight, which Houston does not reach early enough for proper bulbing.
Gardeners in the Gulf Coast region must choose “short-day” varieties, which begin to bulb when daylight reaches approximately 10 to 12 hours. This adaptation ensures the bulb develops fully before the intense heat of summer arrives. Recommended varieties for this climate include:
- Texas 1015 SuperSweet
- Yellow Granex (the type used for Vidalia onions)
- Texas Legend
- Southern Belle Red
The Texas 1015Y is a yellow, globe-shaped onion specifically bred for reliable performance in this southern environment.
Preparing the Soil and Planting Techniques
Onions are shallow-rooted and require loose, well-drained soil for easy bulb expansion. Before planting, work the soil 8 to 10 inches deep and amend it with compost or aged manure to improve aeration and drainage. The preferred soil pH range is slightly acidic, ideally between 6.2 and 6.8.
When planting transplants, place them shallowly, no deeper than one inch, with the roots covered and the bulb’s shoulder near the soil surface. Planting too deeply inhibits the bulb’s ability to swell and form properly. Space transplants four to six inches apart to allow each plant room to develop a full-sized bulb.
Gently press transplants into the prepared soil, ensuring the delicate roots point downward. Some gardeners use a pencil or small dowel to create the shallow planting hole before inserting the plant. After planting, incorporate a starter fertilizer higher in phosphorus, such as a 10-20-10 blend, into the top few inches of the soil to encourage early root growth.
Essential Care and Harvesting
Consistent moisture is necessary for developing large, juicy bulbs due to the onion’s shallow root system. Watering once a week is a general guideline during the spring, but adjust this frequency for dry or windy weather. Allow the soil to dry out slightly between waterings to prevent rot and fungal issues.
Onions are heavy feeders, requiring regular fertilization throughout their vegetative growth period. Follow an initial application of all-purpose fertilizer with a high-nitrogen feed, such as ammonium sulfate, every two to three weeks until bulbing begins. Once bulbing starts, switch to a fertilizer lower in nitrogen to support bulb development rather than leaf growth. Keep the planting area free of weeds, which compete directly for water and nutrients.
The final stage of the growing cycle is signaled when the onion tops begin to turn yellow and fall over naturally. This bending indicates the plant has stopped transferring energy to the foliage and is redirecting it into the bulb for final maturation. Cease watering at this point to allow the soil to dry out before harvesting. Pull mature bulbs from the ground on a sunny day and leave them to dry, or cure, in the garden for one or two days before moving them to a dry, ventilated location for further curing.