When To Plant Onions In South Texas

If you’re planning your garden in South Texas, knowing when to plant onions is the first step to a great harvest. Getting the timing right is crucial for growing big, flavorful bulbs in our unique climate.

Onions are a cool-season crop, which means they prefer to grow during the milder parts of the year. In South Texas, our winters are relatively short and mild, and our summers are long and hot. This gives us a specific planting window that’s different from northern states. Planting at the correct time allows the onions to establish roots and leaves before the heat triggers bulb formation. If you plant too late, the plants won’t have enough time to grow large before the summer heat causes them to go dormant or bolt (send up a flower stalk).

For most of South Texas, the optimal time to plant onion sets, transplants, or seeds is in the fall. The goal is to get them in the ground so they can grow through the cool winter and be ready to form bulbs as the days lengthen in spring.

Here’s a simple seasonal guide:

Fall Planting (Best Method): Plant between mid-October and late November. This is the most common and successful timeframe.
Winter Planting: If you miss the fall window, you can plant up until late January in most areas, but the harvest may be smaller.
Spring Planting: Generally not recommended. Onions planted in spring often struggle with the rapidly warming soil and may bolt quickly.

Your specific location within South Texas can shift these dates slightly. Gardeners in the Rio Grande Valley might plant a bit later in November, while those in the San Antonio area might aim for earlier in October. A good rule is to get them in the ground about 4-6 weeks before the first expected frost date, which allows for good root development.

Understanding Onion Types: Short-Day vs. Long-Day

This is the most important factor for success in the South. Onions form bulbs based on day length (the number of sunlight hours).

Short-Day Onions: These are the ones you must plant in South Texas. They begin forming bulbs when daylight lasts 10-12 hours, which matches our spring perfectly. Popular varieties include Texas Super Sweet, Texas Early White, 1015Y, and Red Creole.
Long-Day Onions: These need 14-16 hours of daylight to bulb, which we don’t get. They will never form good bulbs here, so avoid them.

Always check the seed packet or plant tag to ensure you’re buying short-day varieties. It’s the non-negotiable key to a good crop.

Choosing Your Planting Method

You have three options for starting your onions, each with its own pros and cons.

1. Onion Sets (Small Bulbs)

These are the easiest for beginners. Sets are small, dormant onion bulbs from the previous year. You simply plant them in the ground. They establish quickly but have a slightly higher chance of bolting and offer less variety choice. Plant them about 1 inch deep and 4 inches apart.

2. Onion Transplants (Seedlings)

These are young plants, often sold in bunches at local nurseries in the fall. They are an excellent choice for South Texas because they give the onions a head start. You get a wider variety than with sets and a very reliable harvest. Gently separate the seedlings and plant them about 1 inch deep, spacing them 4-6 inches apart.

3. Onion Seeds

Starting from seed offers the widest variety and is the most economical, but it requires the most time and planning. In South Texas, you would sow seeds directly in the garden in October. They need consistent moisture to germinate. Thin the seedlings to the proper spacing once they are a few inches tall.

Step-by-Step Planting Guide

Choose the Right Spot: Select a location that gets full sun—at least 6-8 hours of direct sunlight daily.
Prepare the Soil: Onions need loose, well-draining soil rich in organic matter. Work in several inches of compost or well-rotted manure. Raised beds are ideal for ensuring good drainage, which is critical to prevent rot.
Check Soil pH: Onions prefer a slightly acidic to neutral pH, between 6.0 and 7.0. A simple soil test can tell you if you need to adjust it.
Plant Correctly: Plant sets or transplants about 1 inch deep. Space them 4 inches apart in rows that are 12-18 inches apart. If planting from seed, sow thinly and thin later.
Water Thoroughly: Water immediately after planting to settle the soil around the roots or seeds.

Caring for Your Onion Crop

Consistent care through the winter and spring leads to the best bulbs.

Watering: Onions have shallow roots, so they need consistent moisture. Water deeply when the top inch of soil feels dry. Reduce watering as the bulbs mature and the tops begin to yellow and fall over.
Weeding: Keep the area weed-free. Weeds compete heavily for nutrients and water. Hand-pull weeds carefully to avoid disturbing the onion’s shallow roots.
Fertilizing: Use a balanced fertilizer or one slightly higher in nitrogen at planting. Side-dress with a nitrogen fertilizer every 4-6 weeks until the bulbs begin to form. Stop fertilizing once the bulbs start to swell.
Mulching: Apply a light layer of straw or grass clippings to help retain soil moisture, suppress weeds, and moderate soil temperature.

Common Problems and Solutions in South Texas

Our climate brings specific challenges. Here’s how to handle them:

Bolting: This is when an onion sends up a flower stalk. The bulb stops growing and becomes tough. It’s often caused by temperature fluctuations or planting the wrong type. To prevent it, plant at the right time, use short-day varieties, and choose bolt-resistant transplants. If one bolts, harvest and use it right away.
Pests: Thrips are tiny insects that can silver the leaves. Use a strong spray of water or insecticidal soap to control them. Onion maggots are less common but can be deterred with crop rotation.
Diseases: Fungal diseases like downy mildew or pink root can occur, especially in wet conditions. The best defense is well-draining soil, proper spacing for air flow, and avoiding overhead watering.

Harvesting and Storing Your Onions

Your onions will tell you when they’re ready. In late spring or early summer, the tops will turn yellow and begin to fall over naturally.

Stop Watering: Once most tops have fallen, stop watering to allow the bulbs to cure.
Harvest: On a dry day, gently lift the bulbs from the soil with a fork.
Cure: Lay them in a single layer in a warm, dry, well-ventilated place out of direct sun for about 2-3 weeks. This allows the outer skins to dry and tighten for storage.
Store: After curing, trim the roots and cut the tops down to about 1 inch. Store in a cool, dry, dark place in mesh bags or a single layer. Properly cured short-day onions don’t store as long as some types, but you can still enjoy them for several months.

FAQ: Planting Onions in South Texas

What is the best month to plant onions in South Texas?
The best month is typically November. Mid-October through late November is the ideal range for fall planting.

Can I plant onions in February in Texas?
In South Texas, you can plant transplants in early February at the latest, but it’s not ideal. The later you plant, the smaller your bulbs will be because they have less time to grow before bulbing begins.

Is it better to grow onions from seeds or sets?
For beginners, sets or transplants are easier and more reliable. For experienced gardeners wanting specific varieties, seeds are great. Transplants offer a good balance of choice and ease.

Why are my onions not forming bulbs?
The most common reasons are: 1) You planted a long-day variety instead of a short-day variety. 2) You planted to late in the season. 3) The plants were overcrowded or lacked enough nutrients and water during leaf growth.

How often should I water onion plants?
Water deeply about once a week, depending on rainfall. The key is consistent moisture, not soggy soil. Always check the soil first.

By following this guide and paying attention to the short-day requirement and fall planting window, you’ll be well on your way to a succesful onion harvest. There’s nothing quite like pulling your own sweet, homegrown onions from the garden.