If you want a successful onion crop in Houston’s unique climate, knowing exactly when to plant onions is the most important step. For optimal harvest timing, you need to work with our long growing season and mild winters, not against them.
This guide gives you the clear, practical schedule and tips you need. We’ll cover the best planting dates, variety selection, and simple care steps to get you from sets or seeds to a hearty harvest.
When to Plant Onions in Houston – For Optimal Harvest Timing
The golden rule for Houston gardeners is to plant onions in the fall. This timing is non-negotiable for optimal results. Our winters are mild enough that onions can establish roots and begin growing before the cold, then really take off as days lengthen in spring, bulbing up before the intense summer heat arrives.
Planting in spring is possible, but it’s a race against the clock. The bulbs often don’t have enough time to size up before heat triggers them to stop growing.
Your Houston Onion Planting Calendar
Here is your straightforward seasonal schedule. Stick to these windows for the best chance of success.
* Optimal Fall Planting Window: October 15th – November 30th. This is the sweet spot. The soil is still warm from summer, which encourages root growth, but the air is cooling down.
* Late Fall / Winter Planting: Up until mid-January is acceptable, especially if using transplants (small seedlings). The later you plant, the smaller your final bulbs may be, as they have less time to grow before bulbing begins.
* Spring Planting (If Necessary): Plant by early February at the absolute latest. Use fast-maturing, short-day varieties and be prepared for a potentially smaller harvest.
Choosing the Right Onion Type for Houston
Onions are classified by how much daylight they need to form a bulb. Getting this right is critical in our southern latitude.
* Short-Day Onions: This is what you must plant in Houston. They begin forming bulbs when daylight lasts 10-12 hours. They are perfectly suited to our southern winters and springs.
* Intermediate-Day & Long-Day Onions: Avoid these for fall planting. They need 13-16 hours of daylight to bulb, which happens too late in our season, after it’s already gotten hot.
Recommended Short-Day Varieties for Houston
Choose from these proven performers. You can find them as seeds, sets (tiny bulbs), or transplants.
* Texas Legend: A mild, sweet yellow onion developed right here for Texas conditions. Excellent storage potential.
* Texas Early White: A productive, early-maturing white onion with a crisp bite.
* 1015Y SuperSweet: The famous “Texas SuperSweet” onion. It’s very sweet and mild but does not store for long—eat these first!
* Red Burgundy: A reliable red onion with beautiful color and good flavor for salads and grilling.
* Granex: The classic Vidalia-type sweet onion. Very mild and juicy.
Step-by-Step Planting Guide
Follow these steps to get your onions off to a strong start.
1. Choose Your Planting Method.
* Transplants (Best for Beginners): Small seedlings from a nursery. They establish quickly and give you a head start.
* Sets (Easiest): Small, dormant onion bulbs. Plant them pointy-end up. They are forgiving but can bolt (flower) more easily if stressed.
* Seeds (Most Economical): Start seeds indoors in September or direct sow in October. Requires the most time and care.
2. Prepare Your Soil.
Onions need loose, well-draining soil rich in organic matter. Houston’s heavy clay needs ammendment.
* Work in 3-4 inches of compost or well-rotted manure into the top 8 inches of soil.
* Ensure the planting bed is in full sun—at least 6-8 hours of direct light daily.
* A soil test is helpful; onions prefer a slightly acidic to neutral pH (6.0-7.0).
3. Plant Correctly.
* Space plants or sets 4 inches apart in rows that are 12 inches apart.
* Plant them so the base (where roots emerge) is just 1 inch deep. Don’t bury them too deeply.
* Water thoroughly after planting to settle the soil.
Caring for Your Onion Crop
Consistent care is simple but makes a huge difference in your final harvest size.
Watering and Feeding
Onions have shallow roots and need consistent moisture, but not soggy soil.
* Water deeply 1-2 times per week, depending on rainfall. The goal is about 1 inch of water per week.
* Reduce watering as the bulbs mature and the tops begin to yellow and fall over.
* Fertilize every 3-4 weeks with a nitrogen-rich fertilizer (like a 21-0-0) until bulbing begins. Stop high-nitrogen feeds once you see the soil crack as the bulb expands.
Weeding and Mulching
Weeds compete fiercely with onions for nutrients and water.
* Weed gently and regularly by hand to avoid damaging the shallow onion roots.
* Apply a 2-3 inch layer of mulch (straw, shredded leaves, or grass clippings) around the plants. This suppresses weeds, retains soil moisture, and keeps soil temperature more even.
Knowing When to Harvest
Harvest timing is just as important as planting timing. Watch for these signs:
1. The “Tops Down” Signal: In late April or May, the green onion tops will naturally turn yellow, weaken, and fall over. This is the plant’s way of saying it’s done growing.
2. Stop Watering: Once most tops have fallen, stop watering to allow the bulbs to cure and the outer skins to dry.
3. The Harvest: On a dry, sunny day, gently lift the bulbs from the soil with a garden fork. Be careful not to bruise them.
Curing and Storing Your Harvest
Proper curing is essential for onions to develop a protective papery skin and store well.
* Lay the harvested bulbs in a single layer in a warm, dry, airy place out of direct sun. A covered porch, garage, or well-ventilated shed is perfect.
* Let them cure for about two weeks, until the necks are completely tight and dry and the outer skins are papery.
* After curing, trim the roots and cut the dried tops down to about 1 inch.
* Store your cured onions in a cool, dry, dark place with good air circulation. Mesh bags, old pantyhose, or slotted crates work great. Check them occasionally and use any that show signs of softening first.
Common Problems and Solutions in Houston
* Bolting (Flowering): Caused by temperature swings or planting the wrong type. Once an onion sends up a flower stalk, the bulb stops growing. Harvest and use bolted onions immediately, as they won’t store. Choose the right short-day varieties and plant in the proper window to minimize this.
* Small Bulbs: Usually caused by late planting, overcrowding, insufficient sunlight, or inconsistent watering. Give them the space, food, and water they need from the start.
* Pests: Thrips are the main insect pest. They cause silvery streaks on leaves. Control them with a strong spray of water or insecticidal soap. Good garden hygiene helps prevent maggots.
* Diseases: Fungal issues like downy mildew can occur in our humid springs. Ensure good spacing for air flow, water at the soil level (not overhead), and rotate your onion bed each year.
FAQ: Your Houston Onion Questions Answered
Can I grow onions from grocery store scraps?
You can regrow green scallion tops in water for a short while, but you cannot grow a full new bulb from a store-bought onion bottom in our climate. It’s best to start with proper seeds, sets, or transplants.
Why are my onion tops falling over early?
If they fall over in winter or early spring, it could be due to overwatering, disease, or physical damage. The natural fall-over should happen in late spring as the bulb matures.
What’s the difference between green onions and bulb onions?
Green onions (scallions) are simply bulb onions harvested very early, before the bulb swells. You can grow any variety as a green onion by harvesting young.
Can I plant onions in containers?
Absolutely. Use a container at least 10 inches deep with good drainage holes. Plant varieties closer together (about 3 inches apart) and be extra vigilant about watering, as pots dry out faster.
How do I get sweeter onions?
Choosing a sweet variety like 1015Y is the first step. Consistent watering and using a sulfur-low soil can also help reduce pungency and increse sweetness.
Getting your timing right is the foundation. By planting your short-day onions in that crucial fall window, you give them the full season they need to produce robust, flavorful bulbs. With this schedule and care tips, you’re set for a rewarding harvest come late spring. Just remember to start with good soil, keep them weeded and watered, and be patient as they do their work underground.