When To Plant Onions In Southern California

If you’re a gardener in Southern California, knowing when to plant onions is your first step to a great harvest. The timing for when to plant onions in southern california is ideal thanks to our region’s mild winters, which let you grow onions through the cooler season.

Onions are a staple in the kitchen and a rewarding crop in the garden. Here, you can grow them as a fall or winter crop, unlike many colder climates. This guide gives you the simple, practical steps to get your onions started at the right time and care for them until harvest.

For most of Southern California, the prime planting window is from October through January. This schedule uses the cool months for the onions to establish roots and begin growing tops. As days lengthen in spring, the plants switch to forming bulbs.

Planting in fall allows the onions to develop a strong root system before the warmer weather arrives. This leads to larger, more robust bulbs. If you miss the fall window, you can still plant sets or transplants as late as early February in many areas.

Understanding Onion Types: Day Length is Key

Choosing the right type of onion is more important than you might think. Onions are categorized by the ammount of daylight they need to form bulbs:

Short-Day Onions: These are the best choice for Southern California. They bulb when daylight lasts 10-12 hours. Plant them in fall for a late spring harvest. Popular varieties include ‘Texas Early Grano’, ‘Granex’ (the famous Vidalia type), and ‘Red Creole’.
Intermediate-Day Onions: These need 12-14 hours of daylight. They can also work well in our region, especially if planted in late winter. Try ‘Candy’ or ‘Stockton Early Red’.
Long-Day Onions: Avoid these for our climate. They need 14-16 hours of daylight and are suited for northern states with very long summer days.

How to Plant Your Onions Step-by-Step

You can start onions from seeds, sets (small bulbs), or transplants. For a fall planting, seeds or transplants are most reliable.

Choose Your Spot: Pick a location that gets full sun—at least 6-8 hours of direct light daily. Onions won’t bulb well in shade.
Prepare the Soil: Onions need loose, well-draining soil rich in organic matter. Work in several inches of compost or aged manure. The soil pH should be between 6.0 and 7.0. Raised beds are an excellent option for ensuring good drainage.
Planting Seeds: Sow seeds ¼ inch deep and 1 inch apart. Once seedlings are a few inches tall, thin them to 4 inches apart. You can use the thinnings as green onions.
Planting Transplants/Sets: This is the easiest method. Plant them just deep enough so the base is covered, spacing them 4-6 inches apart in rows 12-18 inches apart. Don’t bury them to deep.
Water Thoroughly: Give them a good drink after planting to settle the soil around the roots.

Caring for Your Onion Crop

Consistent care through the growing season is simple but crucial.

Watering and Feeding

Onions have shallow roots, so they need consistent moisture. Water deeply when the top inch of soil feels dry, but avoid soggy soil which causes rot. Reduce watering as the bulbs mature and the tops begin to yellow and fall over.

Fertilize them lightly but regularly. Use a balanced fertilizer or one slightly higher in nitrogen (like a 10-10-10 or 16-16-8) every 2-3 weeks until the bulbs begin to swell. Then, stop fertilizing.

Weeding and Mulching

Weeds compete heavily with onions. Keep the area meticulously weeded, but be careful not to disturb the shallow onion roots. A layer of straw or light mulch can supress weeds and help retain soil moisture.

Pests and Problems

Luckily, onions have few major pests in our area. Keep an eye out for thrips, which are tiny insects that cause silvery streaks on leaves. A strong spray of water or insecticidal soap can manage them. The main disease to prevent is rot, which is avoided by ensuring your soil drains well and not overwatering.

Harvesting and Curing for Storage

Knowing when and how to harvest makes all the difference for storage life.

Green Onions: You can harvest these at any stage, as soon as the tops are tall enough to use.
Bulb Onions: Wait for the signal. When most of the tops have turned yellow, brown, and fallen over naturally, it’s time. Gently lift the bulbs from the soil with a fork.

Now, curing is essential. This process dries the outer layers to form a protective skin.

Lay the bulbs (with tops still attached) in a single layer in a warm, dry, airy place out of direct sun. A shaded patio or garage works perfectly.
Let them cure for about 2-3 weeks until the necks are tight and dry and the outer skins are papery.
Once cured, trim the roots and cut the tops down to about 1 inch. Store them in a cool, dry, dark place in mesh bags or a single layer.

Common Mistakes to Avoid

Even experienced gardeners can make a few slip-ups with onions.

Planting the Wrong Type: Choosing long-day varieties will result in small or no bulbs here.
Planting Too Deep: This can restrict bulb formation. Just cover the base.
Inconsistent Watering: Letting the soil dry out completely then flooding it can cause split or double bulbs.
Harvesting Too Early: If you pull them before the tops have fallen over, they won’t be fully mature and won’t store well.
Skipping the Cure: Onions that aren’t properly cured will rot quickly in storage.

FAQ: Growing Onions in Southern California

Can I grow onions from grocery store scraps?
You can regrow the green tops from a scallion or onion bottom in water for fresh greens, but this won’t produce a new bulb. For full bulbs, you need to start with seeds, sets, or transplants.

What if my onions flower (bolt)?
If an onion sends up a flower stalk, it has bolted. This is often triggered by a sudden cold snap or temperature fluctuation. The bulb won’t grow larger and won’t store well, so use that onion soon. Bolting is more common with plants started from sets.

How long do onions take to grow?
From planting to harvest, bulbing onions typically take 5 to 6 months in our climate. Green onions can be ready in just 8-10 weeks.

Can I grow onions in containers?
Absolutely. Choose a pot at least 10-12 inches deep with good drainage holes. Use a quality potting mix and maintain consistent watering, as containers dry out faster.

What are good companion plants for onions?
Onions are great companions for many garden vegetables. They can help deter pests from carrots, lettuce, and tomatoes. Avoid planting them too close to peas or beans, as they can sometimes inhibit eachothers growth.

By following these simple guidelines, you can enjoy a succesful harvest of sweet or pungent onions from your own garden. The mild winters here provide a perfect opportunity to grow this essential kitchen crop with ease. Just remember the golden rules: plant short-day varieties in the fall, give them sun and consistent water, and be patient for the harvest.