If you’re gardening in Northern California, knowing when to plant onions is the key to a successful crop. For optimal harvest timing, you need to sync your planting schedule with the region’s unique coastal and inland climates.
Onions are a staple in the kitchen garden, but getting those perfect, large bulbs depends heavily on when you get them in the ground. This guide will walk you through the best dates, varieties, and methods to ensure you harvest a bounty of onions at just the right time.
When To Plant Onions In Northern California – For Optimal Harvest Timing
This core schedule is your starting point. Northern California’s climate is diverse, but we can break it down into two main zones: coastal areas (cooler, influenced by fog) and inland valleys (warmer, with more distinct seasons).
For most of the region, the prime planting window is in late fall through winter. This might seem counterintuitive, but onions grown from seed or sets need a long, cool period to establish roots and begin bulbing when days lengthen in spring.
- Coastal Areas (SF Bay Area, North Coast): Plant from October through January. The mild winters allow for steady growth without a hard freeze.
- Inland Valleys (Sacramento, San Joaquin Valley): Plant from November through early February. Avoid planting too late, or the bulbs won’t have time to size up before summer heat arrives.
- Mountainous Regions: Wait until the ground is workable in early spring, typically April or May, and use short-day varieties.
Understanding Onion “Day-Length” Types
This is the most important factor for choosing your variety. Onions bulb in response to daylight hours. Picking the wrong type for your location is a common reason for small bulbs.
- Long-Day Onions: Need 14-16 hours of daylight to bulb. Best for Northern states with long summer days. They generally do not perform well in California.
- Short-Day Onions: Bulb with 10-12 hours of daylight. Perfect for Southern states and California’s mild winters. They are planted in fall/winter and bulb in early spring.
- Intermediate-Day (Day-Neutral) Onions: Bulb with 12-14 hours of daylight. These are the best choice for most of Northern California. They offer flexibility and reliable results across our climate zones.
Choosing Your Onion Varieties
Stick with short-day and intermediate-day types. Here are some proven winners for our region:
- Yellow/Brown: ‘Stockton Early Red’, ‘Superstar’ (white), ‘Red Burgundy’
- White: ‘White Granex’ (short-day), ‘Crystal Wax’
- Red/Purple: ‘Red Candy Apple’ (intermediate), ‘Mercedes’
You can start onions from seed, sets (small bulbs), or transplants. Seeds offer the most variety but take the longest. Sets and transplants give you a head start, which is especially helpful if you missed the fall planting window.
Step-by-Step Planting Guide
Follow these steps to get your onions off to a strong start.
- Prepare the Soil: Onions need loose, well-draining soil rich in organic matter. Work in several inches of compost a few weeks before planting. A soil pH between 6.0 and 7.0 is ideal.
- Planting Depth & Spacing: Plant seeds ΒΌ inch deep. For sets and transplants, plant so the tip is just barely visible above the soil. Space them 4-6 inches apart in rows 12-18 inches apart. Crowding them will result in smaller bulbs.
- Watering: Water thoroughly after planting. Keep the soil consistently moist but not soggy. Drip irrigation is excellent for onions, as it keeps foliage dry and prevents disease.
- Feeding: Onions are moderate feeders. Apply a balanced fertilizer at planting and side-dress with a nitrogen-rich fertilizer every 4-6 weeks until bulbs begin to form.
Common Growing Challenges
Watch out for a few typical issues. Onion thrips are tiny insects that can cause silvery streaks on leaves. Blast them off with water or use an insecticidal soap. Avoid overhead watering to prevent fungal diseases like downy mildew.
Weeds are fierce competitors for onions shallow roots. Mulch lightly with straw or grass clippings to supress weeds and retain soil moisture. Just keep the mulch away from the direct base of the plants.
Timing Your Harvest for Perfection
Knowing when to harvest is as crucial as knowing when to plant. Here’s what to look for:
In late spring or early summer, you’ll notice the onion tops start to yellow and flop over. This is a natural sign that the plant is diverting energy to the bulb. At this point, stop watering. This helps cure the bulbs in the ground.
Once about half to two-thirds of the tops have fallen over, it’s time to harvest. Gently lift the bulbs from the soil with a garden fork. Be careful not to bruise or puncture them, as this leads to rot in storage.
Curing and Storing Your Onion Harvest
Proper curing is essential for storage. Don’t skip this step! Lay the harvested onions in a single layer in a warm, dry, well-ventilated place out of direct sun. A garage, covered porch, or shed is perfect.
Let them cure for 2-4 weeks until the necks are completely tight and dry and the outer skins are papery. After curing, trim the roots and cut the tops down to about 1 inch. Store them in mesh bags or a single layer in a box in a cool, dry, dark place. Well-cured intermediate and short-day onions can last for several months.
Northern California Onion Planting FAQ
Can I plant onions in spring in NorCal?
Yes, but only if you use short-day varieties and plant them as early as possible (February-March). Spring-planted onions will be smaller and must be used quickly, as they don’t store as well.
What happens if I plant onions too late?
Late-planted onions won’t have enough time to develop a large root system before bulbing begins. This results in disappointingly small bulbs. Its a common mistake to avoid.
How do I get my onions to grow bigger?
The key is giving them a long, cool growing season. Plant on time in fall/winter, ensure excellent soil fertility, provide consistent moisture, and give them enough space. Thin any seedlings that are too close together.
Can I grow onions in containers?
Absolutely. Choose a container at least 10-12 inches deep. Use a quality potting mix and ensure it has excellent drainage. Container onions may need water more frequently and might produce slightly smaller bulbs, but they can still do very well.
By following this regional schedule and choosing the right varieties, you’ll be well on your way to a plentiful harvest. Remember, the secret to large, storable onions in Northern California is getting them in the ground during the cooler months. With a little planning now, you’ll enjoy the rewards of your own homegrown onions for month to come.