Green Onions in Zone 7B — Northern California

Green onions are a must-grow in any Northern California garden. Their mild, fresh flavor elevates everything from tacos to salads, and they're so easy to grow. Plus, having a constant supply of homegrown green onions right outside your door is incredibly satisfying in our Mediterranean climate.

We NorCal gardeners know the challenges: drought, unpredictable temperature swings, and the ever-present worry of fire season. But with our long, 245-day growing season and careful planning, you can enjoy fresh green onions almost year-round. It's all about timing and smart watering strategies.

If you're starting your green onions indoors or have purchased seedlings, aim to transplant them outdoors from mid February through mid March. This gives them a head start before the summer heat kicks in.

Before planting, harden off your seedlings by gradually exposing them to outdoor conditions for about a week. This helps them adjust to the sunlight and temperature differences. Space the seedlings about 2-3 inches apart in well-drained soil.

Keep an eye on the weather forecast. Late frosts are always a possibility during this time in Northern California, so be prepared to cover your transplants if temperatures dip unexpectedly.

Direct sowing is the easiest way to grow green onions here. You can sow seeds directly into the garden from mid February through early September, ensuring a continuous harvest.

Prepare the soil by loosening it and adding compost. Green onions prefer well-drained soil with a soil temperature above 50°F. Sow seeds about ½ inch deep and 2-3 inches apart. Keep the soil consistently moist until germination, which usually takes about a week. For a super easy start, try planting the root ends of store-bought green onions – just stick them in the ground!

Green onions need consistent moisture, especially during our dry summers. They aren't drought-tolerant, and their shallow roots dry out quickly.

In the spring and fall, when temperatures are milder, aim for about 1 inch of water per week. During the hotter summer months, increase that to 1.5-2 inches per week. The "finger test" is a good guide: stick your finger about 2 inches into the soil. If it feels dry, it's time to water. Water at the base of the plants to avoid wetting the foliage, which can encourage fungal diseases in our low-humidity environment.

Signs of underwatering include wilting or yellowing leaves. Overwatering can lead to bulb rot. A layer of mulch, like straw or wood chips, helps retain moisture and regulate soil temperature, a must-do in our region where water conservation is key.

You can expect your first harvest of green onions around mid April if you planted early, and you can continue harvesting through late November. Green onions are typically ready to harvest about 60 days after planting, when the stalks are about pencil-thick.

You can either pull up the entire plant or cut the green stalks about an inch above the base. If you cut them, the plant will regrow, giving you multiple harvests. To encourage continued production, snip off any flower stalks that appear.

As our first frost approaches around mid- November, harvest any remaining green onions. You can chop and freeze them for later use or transplant them into containers and bring them indoors for the winter.

Here are some common problems you might encounter with green onions in your Northern California garden:

• Onion Maggots
• What it looks like: Wilting or yellowing plants, stunted growth, and small white maggots feeding on the roots and bulbs.
• What causes it: These pests thrive in moist soil.
• How to fix/prevent it: Use row covers to prevent the adult flies from laying eggs. Apply beneficial nematodes to the soil.
• Thrips
• What it looks like: Silvery streaks or spots on the leaves, distorted growth, and tiny, slender insects.
• What causes it: Thrips are attracted to stressed plants, especially during hot, dry weather.
• How to fix/prevent it: Provide adequate water and fertilizer. Introduce beneficial insects like ladybugs and lacewings. Insecticidal soap can also be effective.
• Downy Mildew
• What it looks like: Yellow patches on leaf tops with fuzzy gray-purple growth on undersides. Leaves brown and die from the bottom up.
• What causes it: Oomycete pathogen that spreads in cool, humid conditions via wind-carried spores. Different species affect different plants.
• How to fix/prevent it: Remove affected leaves immediately. Improve air circulation. Water at the base, never overhead. Copper-based fungicides for prevention. Plant resistant varieties where available.
• Pink Root
• What it looks like: Pink or reddish roots, stunted growth, and yellowing leaves.
• What causes it: A soilborne fungus that thrives in warm, moist conditions.
• How to fix/prevent it: Improve soil drainage, rotate crops, and avoid overwatering. Solarizing the soil can also help.

Northern California Specific Challenges: Our moderate-to-hot, dry summers can stress green onions, making them more susceptible to pests and diseases. Consistent watering and mulching are key to keeping them healthy. Also, be mindful of microclimates in your yard. Some areas might be hotter and drier than others, requiring more frequent watering.

Companion planting can help your green onions thrive in our NorCal gardens. Carrots are great companions because they deter onion flies, while green onions deter carrot root flies. Lettuce provides ground cover, keeping the soil cool and moist. Tomatoes and peppers benefit from green onions, which repel aphids and other pests. Beets also make good companions, as they don't compete for nutrients and can help break up the soil.

Avoid planting green onions near beans and peas, as they can inhibit each other's growth. These legumes fix nitrogen in the soil, which can be detrimental to onion development.