How to Grow Spanish Onions: A Guide for Flavorful Harvests

how to grow spanish onions

Spanish onions, with their large size and mild sweetness, are a favorite among home gardeners and chefs alike. If you haven’t explored growing your own onions, the Spanish variety is a great place to start. With a bit of knowledge and care, you’ll be enjoying these delicious onions straight from your garden!

Getting Started: Seeds vs. Bulbs (Sets)

To begin with, choose between the two primary ways to grow Spanish onions:

  • From Seed: Starting from seed offers the most variety but takes longer to reach harvest.
  • From Bulbs (Sets): These are essentially baby onions. Planting bulbs is faster and easier, especially for first-time growers.

Choosing the Right Time to Plant

Spanish onions are a long-season crop, meaning they take a while to mature. Timing is crucial for success:

  • Cool Climates: In areas with cold winters, plant seeds indoors early in the year (about 10-12 weeks before the last frost). You’ll transplant the seedlings outdoors when the weather warms up.
  • Mild Climates: In regions with mild winters, you can sow seeds directly outdoors in the fall or plant onion sets in early spring.

Preparing the Perfect Spot for Your Onions

Onions love sunshine and well-drained soil:

  • Full Sun: Choose a spot that gets at least 6-8 hours of direct sunlight daily.
  • Fertile, Loose Soil: Onions prefer fertile, well-draining soil. To enrich your soil, amend it with aged compost or well-rotted manure before planting. Aim for a ratio of about one-third compost or manure to two-thirds existing soil. This will provide your onions with essential nutrients and improve drainage.
  • Soil pH: Aim for a soil pH between 6.0 and 6.8.
planting of onion bulbs

Planting Your Spanish Onions

  • From Seeds:
    • Sow seeds indoors about ¼ inch deep. Keep the soil moist and warm (around 70°F/21°C) for optimal germination.
    • Once seedlings sprout, thin them to about 2-4 inches apart. Transplant outdoors when they’re a few inches tall and the weather has warmed.
  • From Bulbs (Sets):
    • Plant bulbs slightly pointed end up, about 1 inch deep and 4-6 inches apart.
    • Water thoroughly after planting.

Caring for Your Spanish Onions

  • Watering: Water regularly, especially during dry periods. Aim for about 1 inch of water per week. Onions have shallow roots, so consistent moisture is crucial.
  • Weeding: Keep the area around your onions weed-free. Weeds compete for resources and can hinder growth.
  • Fertilizing: A light application of balanced fertilizer a few weeks after planting can give your onions a boost.

How Long Do Spanish Onions Take to Grow?

Spanish onions typically take around 100-120 days to mature from seed and slightly less when grown from sets. Patience is key!

harvesting on spanish onions

Harvesting Your Onions

When the onion tops start to turn yellow and fall over, it’s harvest time! Here’s how:

  1. Curing: Gently loosen the soil around the onions and allow them to cure in the sun for a few days. This helps dry the outer skin for longer storage.
  2. Trimming: Trim the tops and roots off your onions.
  3. Storing: Store cured onions in a cool, dry, and dark place. A mesh bag or basket allows for airflow and can help with preservation.


Happy onion growing!

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