How to Grow Pacific onion

soil preparation

Prepare well-draining soil rich in organic matter. Work the bed to a depth of 8-10 inches, breaking up compacted earth. Incorporate 2-3 inches of compost or well-rotted manure into the top 6 inches. Onions prefer slightly acidic to neutral soil with a pH range of 6.0-7.0. Ensure drainage is excellent, as onions are susceptible to rot in waterlogged conditions. If your soil is heavy clay, add sand and organic matter to improve texture. Allow beds to settle for 1-2 weeks before planting.

planting steps

watering

Onions require consistent moisture, especially during the bulb-formation stage. Provide 1-1.5 inches of water per week through rainfall or irrigation during the growing season (spring through early summer). Water deeply to reach 6 inches into the soil—shallow daily watering produces weak root systems. Reduce watering frequency as bulbs mature and approach harvest (when tops begin to yellow and dry). In the final 3-4 weeks before harvest, water only during drought stress. Check soil moisture by inserting your finger 2 inches into the soil; if it feels dry, water thoroughly. Overwatering causes soft, poorly-storing bulbs and increases disease susceptibility. Watch for signs of underwatering: yellowing leaves, small bulbs, and stunted growth. Drip irrigation or soaker hoses are superior to overhead watering, as they keep foliage dry and reduce fungal disease.

feeding & fertilizer

Begin with a balanced fertilizer mixed into the soil during bed preparation. Use a 10-10-10 or 5-10-10 NPK ratio fertilizer at the rate recommended on the package for your bed size—typically 2-3 pounds per 100 square feet. Once plants are established and actively growing (3-4 weeks after planting), apply a nitrogen-rich side-dressing of 10-0-0 or similar formula every 3-4 weeks. Use 1 tablespoon per plant, applying it 3 inches away from the stem to avoid burning. Stop fertilizing 4-6 weeks before harvest to allow bulbs to mature and cure properly. Excess nitrogen late in the season produces soft bulbs with poor storage life. If using compost as your primary amendment, typically no additional feeding is needed if the compost is well-established.

pruning & training

Pacific onions require minimal pruning. Remove any yellowing or diseased leaves promptly to reduce pest and disease pressure. Do not cut or trim green foliage during the growing season, as leaves are essential for bulb development—each leaf supports bulb layer formation. If flower stalks appear (onions occasionally bolt), remove them immediately by pinching or cutting, as flowering diverts energy from bulb growth. In the final 2-3 weeks before harvest, resist the urge to trim foliage even if it looks shabby; the plant is directing energy into curing the bulb.

storage & preservation

After curing is complete, trim the dried tops to 1 inch above the bulb, or leave them intact if braiding is desired. Trim roots to 1/4 inch. Store bulbs in a cool (45-55°F), dry (50-60% humidity), dark location with good air circulation—a basement corner, root cellar, or garage works well. Do not store in plastic bags; use mesh bags, wooden crates, or open shelving that allows air movement. Properly cured and stored Pacific onions keep 4-6 months, sometimes longer depending on storage conditions and cultivar. Check stored onions monthly and remove any that show soft spots, mold, or sprouting. Do not store onions near potatoes; potatoes release ethylene gas that accelerates sprouting. For extended storage, some gardeners layer bulbs in layers separated by dry sand or newspaper in a cool location.

common mistakes to avoid

• ✗Overwatering late in the season—this produces soft, poorly-storing bulbs with short shelf life. Stop deep watering 4-6 weeks before expected harvest and reduce frequency significantly. Only water if drought stress appears.
• ✗Harvesting too early before tops naturally yellow and fall over—immature bulbs don't cure properly and won't store well. Wait for natural foliage senescence as your primary harvest cue.
• ✗Improper curing or storage—bulbs cured in excessive heat, high humidity, or direct sunlight sprout prematurely or develop decay. Cure in a dry location at 70-80°F with good air circulation for at least 2-3 weeks.
• ✗Crowding plants—onions need space for proper bulb development. Spacing smaller than 4-6 inches produces stunted bulbs unsuitable for storage.
• ✗Leaving tops on too long after curing—excessively long necks provide entry points for pathogens and increase disease during storage. Trim to 1 inch for storage.
• ✗Cutting or trimming green foliage during growth—each leaf supports bulb development. Foliage removal reduces yield and bulb size. Cut only diseased or damaged leaves.