Purple onions offer a distinctive color and versatile flavor, making them popular for various culinary uses. Growing them at home provides fresh, flavorful ingredients for salads, grilling, and cooking.
Choosing and Preparing for Purple Onions
Selecting the right purple onion variety is important, as onions are sensitive to day length. Long-day varieties (14-16 hours daylight) suit northern regions, while short-day onions (10-12 hours daylight) thrive in southern climates, often planted in fall. Intermediate-day onions (12-14 hours light) perform well in transitional zones.
Purple onions need a sunny location with at least 6 to 8 hours of direct sunlight daily for proper bulb development. Good air circulation also helps prevent fungal diseases.
Purple onions thrive in loose, well-draining soil rich in organic matter, with a pH between 6.0 and 7.0. Amend heavy clay soils with compost or aged manure to improve drainage, and sandy soils to retain moisture. Incorporate several inches of aged compost or well-rotted manure into the top 6-8 inches of soil before planting.
Planting Purple Onions
Purple onions can be planted using seeds, sets, or transplants. Starting from seeds offers a wider variety selection and is economical, though it requires a longer growing period. Seeds can be direct-sown outdoors in early spring (1/4-1/2 inch deep) or started indoors weeks before the last frost. When direct sowing, space seeds 1/4 inch apart, later thinning to 3-4 inches.
Onion sets (small, dormant bulbs) offer a quicker path to maturity and are easier for beginners. Plant them 1-2 inches deep and 2-3 inches apart in early spring. While convenient, sets may not produce bulbs as large or long-storing as those from seeds or transplants.
Transplants are young onion plants that balance seed variety selection with faster growth. When planting, bury roots and about 1 inch of the lower plant portion, ensuring the neck isn’t too deep to prevent rot. Space transplants 6 inches apart in rows for bulb expansion. Water thoroughly after planting to establish them.
Ongoing Care for Purple Onions
Consistent moisture is important for large, healthy purple onion bulbs. Onions need about 1 inch of water per square foot per week, including rainfall. Water thoroughly during dry periods to ensure the shallow root system receives adequate moisture. Avoid overwatering or waterlogged conditions, which can lead to rot and disease.
Onions are heavy feeders and benefit from regular fertilization. Apply a nitrogen-rich fertilizer early to support foliage. As bulbs swell, switch to a balanced fertilizer or stop nitrogen applications to encourage bulb formation. Over-fertilizing with nitrogen near harvest can result in soft bulbs and poor storage quality.
Maintain a weed-free environment, as weeds compete for water and nutrients, reducing bulb size. Use shallow cultivation to avoid damaging the onion’s shallow root system. Apply organic mulch (straw, grass clippings) to suppress weeds, conserve moisture, and regulate soil temperature. Pull mulch back from developing bulbs as they emerge to prevent rot.
Purple onions can face pests like onion thrips and maggots, or fungal diseases. Crop rotation helps disrupt pest and disease cycles. Ensure good air circulation through proper spacing to reduce fungal issues. Selecting disease-resistant varieties can also minimize problems.
Harvesting and Storing Purple Onions
Harvest purple onions when their tops begin to yellow and fall over, typically 90-120 days after planting. This indicates bulbs have finished expanding. Stop watering plants a week or two before harvest to prepare bulbs for curing.
Curing prepares onions for long-term storage by drying their outer layers and necks. After harvest, gently pull bulbs, leaving tops attached. Spread them in a warm, dry, well-ventilated area. Curing takes two to four weeks, until the outer skin is papery and the neck is dry.
Once cured, trim dried tops to about 1 inch above the bulb and remove loose outer skins. Store cured onions in a cool, dark, dry location with good air circulation. Mesh bags or slatted crates work well. Ideal storage temperatures are 32-40°F. Stored correctly, purple onions can maintain quality for several months.