Introduction to Onion (Walla Walla Sweet)
Walla Walla Sweet onions are a long-day, mild-flavored variety developed in Washington state. They produce large, globe-shaped bulbs with thin, golden skins and exceptionally low pungency due to their high water and sugar content. This makes them ideal for fresh eating, salads, and grilling. They require specific day-length and temperature conditions to bulb properly and are best suited to cool spring climates with long summer days.
Botanical Profile of Onion (Walla Walla Sweet)
Onion (Walla Walla Sweet) belongs to the Amaryllidaceae family. It is a biennial plant grown as an annual for its edible bulb. The plant forms hollow, blue-green leaves and stores energy in a swollen basal plate that develops into the bulb. Walla Walla Sweet is genetically selected for low sulfur content, resulting in reduced tear-inducing compounds. It matures in 100-110 days from transplant and produces bulbs averaging 4-6 inches in diameter under optimal conditions.
Soil, pH, and Climate Requirements for Onion (Walla Walla Sweet)
Walla Walla Sweet onions demand loose, fertile, well-drained soil with consistent moisture. Heavy clay soils should be amended with organic matter to prevent compaction and bulb deformation. The crop prefers full sun (minimum 8 hours daily) and cool temperatures during early growth followed by long days for bulbing.
| Parameter | Ideal Range/Value | Notes |
|---|---|---|
| Soil Type | Sandy loam to loam | Well-drained; avoid heavy clay |
| Soil pH | 6.0-7.0 | Slightly acidic to neutral |
| Temperature (Growth) | 55-75°F (13-24°C) | Cool spring for vegetative growth |
| Temperature (Bulbing) | 70-80°F (21-27°C) | Long days (>14 hours) trigger bulbing |
| Spacing | 4-6 inches between plants | Rows 12-18 inches apart |
| Organic Matter | 3-5% | Incorporate compost before planting |
Step-by-Step Planting & Propagation
Start seeds indoors 8-10 weeks before the last frost or purchase onion sets/transplants. Sow seeds ¼ inch deep in sterile seed-starting mix at 60-70°F. Harden off seedlings for 7-10 days before transplanting. Plant in prepared beds when soil reaches 50°F, spacing plants 4-6 inches apart in rows 12-18 inches apart. For direct seeding, sow ½ inch deep and thin to final spacing once seedlings reach 3 inches tall. Walla Walla Sweet requires long days (14+ hours) to initiate bulb formation, so plant in early spring in northern latitudes.
Care & Maintenance regimes for Onion (Walla Walla Sweet)
Consistent moisture and fertility are critical. Avoid drought stress during bulb enlargement. Side-dress with nitrogen-rich fertilizer early, then switch to balanced or low-nitrogen formulas as bulbs mature. Mulch with straw or compost to retain moisture and suppress weeds. Remove weeds by hand to avoid damaging shallow roots.
| Stage | Water Schedule | Fertilizer Schedule | Pruning/Thinning Schedule |
|---|---|---|---|
| Seedling (0-4 wks) | Keep soil evenly moist; 0.5 inch/week | Apply starter fertilizer at transplant | Thin to 4-6 inch spacing |
| Vegetative (4-8 wks) | 1 inch/week; avoid waterlogging | Side-dress with ½ lb N per 100 sq ft | Remove flower stalks if they appear |
| Bulbing (8+ wks) | 1-1.5 inches/week; reduce before harvest | Switch to low-N fertilizer; stop 3 weeks prior | No pruning needed |
Pests, Diseases & Organic Management
Common threats include Onion maggots, thrips, and fungal issues. Practice crop rotation and use floating row covers to exclude onion maggots. Monitor for thrips and treat with insecticidal soap or neem oil. Prevent fungal diseases like downy mildew by ensuring good airflow and avoiding overhead watering. Remove and destroy infected plants promptly.
Harvesting, Curing & Optimal Storage
Harvest when 50-75% of tops have fallen over and bulbs show mature skins. Pull gently and allow onions to field-cure for 3-7 days in dry conditions. Cure indoors at 70-80°F with good airflow for 2-4 weeks until necks are dry. Store at 32-40°F with 65-70% humidity. Walla Walla Sweets have shorter storage life than pungent varieties and are best consumed within 1-3 months.
Companion Planting for Onion (Walla Walla Sweet)
Onions pair well with carrots, Lettuce, beets, and herbs like Thyme to deter pests. Avoid planting near beans or peas, which may inhibit onion growth. Interplant with Nasturtium for aphid control. Rotate with non-allium crops annually to reduce soil-borne disease buildup.