California’s Position in Allium and Root Crop Production
California’s Central Valley is the nation’s leading producer of garlic — the Gilroy area of Santa Clara County and the San Joaquin Valley collectively produce approximately 90% of domestically grown garlic. The state also produces significant volumes of dry onions (primarily in the Imperial Valley and Kern County), and processing potatoes in the Sacramento Valley and San Joaquin Delta. Each of these crops requires post-harvest handling that is categorically different from fresh produce, with curing as an essential prerequisite to successful cold storage.
Garlic: Curing and Cold Storage Requirements
Fresh garlic must be cured before cold storage — a process that dries the outer skin layers to form a protective wrapper that seals moisture inside the clove and creates a barrier against pathogen entry. Curing takes place at 80–95°F with low humidity and high airflow for 2–4 weeks, until the neck of each bulb is completely dry and papery.
Following curing, garlic is stored at 28–32°F with 60–70% relative humidity (low humidity is critical — high humidity causes sprouting and mold). At these conditions, cured garlic has a storage life of 6–8 months. Seed garlic intended for the following season’s planting is stored separately at slightly higher temperatures (32–35°F) to avoid damage to the growing embryo.
California garlic destined for export — particularly to Asian markets where California garlic commands a premium — requires cold chain documentation and phytosanitary inspection by USDA APHIS. Garlic exported to China, Japan, and South Korea must meet strict quarantine pest requirements for allium leafminer and other pests detectable at inspection.
Dry Onion Cold Storage
Dry onions require a curing process similar to garlic — removal of field moisture by forced-air curing at 75–85°F for 2–4 weeks until necks and outer skin are fully dry. Cured dry onions are then stored at 32–34°F with 65–70% relative humidity. At optimal conditions, storage life is 6–8 months for long-day sweet onions (more prone to decay) and 8–12 months for pungent storage onions (higher sulfur content provides natural antimicrobial protection).
Carbon dioxide buildup in tightly packed onion storage rooms is a real operational concern — CO2 levels above 5% cause core decay. Adequate ventilation with outside air exchange (limited to nighttime in summer to avoid warming the room) is essential for long-term onion storage quality.
Processing Potato Storage
Processing potatoes — those destined for french fries, chips, and dehydrated potato products — require storage conditions that balance starch chemistry with disease management. Chip-stock potatoes are highly sensitive to cold-induced sweetening: storage below 50°F converts starch to reducing sugars that caramelize during frying, producing dark-colored chips. Chip-stock must be stored at 50–55°F, significantly warmer than most cold storage facilities operate.
Fresh-market and seed potatoes have different requirements — 38–40°F for fresh-market red and yellow varieties (lower temperature than chip-stock) and 38–40°F with specific humidity management for seed potatoes. The diversity of temperature requirements within the potato category means that a cold storage facility serving potato shippers must have multiple independently controlled temperature zones.
