Growing onion in zone 8b

Short-day onions in zone 8b are planted in fall, typically mid-September through November, as transplants or sets. Plants establish through winter, then begin active bulbing as day length climbs past 10 to 12 hours in late February and March. Harvest typically runs from mid-April through early June depending on planting date and density.

Zone 8b's last frost generally falls between mid-February and mid-March. Onion plants are bulbing aggressively during that same window of lingering frost risk. Established plants tolerate light frosts without damage, but temperatures below 20°F can injure bulbs that have begun swelling noticeably. Row cover is a reasonable precaution during hard freeze events in the cooler northern portions of the zone.

The most significant management adjustment in zone 8b is nematode pressure, particularly in sandy, well-drained soils common across the region. Root-knot nematodes stunt root development and reduce final bulb size. Rotating onions with non-host crops (grasses, sweet corn) for at least two seasons reduces soil populations; resistant short-day varieties are limited, so rotation is the primary tool.

Onion White Rot is a persistent fungal problem under zone 8b's humid spring conditions. The pathogen survives in soil for decades, so planting in fields with no prior history of the disease is more effective than fungicide applications alone. Adequate plant spacing and drip irrigation rather than overhead watering reduce the leaf wetness that favors disease spread. Timing harvest before sustained summer heat arrives also limits late-season rot losses.