Nevada · zones 5b–9a
When to plant onions in Nevada.
Sow or transplant between Mar 1 to Apr 14 in a typical year, keyed to Nevada's median last frost around May 9. A second, fall sowing fits Aug 3 to Sep 14. Dates below are state medians; your ZIP code shifts them by days to weeks.
The 2026 windows
Onions dates for a typical Nevada season.
1 · Start indoors
Jan 18 to Mar 3
About 6 weeks before set-out. Warm spot, real light.
2 · Set out
Mar 1 to Apr 14
Keyed to the ~May 9 last frost. Sow 0.5" deep, 4" apart.
Fall round
Aug 3 to Sep 14
Counted back from the ~Sep 28 first frost.
Harvest
~95 days later
~0.5 lb per plant over ~1 weeks.
Nevada spans more than one climate: Zone 6 is the most common zone, but the state runs 5b to 9a. That's why the planner works from your ZIP code's frost dates, not your zone: mountain and coastal gardens in the same state can be three weeks apart.
Nevada growing notes
Onion bulb size here depends less on soil or water than on which side of the state's long day-length divide the seed was bred for.
The clock that actually decides bulb size
An onion transplant set 4 inches apart and barely half an inch deep spends its whole season building leaves before it starts building a bulb; the trigger is daylight length, not temperature or feeding. Long-day varieties need the long summer daylight found through most of Nevada, a spread running from around Reno north toward the Idaho and Oregon lines; Walla Walla Sweet, a long-day type, suits that ground well. Near the state's southern tip, through the Las Vegas valley and the Mojave beyond it, summer days run measurably shorter, close to the line seed catalogs draw between long-day and intermediate country, so the safer bet is an intermediate type such as Candy.
Getting that choice backwards does not look like a sick plant. A long-day variety grown too far south can put up a full, healthy stand of leaves all season and never receive the signal to swell at the base, leaving nothing underground but a fibrous stem barely wider than a scallion, with no fix once underway. Check a few plants when the crop should be sizing up: tops that still look strong while the neck stays soft and pencil-thin instead of firming up point straight at next year's seed catalog, not this year's feeding schedule.
Two windows, and a bulb that forms on schedule whether the plant is ready or not
Nevada supports both a spring-set transplant and a fall-planted crop. A spring transplant needs time to build real leaf area before lengthening days flip the plant into bulbing, since bulb size tracks how much leaf was built when that signal arrives, not how many more weeks follow. Set too late, a spring transplant still gets the same day-length cue as one set on time and bulbs early anyway, straight into a small onion without enough leaf grown to size up properly.
The fall window works best in the milder low-desert zones near 8a and 9a, where winter rarely shuts a planting down completely. Sets go into the ground in fall, hold as a modest stand through the cool months, then resume growth well ahead of a spring-set planting once weather turns, reaching the day-length trigger with far more leaf already built and a bigger bulb than the same 95 days could produce starting from nothing in spring. Further north, from 5b through 7a, a real winter kills a fall-set planting outright, so spring carries the load there instead.
What actually threatens the bulb once it is sizing up
Onion thrips do real damage before a grower notices anything, hiding down in the V where new leaves emerge from the neck and rasping at the tissue, leaving a silvery, papery streak instead of a hole. A light case costs little; a heavy one thins and yellows the leaves the bulb depends on, so pulling one plant apart at the neck partway through the season is a better check than scanning the row. Onion maggot works the opposite end and mostly threatens a young transplant, tunneling into the base and killing it outright with no warning beyond a single wilted plant.
Downy mildew shows up as a pale, sometimes purplish fuzz on the leaf, most likely during a wet spring stretch or on a planting watered overhead in the evening, since dry air keeps it from establishing most seasons. White rot breaks that pattern: the fungus works underground at the bulb's base, not the leaf surface, so Nevada's dry air offers none of the protection it gives against downy mildew. A plant that yellows and topples despite decent care is worth pulling to check the base first. Once confirmed, treat that patch of ground as off-limits to onions and garlic for good: the fungus survives in the soil as sclerotia for 20 to 40 years, far longer than any rotation a gardener would plan around, and dry air will not undo damage already there.
In Nevada: watch for
The pests that find onions here.
The short season here, about 142 frost-free days, keeps onion, bulb in front of onion thrips only briefly. One early row cover usually carries a planting through the worst of it.
Silvery streaks and curled leaf tips in hot spells.
Organic fix: Insecticidal soap or neem; hang sticky traps.
Seedlings wilt; white maggots in the bulb base.
Organic fix: Float a row cover over the row; rotate beds each year.
Pale patches with fuzzy gray growth in damp weather.
Organic fix: Space for airflow, water early in the day, spray neem.
White rot
Yellowing and dieback, then wilt; fluffy white mold at the bulb base and roots so rotted the plant lifts straight out.
Organic fix: No cure once it is in the soil. Plant clean stock, never follow onions with onions, and keep infested soil off tools and boots.
Your season math: Nevada gives onions about 142 frost-free days, and it needs roughly 95 days to a first harvest. It's a one-planting crop, so time that single sowing well.
Planting onions in Nevada: questions
When should I plant onions in Nevada?+
In a typical Nevada year, sow onions or set out transplants between Mar 1 to Apr 14, keyed to the state's median last frost around May 9. There's also a fall window: Aug 3 to Sep 14. Your exact dates shift with your ZIP code and microclimate.
When do I start onions seeds indoors in Nevada?+
Start seeds inside about 6 weeks before set-out: roughly Jan 18 to Mar 3 for a typical Nevada season.
What USDA zone is Nevada?+
Nevada spans zones 5b–9a, mostly zone 6. But frost dates, not zones, set planting time. The free planner uses your ZIP code's actual frost dates.
How many onions plants do I need?+
Depends who you're feeding. The crop page has exact counts per household size, or the free planner does the math for your family in about 60 seconds.