🧅 Onion

Allium cepa
Layers of flavor, layers of tears, zero regrets.
Sun
Full sun, 6–8 hrs
Days to harvest
100–175 days depending on type and method
Spacing
4–6 inches apart
Soil pH
6.0–6.8

How to grow

The day-length thing matters, so listen up: SHORT-DAY onions bulb when days hit 10–12 hours (the South — Florida, plant in fall for spring harvest); LONG-DAY onions need 14–16 hour days (the North, plant in spring); INTERMEDIATE/DAY-NEUTRAL split the difference. Plant the wrong type and you get beautiful green tops and golf-ball bulbs.

Easiest path: plant SETS (tiny bulbs) or TRANSPLANTS in early spring (North) or fall (South), 1 inch deep, 4–6 inches apart. From seed takes longest but gives the best varieties — start indoors 8–10 weeks before transplanting. Keep weed-free; onions compete with weeds about as well as a housecat competes with a Roomba.

Water & feeding

Steady moisture while bulbs size up — about 1 inch per week. Then STOP watering when tops start falling over; like garlic, onions cure best when they dry down. Feed lightly: worm castings worked into the bed at planting, one side-dress mid-season. Excess nitrogen late = thick necks that won't cure.

Common problems

  • Onion maggots: row cover at planting; rotate alliums; the flies find stressed seedlings by smell, so healthy transplants help.
  • Thrips: silvery leaf scars. Reflective mulch, insecticidal soap, or just tolerate light damage — bulbs usually size fine.
  • Bolting (premature flowering): caused by cold snaps on young plants. The bulb stops growing and gets woody — pull and use as green onions, then plant sets later next year.

Harvest

When half the tops have flopped over naturally, pull and cure 2–3 weeks in a dry, airy, shady spot until necks are tight and papery. Braid or bag in mesh; store cool, dry, dark. Sweet onions store weeks, pungent storage types store months — sulfur compounds are nature's preservative.

Nerdy fact: Onions make you cry because cutting ruptures cells, mixing enzymes that produce syn-propanethial-S-oxide — a volatile gas that drifts up and attacks your eyes. It's chemical warfare, evolved to deter animals from eating the bulb. It works on everyone except humans, who responded by inventing onion goggles.

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