Growing Onions from Plants: Complete Guide to Bulbing Onions

About Our Plants

Prestarted from finest seed for flavor, texture, reliability. Arrive like little scallions; pale from shipping but green up quickly.

Daylength Types

Daylength affects bulbing more than climate. Long-day onions grow best north of San Francisco–Savannah line; short-day south of it. Day-neutral grow everywhere.

Planting & Harvest

Upon Receipt

Live plants (not sets). Plant ASAP. If delayed, cool dry area ~3 weeks on bulb energy. After planting, new roots form.

Soil Preparation

Fertile, well-balanced. Organic: rich compost. Lime if acidic. Commercial: 10-20-10, make 3″ trenches, ½ cup/10 ft row, cover with 2″ soil.

Planting

Set 1″ deep, 4″ apart. For green onions, space 2″ and pull every other before bulbing. Transplant 4–6 weeks before last frost.

Fertilizing

High nitrogen. Liquid fish emulsion 3 weeks post-plant, then every 3–4 weeks. Stop when necks soft (~4 weeks before harvest). Water in granular.

Watering

Evenly moist. More water as harvest nears.

Weed Control

Early hand-weeding/hoeing. Don't damage bulbs. Keep soil loose for expansion; don't push dirt against leaves (prevents bulbing). Light organic mulch; pull back when bulbing starts.

Diseases & Insects

Blight (pale-green→yellow leaves) and purple blotch (purple lesions) favored by dew/fog/rain. Prevention: well-drained soil, rows with prevailing winds, no windbreaks. Fungicide if persistent. Onion thrips (light brown, <1/6″) cause silvery blotches. Clean garden; insecticidal soap or pyrethrin.

Bolting

If flower stalk appears, pull and eat immediately. Caused by unexpected dormancy. Edible but stalk decays bulb in storage.

Harvest & Storage

When tops yellow and half fallen, bend rest with rake back. Diverts energy to bulb. Day later when brown, pull and sun-dry. Lay tops of one row over bulbs of next to prevent sunscald. Dry, clip roots, cut tops to 1″. Store in mesh bag/nylon stocking (knot between each) in cool dry place. Or spread on screen, not touching. Sweeter onions = higher water = shorter shelf life; eat sweet ones first.