Alliums punish impatience more than almost anything else in the garden. A tomato transplanted two weeks late still gives you tomatoes. An onion transplanted two weeks late gives you a golf ball. The reason is that onions don’t bulb on a schedule you control — they bulb when day length hits a threshold written into the variety. Everything you do before that date determines bulb size. Everything after is just finishing.

That single fact reorganizes how you plan the whole family. Leeks, shallots, and garlic each have their own quirks, but the planning logic is the same: build the plant first, then let the day length do its work. This guide covers onions from seed, leeks from the long haul, and shallots as the crop most small growers overlook.

Day Length Is the First Decision, Not the Last

Onion varieties are sorted into three bulbing categories based on the hours of daylight that trigger bulb formation. Get this wrong and no amount of good soil will save the crop.

  • Short-day (10–12 hours) — bulb early, suited to roughly below 35°N. Varieties like Texas Early Grano and Red Creole. Planted in fall in the South, harvested spring. Grown in the North, they bulb in May while still tiny.
  • Intermediate or day-neutral (12–14 hours) — the widest usable range, roughly 32°–42°N. Candy, Superstar, Cabernet. If you don’t know your latitude band, these are the safest trial.
  • Long-day (14–16 hours) — above about 37°N. Copra, Patterson, Walla Walla, Redwing. These are the storage onions — Copra and Patterson routinely hold 8–10 months in a cool pantry.

Storage life tracks pungency, not variety hype. Sweet onions — Walla Walla, Ailsa Craig, most short-days — hold six to eight weeks because the sulfur compounds that make an onion sharp are also what keep it from rotting. Plan for sweet onions as a summer eating crop and long-day pungent types as your January inventory. Growing only sweets and expecting winter storage is the most common allium disappointment.

Pick your latitude band once, write it down, and stop re-litigating it every February. The varieties change; the day length at your location does not.

Starting Onions and Leeks From Seed

Onion seed is short-lived — germination drops noticeably after one year and sharply after two. Buy fresh annually. For transplants, count back 10–12 weeks from your intended field date, which for long-day onions in zones 4–6 means sowing indoors in late January through mid-February.

Sow densely: 1/4 inch deep, roughly 10–12 seeds per inch in an open flat, or 3–4 seeds per cell in 50-cell trays if you want to plant clumps. Germinate at 70–75°F, then drop to 60–65°F once up. Alliums tolerate root disturbance far better than cucurbits, so bare-root separation at transplant is fine.

Trim the tops when seedlings reach 5 inches, cutting back to about 3 inches. Do this two or three times during the indoor phase. It sounds brutal and it works — trimming diverts energy to roots, stops the flop that tangles flats, and produces a stockier transplant. Aim for pencil-lead thickness, never pencil thickness: transplants thicker than 1/4 inch at the base have a higher rate of bolting after a cold snap.

Leeks follow the same protocol but start earlier, 12–14 weeks out, because they need 100–120 days in the field after transplant. They are the crop to start first and think about last.

Transplanting and Spacing That Matches Your Market

Onion transplants go out 4–6 weeks before your last frost date — young alliums take 28°F without damage, and early planting is what buys bulb size before the day-length trigger fires. Set them 1 inch deep, no deeper; burying the growing point slows establishment and can bury the developing bulb where it rots.

Spacing controls size directly, which means you choose it based on what you sell:

  • 3 inches in-row — small-to-medium bulbs, maximum pounds per bed foot. Good for storage and CSA bags.
  • 4–5 inches in-row — the standard compromise, 3–4 inch bulbs most markets expect.
  • 6 inches in-row — jumbo sweets for display. Fewer onions, higher per-unit price.

Run 4 rows per 30-inch bed with 8–10 inches between rows. Leeks want 6 inches in-row, and either plant them in a 6-inch furrow or hill them progressively as they grow — blanched white shaft is what you’re selling, and each hilling pass adds an inch or two of it. Three passes spaced three weeks apart beats one deep burial, which invites rot at the base.

Record the spacing you used per bed alongside the variety. Next season’s sizing decision is only useful if you can tie this year’s bulb grade back to actual in-row inches, and memory reliably lies about it. Apps like CropsBook let you log planting density and variety per bed so the comparison is real data rather than recollection.

Ready to put this into practice? Download CropsBook on the App Store — it’s free and works offline.

Feeding: Heavy Early, Stop at Bulbing

Onions are shallow-rooted — most feeder roots sit in the top 6 inches — and they are poor competitors. They need high fertility delivered close and early.

Target roughly 120–150 lb of nitrogen per acre for a dry-bulb crop, or in garden terms about 1/4 cup of blood meal or feather meal per 10 row feet at planting, repeated every three weeks. Then stop. The cutoff is the moment bulbs begin to swell and necks start to soften — usually late June in the North for long-day types. Nitrogen after that point produces thick green necks that refuse to cure and rot in storage within weeks.

Alliums also want sulfur, both for yield and for flavor. If your soil test shows low sulfur, 20–30 lb per acre of elemental sulfur or gypsum pays for itself. Keep pH between 6.0 and 6.8; below 5.8 they stall.

Three dates decide an onion crop: transplant date, last nitrogen date, and the day you knock the tops. Everything else is maintenance.

Weeding and Water — Where Most Yield Is Lost

Onions have no canopy. They never shade the ground, so weeds compete the entire season, and research on allium weed competition consistently puts yield loss at 40–60 percent when the first six weeks go uncontrolled. The first four to six weeks after transplant matter most.

Practical approach: stale-seedbed the ground before planting (irrigate, wait 10 days, shallow-cultivate the flush), then cultivate every 7–10 days with a wire weeder or wheel hoe while weeds are at the thread stage. Hand-weed in-row once at about week three. After the plants reach 8 inches, mulch with 2 inches of straw — earlier mulching keeps the soil too cool for establishment.

Water consistently: 1 to 1.5 inches per week, delivered by drip if possible since wet foliage drives downy mildew and purple blotch. Uneven moisture during bulbing causes doubles and splits. Then cut water off when 10–20 percent of tops have fallen — continued irrigation at that stage pushes rot into the neck during curing.

Shallots: The Crop Worth Adding

Shallots sell for two to four times onion prices at market and take the same bed space. Two propagation routes:

  • From sets (divisions) — plant individual cloves 6 inches apart, 1 inch deep, in fall (zones 6+) or earliest spring. Each clove multiplies into a cluster of 4–8. Fastest route, but you carry over any virus load in your own stock.
  • From seed — varieties like Conservor and Matador. Treated as onions, 10–12 weeks indoors, single bulbs rather than clusters. Cleaner stock, more uniform, slightly longer to maturity.

Shallots cure and store like pungent onions — 6–8 months in good conditions. Save your best clusters for replanting, selecting for cluster size and no soft spots. That selection is also how you track whether a line is degrading: if average cluster count drops two years running, replace the stock with seed-grown.

Harvest, Curing, and Storage That Actually Holds

Harvest onions when 50–80 percent of tops have fallen over naturally. Don’t knock the tops down by hand to hurry it — breaking the neck mechanically opens an infection path. Lift with a fork on a dry day and leave bulbs on the bed surface for a day or two if weather allows, but shade them above 85°F; sunscald shows up as pale, soft patches that rot first.

Curing is the step people shorten and regret. Move bulbs to a dry, airy, shaded space — a barn aisle, a shed with fans, racks under a porch. Hold 75–85°F with real air movement for 10–14 days, longer in humid climates. The crop is cured when the neck is tight and papery, the outer skins rustle, and the neck doesn’t compress between your fingers. A soft neck is an onion that will be mush by November.

Then trim: roots to 1/4 inch, tops to 1 inch above the bulb, or braid the soft-necked types. Store at 32–40°F and 65–70 percent humidity in mesh bags or slatted crates, single layer where possible, never sealed plastic. Sort every three weeks and pull anything soft — one rotting bulb takes its neighbors with it.

Leeks skip curing entirely. They hold in the ground down to the low 20s and sweeten with frost; heavy-mulch them and dig as needed through winter in zones 6 and warmer. In colder zones, lift before the ground freezes solid and pack them upright in damp sand in a root cellar.

Cured means the neck doesn’t compress between your fingers. Not “it looks dry.” Not “it’s been two weeks.” Squeeze the neck.

Keeping the Records That Make Next Year Better

Alliums are the strongest argument for written records of any crop in the garden, because the feedback loop is a full year long and the critical variables are all dates. Log the sow date, transplant date, variety and day-length class, in-row spacing, the date of the last nitrogen application, the date tops fell, the cure duration, and — the one everyone skips — the date you threw out the last storable bulb. That final date is the only honest measure of whether your curing worked.

Pair it with weight harvested per bed and you can answer real questions: did the 3-inch spacing actually out-yield the 5-inch on a per-foot basis, or just produce more culls? Did the bed that got a fourth feeding store worse? CropsBook handles this kind of per-bed, per-variety logging offline, which matters when the curing shed has no signal and you’re recording as you trim. The same logic shows up across farm record-keeping generally — growers running livestock alongside vegetables use Barnsbook for herd and barn records, and anyone keeping bees for pollination tracks hive inspections in HiveBook. Different crops, same principle: the dates you didn’t write down are the ones you’ll need.

Alliums reward planning more than skill. Choose varieties matched to your latitude, start seed early enough to build a real transplant, get them in the ground while it’s still cold, feed hard until bulbing begins and then stop, keep the weeds off for the first six weeks, and cure longer than feels necessary. Do those six things and you’ll be pulling onions out of storage in March that still have tight necks and firm shoulders — which is the only review of an allium crop that counts.