Winter onions wake up before anything else in the garden. If you back them early with the right kind of feed, they pay you back with hefty bulbs that store cleanly into next season. Here is exactly how to time and mix the good stuff so the plants build strong tops first and then shift gears into fat, dense, keeper bulbs.
First two weeks after the snow: give them nitrogen
The early game is all about leaf power. More leaf means more bulb. In the first two weeks after the snow recedes, push a nitrogen feed. If the soil still feels cold and sluggish, stir 1 tablespoon of magnesium sulfate into your mix per 10 liters of water — that little tweak helps onions use nitrogen efficiently even in low temperatures. In dry weather, water the bed first, then feed. Apply solutions straight to the root zone and keep fertilizer off the leaves.
- Urea: 20-25 g per 10 L of water — a clean, fast start.
- Ammonium nitrate: 10-15 g per 10 L — keeps working in cool weather.
- Organic route: well-rotted manure at 1:10 with water, or poultry manure at 1:15.
Ten days later: a foliar nudge
About 10 days after that nitrogen feed, spray the foliage with a biostimulant (something like "Novosil" or a similar product). This tones up disease resistance and helps the plants ride out any temperature swings.
When bulbs begin to form: switch to phosphorus and potassium
As soon as you see bulbs starting to set, pivot to phosphorus and potassium. These two drive size, density, and long storage. The straightforward choice is monopotassium phosphate at 10-15 g per 10 L of water. If you worked superphosphate into the soil last fall, spring feeding can focus on potassium alone — potassium sulfate does the job. Prefer an organic lean? Steep 1 cup of wood ash in 10 L of water for 24 hours and use that infusion.
Free, effective: green fertilizer from weeds
No need to waste a good weed. Pack a plastic or wooden barrel about two-thirds full with fresh weeds (nettle, dandelion, comfrey are perfect), top up with water, cover, and let it ferment for 5-10 days. Metal containers can oxidize and spoil the brew, so skip those. Dilute the finished concentrate 1:8-10 with water and pour it at the base of the onions.
Late to the party? Salvage the season
If that early nitrogen window slipped by, record-breaking yields become unlikely, but you can still steady the crop. Give a half-rate nitrogen feed — 10-12 g of urea per 10 L of water — and pair it with a foliar feed so the plants absorb nutrients faster. Put most of your effort into phosphorus and potassium at this stage; those can go on even if you are a bit behind schedule.