Growing Food: A Guide to Food Production

_ var. cepa—the Common Onions. Commercially the most important group of

onions. This type of onion has been selected for thousands of years, so
botanically they are now highly variable. Includes the Spring or Bunching
Onions.
_

reproduction:
Potato (Multiplier) Onion—only flowers rarely, but has lateral bulbs which
produce separate bulbs and tops in the second year;
Ever-ready Onion, Welsh Onion (The name comes from the German welsche
“foreign”),
Japanese Bunching Onion, Scallions (a name also used for Shallots) or Ciboule.
_

are not important commercially.

The description below refers to the Common Onion Allium cepa var. cepa. Hybrid
seed of this species is widely used, while other Allium species mainly rely on non-
hybrid seed.

PLANTING
Propagation: either by seed or by dry bulbs, or “sets”. When by seed, seedlings are
often transplanted at about 10–12 weeks (sometimes pruned, tops and roots, to 15–25
cm long). Small sets have a tendency to bolt less readily than larger sets.
Germination: viability falls rapidly in hot, humid conditions—may be 0% in less
than a year. F1 hybrid seed adapted to a wide range of conditions is readily
available.
Soil: soil should have plenty of nutrients in the upper 10 cm or so profile and should
retain moisture well. Onions adapt to most soils provided moisture is not limiting.
“Intermediate tolerance” to soil acidity. The soil should ideally be well manured or
composted some months before the seed or sets are planted. In heavier soils, coarse
sand can be placed under each set.

Other crops: they make good companion crops to other vegetables such as carrots,
as their smell can keep away harmful insects such as the Carrot Root Fly.

GROWTH CONDITIONS
Day length: sensitive to photoperiod. Most varieties are long-day, some are short-
day and some day-neutral. The long-day varieties that are adapted to temperate
regions will not form bulbs in the tropics, where short-day varieties are needed. The
photoperiod does not affect bolting, which occurs as a function of the onion variety
and the temperature. If “new” (previously untested) varieties of onions are

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Spacing: 25–40 cm between rows for bulbs, 10 cm for salad onions; 7.5 – 10 cm

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Seed rate: 3.5–4.5 kg/ha when transplanted, 4–6 kg/ha when direct seeded. Approxi-
mately 250,000 seeds/kg.

Depth: 1–2 cm.

between plants.

GROWING FOOD – THE FOOD PRODUCTION HANDBOOK

var. aggregatum—three types, which form lateral bulbs or shoots for vegetative

var. proliferum the Tree Onion or Walking Onion which have only small and

undeveloped ground bulbs, but instead produce “bulbils” on the flower heads.

These bend down to the ground, take root and so propagate in this way in a

circular form around the parent plant. No seed is normally produced. Tree onions