You may be looking for Perennial Onion Cultural Notes for information on potato and multiplier onions and shallots.
Dry Bulb Onions
Culture: Onions often only have a short window of time to grow before heat and/or lengthening days
cause bulbs to stop growing and start drying down. To encourage fast growth, plant large, healthy seedlings
into fertile, weed-free soil as early as soil can be worked. Onions require light, fertile, well-drained
soil with lots of organic matter. Maintain soil pH 6-7. Soil that is too acid or alkaline will cause slow
growth and late maturity. Onions are heavy feeders requiring abundant potassium and phosphorous for
good bulb formation. Nitrogen should be abundant during the period of active leaf growth. Onions and
weeds do not mix. Experiments have shown yield reductions of 4% per day in the presence of weeds,
or 50% reduction of yield in 2 weeks. Cultivation should be shallow since onion roots are near the soil
surface. A layer of organic mulch will help suppress weeds and will aid in maintaining moisture and nutrient levels.
Transplanting: Sow seeds indoors, 1/4 in. deep in flats in January through mid-March and
transplant outdoors 3-4 in. apart in rows 12-16 in. apart. Do not prune the tops because the harvest will be significantly decreased. To grow the largest bulbs possible, in areas with cold winters onions may be
started ~mid-November: in a cold frame or in the greenhouse, sow a thick batch of seeds, then transplant
to garden around late February or as soon as soil can be worked.
Harvest: When most
of the tops have fallen over, pull onions, cure in partial shade for 2-3
weeks until necks have thoroughly dried. Clip tops to within 1" of the
bulb. Breaking over the tops by hand to accelerate harvest harms the
keeping quality of some varieties and helps the keeping quality of other
Pests and Diseases: Practice crop rotation of at least 3 years
to control pests and diseases. Compost all onion residues.
Long Day (LD) and Short Day (SD) Types: Varieties are designated as LD or SD.
LD types begin to form bulbs when day length is 14-16 hours. Plant LD types in spring
from Virginia northward. Not all LD types can bulb up as far South as Virginia, but ours can. SD types
begin to form bulbs when day length is 10-12 hours. SD types can be spring or fall-planted in Virginia,
and fall-planted in the South. If started in a greenhouse, or started in the fall and kept refrigerated as sets, SD onions can be grown to small bulbs in the North.
Seed Savers: Isolate varieties by a minimum of 150'. For pure
seed, cage plants or isolate by 1/4 to 1/2 mile.
Packet: 3 g (about 700
seeds) sows 50' direct seeded or 245' as transplants.
Dry Bulb Onion varieties
Bunching onions are perennial onions which divide at ground
level in the same manner as multiplier onions. Unlike potato
onions they do not form large bulbs. The bases of bunching onions
are slightly enlarged, like scallions. Once established, clumps need
only be divided periodically.
Culture: See Cultural Notes for bulb
onions from seed. For easiest weeding, space clumps of 10 seeds
6-12" apart. Bunching onions are cold-hardy and may be left in
the ground year-round where the ground doesn't freeze. Where
the ground does freeze, most varieties should be transplanted into
a greenhouse or cold frame and moved out again in the spring.
Packet: 1g (about 450 seeds) sows 25'.
Preventative Medicinal Effects: Onions are a rich
source of quercetin, a natural substance which suppresses
the proliferation of some types of malignant
cells. Red and yellow varieties may contain
up to 10% of their dry weight as quercetin and
enthusiastic onion eaters have a lower rate for certain
types of cancers. White varieties contain little
or no quercetin.
Bunching Onion varieties
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