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GREEN-Seeds.com
vegetables & herbs
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FARMER'S
BOOKSHELF
An
information system of crops in Hawaii
Department of Horticulture
University of Hawaii at Manoa
ONION
Climate
 Bulb or dry onions are
classified into three major groups based on day-length requirements: short-day,
medium-day, and long-day. Only the short-day and medium-day length types
can be grown successfully in Hawaii, provided they are planted at the appropriate
time of the year. For example, short-day length varieties planted during
the summer months will result in premature bulbing and small bulbs. Short-day
length varieties should be seeded from September to March. Medium-day length
varieties should be seeded from March to May. Varieties requiring long-day
length (13 hours or more) to bulb are not adapted in Hawaii.
Short-day mild
varieties include Yellow Granex hybrid, Tropic Ace hybrid, Early Texas Grano
502, Excel, and Yellow Bermuda. "Maui" onions would include any of these
varieties grown under Maui conditions. Short-day pungent varieties are Awahia
and Red Creole. Medium-day length varieties include Early Harvest hybrid,
Amber Express hybrid, Pronto-S hybrid, and San Joaquin.
Other onion types
commonly grown are scallions, Rakkyo (Rankyo), green onions, and shallots.
Scallions are bulb onions harvested before maturity when the bulbs measure
1 to 2 inches in diameter. The top growth is still green and upright. The
bulb portion is used for green salads and is very mild and sweet at this
stage of growth. Rakkyo is grown for its small bulbs which are used for
pickling. The growth habit is similar to the shallot, but the flavor and
odor are quite different. Planting is by means of sprouting bulbs (no seeds
available) from November through February. A single bulb will divide into
several tillers until bulb formation begins in June and July. After bulb
formation, the top growth will die down completely, usually from August
to September.
Green onions are grown
for their white stems and green leaves. Only the multiplying or dividing
types of onion and shallot are grown in Hawaii for green onion purposes.
There are two types: the small-leaved and the large-leaved (futo-negi) strains.
Propagation of the small-leaved strains and local strains of shallot is
by use of stem divisions or sets. The local strains of green onion can be
planted year round. Hawaiian shallots should be planted from September to
May as the top growth dries out soon after small bulb formation in late
summer. Futo-negi types are propagated by seed.
Cultivars
Also see section on Climate.
Green
onions are grown for their white stems and green leaves. Only the multiplying
or dividing types of onion and shallot are grown in Hawaii for green onion
purposes. There are two types: the small- leaved and the large-leaved
(futo-negi) strains. Propa gation of the small-leaved strains and local
strains of shallot is by use of stem divisions or sets. The local strains
of green onion can be planted year round. Hawaiian shallots should be
planted from September to May as the top growth dries out soon aft er
small bulb formation in late summer. Futo-negi types are propagated by
seed.
Seed Availability
Seeds
of Awahia onion are available from the Department of Horticulture of the
University of Hawaii and some garden shops. Seeds of other bulb onions
may be available at garden shops or from mainland seed companies. Sets
or sprouting bulbs of shallots and Rakkyo may be available at some garden
shops. Seeds of the large leaved type of green onion are available from
mainland or orient seed companies.
Culture
Cultivation and Irrigation
Onions
are sensitive to weed competition. Weed whenever necessary or as soon
as weeds begin to emerge. Onions are shallow rooted and require a steady
supply of moisture. Insufficient water will cause more damage to onions
than an excess of water. Irrigati on should stop when bulb formation is
complete and when the top growth begins to fall over. This will aid in
preventing soft rot damage to the bulb.
Disease Control
Rust
and purple blotch are common diseases attacking the foliage of onions.
Maneb, zineb, and copper fungicides give adequate control of these diseases.
Bulb onions are susceptible to soft rot bacteria. Bulbs should be pulled
when mature and allowed to cu re in a dry, well-aerated place.
CAUTION:
When using pesticides, always read the label and follow the directions
carefully.
Soil Management and Fertilization
Onions
thrive in well-drained, slightly acid to neutral, high organic matter
content soil. Composts or manure can be applied at 10 to 20 pounds per
100 square feet to improve the soil condition and fertility. Onions are
susceptible to nematodes. If nemato des are present, the soil should be
treated with a non-bromide containing nematicide prior to planting. Apply
a general garden fertilizer, such as 10-30-10, at 2 to 3 pounds per 100
square feet. Supply the fertilizer in two applications, half at planting
time and the other half 6 weeks later. Another application can be made,
12 weeks later or prior to bulb formation of l/2 to 1 pound of sulfate
of ammonia to enhance bulb size.
Harvesting
Green
onions can be harvested 50 to 60 days after planting. It is advisable
to harvest the whole plant and replant rather than remove the top growth
and leave the root portion in the soil. The succeeding crops from old
roots often become smaller and less productive. Bulb onions require from
90 to 120 days from sets or 150 to 160 days from seeds if short-day length
varieties are planted. Medium-day length varieties require from 110 to
130 days to harvest from seeding. Bulb onions need complete drying and
c uring for long storage life. Yellow Granex and other mild-flavored short-day
onions are poor keepers while the pungent Awahia and Creole types are
good keepers.
Insect Control
Common
insect pests of onions are thrips, aphids, leaf miners, and the larvae
of the leek or onion moth. These insects can be controlled to some degree
with diazinon and malathion through a regular spray schedule. The use
of a spreader-sticker will greatl y enhance the effectiveness of the insecticide.
However, once the larvae of the leek moth have begun feeding inside the
leaf, the only effective control would be to remove and destroy infested
leaves.
Planting
Bulb
onions can be propagated by planting 1 ounce of seed or 400 sets (small
bulbs 1/4 to 1/2 inch in diameter) per 100 foot row. Green onions are
planted at 400 sets per 100 foot row. Seeds should be planted at a depth
of l/2 to 3/4 inch. Spacing between rows should be from 12 to 15 inches.
Plants should be thinned to provide a spacing of 3 to 4 inches between
plants.
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Green - Seeds Co., Ltd.
81/10B Ho Van Hue Street, Phu Nhuan District, Ward 9, Ho Chi Minh City, Vietnam
Tel: +84 (8) 847 6901 - Fax: +84 (8) 844 1392 - Email: info@green-seeds.com
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