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Re: The Cultivation of Onions

THE CULTIVATION OF ONIONS


With the possible exception of potatoes it is very probable that the onion
family are more used in the kitchen than any other vegetable.

It is widely thought that the wild onion originated in Central Asia and
references to its cultivation and dietetic properties can be traced back as
far back as the ancient Egyptians. To the present day the onion remains a
very popular vegetable, however the quantity produced in the British Isles
falls short of requirements and considerable quantities need to be imported
each year.

The Allium family - which includes leeks, shallots, and garlic - are
members of the lilaceae which are described as hardy bulbs many of which
are grown for their ornamental flowers. Such plants can be grown in any
ordinary soil which, preferably, should be of a light sandy nature. They
prefer a light, sunny position in which to grow.

In British gardens the bulb onion - Allium cepa - can be cultivated in two
ways; by sowing seed, or by planting sets which are specially prepared
immature bulbs.

Onions grown by exhibitors are frequently grown in a permanent bed so the
fertility of the soil may be built up over a number of years, however, for
the production of more normal sized onions for kitchen use it is
recommended that the site for growing onions is changed annually.

To grow onions an open sunny site is required with good drainage. The plot
should be thoroughly dug the previous autumn simultaneously incorporating a
liberal quantity of manure in the process. If the soil indicates acidity
liming may be necessary to produce a pH value nearer to neutral. (Note that
onions prefer a pH value between 6.0 and 7.0.). All onions require a
fertile and free draining site, however onion sets will tolerate less
demanding cultivation conditions requiring neither the fine soil texture,
nor the high organic material content demanded by seed sown onions.

Before sowing, or planting onions it is recommended that a traditional
‘onion bed' is prepared. Initially a general purpose fertiliser, e.g.
Growmore, is applied to the soil surface when it is reasonably dry during
the spring. The area is then treaded and raked over again to produce a fine
and even tilth. Seed may then be sown in drills 0.5 inches deep and 9
inches apart. If the soil is dry the drills should be carefully watered
before sowing the seed. In the case of onion sets these should be planted
at a distance of 4 inches in rows 9 inches apart. The soil should be well
firmed around the set.

Onion sets planted in late February to the end of April will mature and
produce eating quality bulbs between July and September. Seed sown in late
February to early April will - depending upon geographical location -
produce crops between August and September.

During the lifetime of the onion any flower stems which develop as the
plant matures should be broken, or pinched off to prevent the onion from
running to seed and thus preventing the bulb from developing. (It should be
noted that the onion is essentially a biennial plant producing the bulb - a
storage organ - in the first year and producing flowers and seed in the
second year.). Mulching the crop can assist in reducing the rate of water
loss from the soil particularly during periods of hot dry weather. It is
also has the advantage of reducing weed growth. When the onions have
reached maturity, or the required size, watering should cease and the soil
around the bulb removed to allow the onion to ripen in the sun.

When the onion bulb has matured the foliage turns yellow and topples over.
At this point the onion should be left for about two weeks and carefully
lifted on a dry day using a garden fork. The onions harvested and not
required for immediate use must be dried either outside, or inside if the
weather is inclement. Drying takes about 7 to 21 days depending upon the
size of the onion and the drying conditions.

Prior to storage the onion should be inspected carefully and all damaged,
soft, spotted, or thin necked onions discarded, or used immediately in the
kitchen, or set aside for freezing. The ‘quality' onions can then be stored
when dried. It should be noted that some onion cultivars, particularly the
Japanese onion varieties, do not keep well and are thus unsuitable for
storing. Onions should be stored on trays, in net bags, in old stockings,
or as onion ropes in a cool well lit place. If these measures are taken the
onions will keep in good condition until late spring.

Salad onion varieties should be harvested when the bulbs are 0.5 to 1.0
inch in diameter, the harvesting season being between March and October.


Salad Onions

Although the thinnings of spring sown maincrop onions can be of use in
early summer salad varieties such as White Lisbon and Guardsman are grown
solely for salad use. Seeds sown thickly in drills during August, or March
are used when large enough from late spring onwards.


Other Allium species grown for culinary use


Shallots\ Eschallot

These are generally grown for pickling but they do have other culinary
uses. Rather like large onion sets they are planted in early March 9 inches
apart in rows 1 foot distant. After producing clumps of bulbs in July they
are lifted and the bulbs separated and dried.


Pickling Onions

These onions are grown specifically for pickling purposes There are two
main types:

1. Brown Pickler
2. Paris Silver Skin

These onions are grown from seed placed in drills 9 inches apart and 0.5
inches deep. The seed is sown quite thickly in drills during March. The
onions are lifted when the foliage withers.


Garlic - Allium sativum

Cloves of garlic are planted 6 inches apart and 1 inch deep in a sunny spot
between February and March. The crop is lifted when the foliage dies back.
The harvest can be stored as strings in a cool dry place.


Leeks - Allium porrum

Seed is sown in a seed bed between late March and early April. The crop
should be kept weed free and well watered in dry weather. The seedlings
should be transplanted 9 inches apart in late June.


Tree Onion - Allium cepa var viviporrum

The small bulbs should be planted 1 inch deep and 18 inches apart between
November and March. The developing tall stems will require support.
Clusters of small onions develop at various levels on the stem. They can be
harvested for use between August and March.


Welsh Onion - Allium fistulosum

Pieces taken from clumps of this onion can be planted at any time of the
year 12 to 18 inches apart. Clumps can be lifted in winter, or early spring
for use in salads and cooked dishes.


Potato Onion -Allium cepa var aggregatum

These onions are planted and cultivated in the same way as shallots.


Chives - Allium schaenoprasum

These are small bulbs which are often used to replace onions in salads,
stews, etc.. Often called a herb they can be raised from seed sown thickly
0.5 inches deep. They can also be propagated by splitting up clumps and
re-planting the offsets. They should be spaced 1 foot apart. The foliage
for kitchen use can be cut at any time between early May and October.







ALLIUM PROBLEMS


1. Roots, Bulbs and Stem Bases


Observation       Probable Cause

Eaten, Small maggots present    ONION FLY

Distorted or split - Bloated and distorted base  EELWORM

- Bulbs splitting   FAULTY GROWING CONDITIONS

Rotting  - Going soft at top of bulb  NECK ROT

- leeks rotting at soil level,
  Pink discolouration present  FOOT ROT

- Soft rot at sides with
  Blue\Green fungus   BLUE MOULD

- Soft, smelly rot mainly
  At sides    BACTERIAL ROT

- White mould present at
  Base     WHITE ROT


2. Plants


Observations       Probable Cause

Onions with thick necks     FAULTY GROWING CONDITIONS

Running to seed      BOLTING











3. Leaves


Observations       Probable Cause

Discoloured  - Bright orangy spots present  RUST

- Brown spotting with grey
  Mould coating on spring
  Onions    GREY MOULD

- Dark stripes under scales
  Bursting to reveal black
  Mss of spores   SMUT

- Dying from tips with fine 
  Downey, fungal covering  DOWNEY MILDEW

- Silvery streaking down the
  Leaves    THRIPS

- Tips of leek leaves becoming
  Water soaked then white and
  withering    WHITE TIP

- Yellow streaks on leaves of
   Shallots and onions   SHALLOT VIRUS YELLOWS


Eaten   - Onion and leek leaves holed
  And eaten    LEEK MOTH

Twisted       EELWORM

















PROBLEMS AND CONTROL


Bacterial Rot

A soft rot of onions occurring in storage as a result of attack by the
bacterium Erwina carotovora var carotovora and other related bacteria. The
attack results in the tissues becoming soft and foul smelling. Such attacks
usually follow physical damage during harvesting and storage.

Control

Onions should be dried off thoroughly after harvesting and handled very
carefully. If the onions are to be stored as ropes one should ensure that
the old leaves are thoroughly dried before tying them in. Store the onions
in a cool dry place taking time to examine them at regular intervals - i.e.
at least once every month - removing any bulbs that are showing any sign of
disease.

Blue Mould

This is a fungal disease caused by  Penicillium spp.. As with bacterial
rots, this condition usually follows physical damage during harvesting and
storage. Deseased bulbs develop round tufts of a blue-green fungus.

Control

The treatment is the same as that for bacterial rot.


Bolting

This term is used to describe the formation of a flowering stem which
inturn prevents the formation of an onion bulb, or a decent leek stem.
Bolting may be caused by a shortage of water, planting to early, or onion
sets being stored at an incorrect temperature before planting.

Control

Soil should be well prepared by incorporating plenty of organic matter to
help conserve moisture. The heads of flowering stems should be removed as
soon as they are seen - not in the case of chives where flowering is
normal. These onions should not be stored and used as soon as possible.


Downey Mildew

The causative organism Peronospora destructor attacks onions and shallots
and has also been found on tree onions. Attacks are worst in wet years, but
this disease can also be a problem in dry years in more humid districts. At
first pale spots appear on the foliage which becomes covered with a fine
felted fungal coating. Spores from this mass develop spreading the disease
further entering the soil where they can persist for four or more years.
Infected bulbs will rot in store.

Control

Onions should be grown onwell drained soil where there is a good
circulation of air. A three or four year crop rotation cycle should be
followed. Any deseased plants should be dug up and burned immediately they
are seen and the remaining unaffected plants sprayed with Mancozeb, or a
copper fungicide to protect against further attack by the organism. Where
the disease has been troublesome in previous years spray new crops as a
matter of routine before any disease is seen.

Eelworm

The onion eelworm Dytilenchus dipsaci is just one member of a very numerous
and widespread group of pests. They have been recorded as affecting over
400 different species of plants. On onions the pest causes the leaves of
the plant to become puckered and bloated. The bulbs may crack or split.
Once an attack is established very little further growth occurs. If the
attack occurs late in the season a bulb may be produced but it is likely to
split. If the bulb is placed into store it will be infective and the
eelworm will continue to breed and spread.

Control

Bulbs suspected of being infected with eelworm should not be stored. The
onion eelworm can attack many other vegetables, thus infected bulbs should
be dug up and burned immediately. Brassicas are not affected by onion
eelworm and so can be grown in areas affected by the onion eelworm. No
chemical controls presently exist.


Faulty Growing Conditions 

Planting to early can result in bolting, or running up to flower in the
first year instead of the second. This is also the case with dry
conditions. Heavy rain following a dry period can cause bulbs to split at
the base while over wet and lush conditions may result in ‘bull neck' a
condition where the onion produces a very thick neck with a poor storage
life.

Control

Control is achieved by thorough soil preparation before planting
incorporating organic matter into the soil to act as a water reservoir in
dry weather and as a sponge in wet weather. To avoid the development of
‘bull neck' do not over fertilise.


Foot Rot

Foot rot of leeks is due to attack by the organism Fusarium culmorum a
fungus which causes the outer leaves of the plant to rot at soil level. The
affected tissue has a pink, or red colouration. The rot may then progress
into the centre of the leek. The plants eventually wilt and die. The
condition is exacerbated in hot, warm weather.

Control

Foot rot is only usually a problem when leeks are grown in the same soil
year after year and so a three or four year crop rotation cycle should
prevent attacks. If an attack does occur remove and burn all affected
plants.


Grey Mould

The organism Botrytis cinerea attacks spring onions in wet winter weather.
Oval white spots often with a water soaked margin are found towards the
leaf tips. Other diseases may also be found in association including
Sclerotina botrytis squamosa and Sclerotina botrytis porri. In milder damp
weather the more typical grey, mouldy fungal growth appears on the spots.
Growth of the affected plants may become checked and they become
unappetising as a result of the damage.

Control

Spraying with sulphur, benomyl, or carbendizim is effective in controlling
grey mould.

Leek Moth

The Leek Moth Acrolepiopsis assectella feeds mainly on leeks, but onions,
shallots, and garlic can also be affected. Caterpillars mine into the
growing points of the plant and then eat into the folded leaves resulting
in a ‘shot-hole' effect when the leaves unfold. In the case of onions and
shallots the caterpillars feed within the hollow leaves. There are three
generations of this organism each year if conditions are favourable.

Control

Remove and burn old leaves and dead leaves on which the organisms may be
pupating. Deep digging and regular cultivation is also helpful by
disturbing, or killing the pupating stage. Treatment with a soil
insecticide may also prove helpful.


Neck Rot

Neck Rot is caused by Botrytis allii a fungus which attacks large bulb
onions as well as the pickling varieties. It sometimes causes considerable
losses in store. There is often no sign of the damage to come when the
bulbs are lifted, but a softening of the tissues around the neck of the
bulb becomes apparent two or three months later. A mass of hard, black
resting bodies of the fungus - known as sclerotia - can be found under the
bulb scales. The fungus moves vertically through the bulb until the rot is
complete. Leeks are largely immune from attack, but shallots and garlic
suffer the same fate.

Control

Infection may be present on the seed and so it is essential that new
‘clean' seed is purchased each year. Fungicide treated seed should be sown
if the disease has previously been a problem. Dusting the seed with benomyl
before planting is beneficial. As harvest time approaches do not cut off,
or forcibly bend over the tops of onions but let them die down naturally.
When lifting discard any bulbs with a softening of the neck, dry the
remaining bulbs thoroughly before storing. Follow a crop rotation to avoid
the spread of the fungus.


Onion Fly

The organism Delia antiqua attacks onions, leeks and shallots. The early
summer in most years is the worst time for damage. The adult - which looks
very much like the common house fly - lays its eggs in the late spring on
the leaves and necks of young plants, or in the soil near to the plants. In
a few days the maggots emerge and burrow into the plant to feed. In three
weeks the maggots are mature and are about 0.5 inches long. They then leave
the plant and pupate in the soil. Two generations of the fly are common in
one year, three generations occur in some years if the prevailing
conditions are favourable.

As the maggots bore through the plants scales they cause the leaves of the
plant to wilt. As many as thirty maggots can be found on a single plant.
Severe infestations result in the bulb rotting in the soil as the result of
a secondary infection. Some bulbs may not show signs of infestation until
they are cut, or they begin to rot in store.

Control

Treat the soil with chlorpyriphos, or diazinon, or pirimiphosmethyl
insecticides once the pest is spotted.


Rust

Leek Rust - Puccina allii - is primarily found on leeks, however onion,
chives, and garlic are also susceptible. Affected plants develop oval
pustules on their foliage, on which orange spots appear. Attacks of rust
appear quite serious, but there is little effect on yield. Attacks are
worst during wet weather.

Control

Good crop rotations will help control the disease by separating older,
possibly infected plants, from the younger seedlings. Applications of
sulphate of potash may reduce the incidence of attack. Where the disease
has been a problem in previous years spray with a copper, or mancozeb
fungicide.


Shallot Virus Yellows

This virus causes yellow streaking in the first leaves to appear from the
infected shallot bulb. Similar damage can also be seen on onions. The later
leaves are more yellow, crinkled, and sometimes flattened and the plants
may collapse. The disease is spread by aphids and so previously healthy
plants may become infected as the result of aphids feeding on the infected
plants. 

Control

Remove and burn all infected plants. Use good, clean onion sets purchased
from a reliable supplier.


Smut

The onion smut fungus Urocystis cepulae Is a seed and soil-bourne disease
which can have serious effects. It attacks both bulb and spring onions, and
leeks, shallots, chives, and garlic. Infection spreads through the plant
causing dark grey stripes to appear. These areas burst revealing masses of
black powdery spores which contaminate the soil for a number of years.
Legislation prevents the sale of contaminated plant material in Britain.

Control

Raise seedlings in a seed bed where the disease has not been a problem in
previous years. Burn all infected material immediately and follow a three,
or four year crop rotation cycle. There is presently no chemical control
available wich is suitable for garden use.


Thrips

The onion thrips Thrips tabaci can be seen on onions and leeks in large
numbers during humid weather. They are a small, thin, black insect - orange
in their larval stage - which puncture plant cells as they feed leaving
silvery streaks and stripes. Distortion and stunting of the plant results
from a severe attack. The pest is responsible for spreading the spotted
wilt virus.

Control

Spray with fatty acids, permethrin, or pyrethrins at the first signs of
silvering. Repeat the spraying if necessary.


White Rot

The fungus Sclerotium cepivorum is responsible for white rot. It attacks
all onions, leeks, garlic, and shallots. Affected plants develop a fluffy
white mould over the base of the plant resulting in the death of the roots
and leaves. Black resting bodies - called sclerotia - appear in the mould
which fall into the soil where they infect subsequent crops. Affected
plants usually rot due to secondary bacterial infections.

Control

Remove and burn any infected material together with some of the surrounding
soil. Raise plants in a proprietary seed compost and follow a three to four
year crop rotation cycle.


White Tip

This is a fungal disease caused by the organism Phytophthora porri. It is a
problem of leeks where the leaf tips become water-logged, die back, and
become pale and papery. Affected leaves rot down to soil level and growth
and yield are severely affected. Damage can be seen in late summer and
autumn.

Control

Collect and burn all infected material. Follow a three or four year crop
rotation. Spraying with a copper fungicide may protect plants from attack.




































ONION VARIETIES


Brown Skinned

Caribo
Rijnsberger - Balsyora
Hyton
Hygro
Rijnsberger - Robusta
Giant Fen Globe
Ailsa Craig
Showmaster
Bedfordshire Champion
Sturon
Jet Set
Unwins Exhibition
Reliance
Stuttgarter
Turbo

Red Skinned

Red Baron
Southport Red

White Skinned

Albion


Japanese/Autumn Sown Onions

Express yellow
Buffalo
Keepwell
Ima Early Yellow
Senshyu Semi-Globe Yellow
Radar

Salad Onions

White Lisbon
White Lisbon - Winter
Guardsman
Winter White Bunching
Savel
White Knight

Pickling Onions

Brown Pickler
Paris Silverskin

Garlic

Long Keeper

Leeks

King Richard
Tilina
Gennevilliers - Splendid
Franse Zomer - Pancho
SwissGiant - Albinstar
Autumn Giant - Argenta
Autumn Giant - Goliath
Winterreuzen
Blauwgroena Winter - Alaska
Autumn Mammoth - Verina
Musselburgh
Yates Empire
Giant Winter - Carina
Giant Winter - Wila
Walton Mammoth


I hope this is what you require.
Please forward your comments.

Brian
113223.2340@compuserve.com

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