Common Name: Potato Onion

General Information

Allium cepa aggregatum is a herbaceous, perennial plant producing a cluster of leaves around 30cm long and a flowering scape around 50cm tall from an underground bulb. The plant divides, forming in time a cluster of plants[].
Both the shallot and the tree onion are included here. The shallot is still widely cultivated, in gardens and commercially, for its bulbs, whilst the potato onion is little known.

Known Hazards

There have been cases of poisoning caused by the consumption, in large quantities and by some mammals, of this plant. Dogs seem to be particularly susceptible[].

Botanical References

Range

Not known in wild

Habitat

Not known in wild.

Properties

Edibility Rating
Medicinal Rating
Other Uses Rating
Habit	Bulb
Height	0.40 m
Pollinators	Bees, Insects
Cultivation Status	Cultivated

Cultivation Details

Allium cepa aggregatum (the shallot) is a commonly grown vegetable, mainly in the temperate zone but it also succeeds in many areas of the tropics.
Prefers a sunny sheltered position in a light well-drained fertile soil[] but tolerates most soils. Does not grow well on heavy clays[]. Prefers a pH in the range 6 to 7[]. Tolerates a pH in the range 4.5 to 8.3.
The shallot is a genuinely perennial form of Allium cepa that is widely grown in temperate and tropical areas for its edible bulbs[]. These are milder but smaller than the onion. There are several named forms[]. The plant is easier to grow than onions, matures faster and keeps better[], though yields are lower.
The potato onion was at one time fairly widely grown as a vegetable, but it has now fallen into virtual disuse[]. The bulb grows deeper in the soilthan the shallot, and divides to produce a number of underground bulbs each year in much the same way as shallots (which grow nearer the surface). Large bulbs divide to form 5 - 15 bulbs whilst smaller bulbs grow into one large bulb[]. There are some named forms available[].
According to one report, the bulbs should be planted fairly deeply[], whilst another report says that they should be planted just below soil level[].
Plants are very tolerant of high temperatures up to 30°c and bulbing only occurs at temperatures above 20°c[]. Plants rarely produce viable seed in temperate areas, they are usually propagated by means of their bulbs, each one dividing up in the growing season to produce from 2 to more than 12 new bulbs[].
Bulbs can become infected with virus, it is important to only plant clean stock[].
Onions are closely related to Allium oschanini. O.Fedsch., a wild species found in C. Asia[].

Edible Uses

Bulb - raw or cooked[, ]. A nice onion flavour, when chopped up finely they make a nice addition to salads and can also be used as a cooked vegetable or as a flavouring in cooked foods[, , , , ]. Some of the cultivars are considered to be gourmet onions[]. The bulbs can be up to 6cm in diameter.

Leaves - raw or cooked. A pleasant, mild to strong onion flavour, though they should not be harvested in quantity since this would reduce production of the bulbs[].

Flowers - raw. Used as a garnish on salads. The flowers are somewhat dry and are less pleasant than many other species[].

Medicinal

Although rarely used specifically as a medicinal herb, the onion has a wide range of beneficial actions on the body and when eaten (especially raw) on a regular basis will promote the general health of the body.
The bulb is anthelmintic, anti-inflammatory, antiseptic, antispasmodic, carminative, diuretic, expectorant, febrifuge, hypoglycaemic, hypotensive, lithontripic, stomachic and tonic[, , ]. When used regularly in the diet it offsets tendencies towards angina, arteriosclerosis and heart attack[]. It is also useful in preventing oral infection and tooth decay[]. Baked onions can be used as a poultice to remove pus from sores[].

Fresh onion juice is a very useful first aid treatment for bee and wasp stings, bites, grazes or fungal skin complaints[, ]. When warmed the juice can be dropped into the ear to treat earache[]. It also aids the formation of scar tissue on wounds, thus speeding up the healing process, and has been used as a cosmetic to remove freckles[].

Agroforestry Uses:

Allium species usually grow well with most plants, especially roses, carrots, beet and chamomile, but they inhibit the growth of legumes[, , ]. They are, in general, bad companions for alfalfa - each species negatively affecting the other[].
Members of this genus are rarely if ever troubled by browsing deer[].

Other Uses

The juice of the plant is used as a moth repellent and can also be rubbed onto the skin to repel insects[].

The plant juice can be used as a rust preventative on metals and as a polish for copper and glass[].

A yellow-brown dye is obtained from the skins of the bulbs[, ].

Onion juice rubbed into the skin is said to promote the growth of hair and to be a remedy for baldness[]. It is also used as a cosmetic to get rid of freckles[].

The growing plant is said to repel insects and moles[]. A spray made by pouring enough boiling water to cover 1kg of chopped unpeeled onions is said to increase the resistance of other plants to diseases and parasites[].

Propagation

Seed - sow spring in a cold frame. Seed is seldom produced by this plant[].
Division in late summer. Harvest the bulbs as the foliage dies down and store them in a cool place. In areas with mild winters the bulbs are traditionally replanted on the shortest day of the year, but in colder areas it is best to wait until late winter or even early spring[]. Plant the bulbs only just below the soil surface[].

Plant out bulbs in late winter or very early spring. Plant firmly to half the bulbs depth and protect from birds until the bulbs have rooted[]. (Birds seem to have a fascination for pulling the bulbs out of the ground and then leaving them lying on the surface[].) Traditionally, bulbs were planted on the shortest day and harvested on the longest. Smaller bulbs are less likely to bolt as a result of exposure to cold conditions[].