Introduction and description
The ‘potato onion’ - Allium cepa aggregatum - 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.
According to Plants for a Future, it is "closely related to A. oschanini. O.Fedsch., a wild species found in C. Asia".
The plant is easier to grow than onions, matures faster and keeps better, though yields are lower. 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.
It is remarkably easy to grow, keeps better than almost any other variety of onion, and is ideal for the home gardener with restricted space. It was very popular in the past, but--like many old varieties--it has been passed over in favour of types more suitable for mechanical harvesting and mass marketing.
It is generally planted from bulbs, not from seed. Most sources say it should be planted in the autumn, but this probably applies only to areas with moderate climates. It can be planted in the spring as early as the ground can be worked and produces well when so planted, up to at least the most northern limits of planting zone 5.
"Sources differ about planting depth, some saying shallow planting is appropriate and others calling for deeper planting. This onion does tend to grow very close to the surface and a planting hole perhaps an inch deeper than the diameter of the bulb seems to work well. The onions vary in size from half an inch to three inches in diameter (1 - 8cm)."
More details will be provided later.