Agriculture Reference
In-Depth Information
Onions
AMARYLLIDACEAE
Alliaceae was once considered to be a taxonomic family in and of itself; now it is ranked as a
subfamily of the Amaryllidaceae. Crop plants of this Allioideae subfamily are still known
colloquially as onion family plants or alliums (after the genus
Allium
). Onions, leeks, and
garlic are mainstays of most home gardens. Their pungent, spicy flavor lends an unmistak-
able flair to many vegetable and meat dishes. The strong aroma of onions and garlic comes
from allyl sulfide compounds in the leaves and bulb.
Botanically speaking, onions are made up of a tightly clinched basal rosette, which sup-
ports leaves, called scales, which act as thick storage organs. The bulb is an underground
storage organ in onions, garlic bulbs, and shallots, an above-ground reproductive organ in
other alliums like topsetting onions and the scapes of garlic.
GENERAL PROPAGATION CHARACTERISTICS
Allium flowers are perfect but self-infertile. Individuals
are located in an umbel-like, spherical cluster and open over the course of about 30 days, with most
opening during the second week. Anthers of individual flowers emit pollen for three days before the fe-
male flower organs are able to receive pollen, which prevents self-pollination.
Many alliums are grown as ornamentals, for their beautiful buds and flowers. These flowers catch the
eye of not only gardeners but also a wide variety of insects. Bees, wasps, and hoverflies are the most
important pollinators of alliums; the wind, on the other hand, hardly plays a role. In commercial seed
production, isolation distances of at least 1 mile (1.5 km) are used. In diverse home gardens, 500-650 ft.
(150-200 m) should suffice, meaning that growing more than one variety of the same species in one
garden per year is likely not possible, unless mechanical isolation or hand pollination is used.
This is no ornamental onion: the flowers of the cultivated leek are also a thing of beauty.
Many alliums produce no seeds and are propagated vegetatively. Garlic and topsetting onions, for ex-
ample, produce bulbils instead of flowers; they do produce flowers when under stress, but these are usu-
