Horticulture/Allium

Allium is the genus which includes both Onions and Garlics, with about 1250 species, making it one of the largest plant genera in the world. They are perennial bulbous plants that produce chemical compounds that give them a characteristic onion or garlic taste and odor, and many are used as food plants. Allium is classified in family Alliaceae although some classifications have included it in the lily family (Liliaceae).

Members of the genus include many valued vegetables such as onions, shallots, leeks and herbs such as garlic and chives. A strong "oniony" odor is characteristic of the whole genus, but not all members are equally flavorful.

Description
Allium species occur in temperate climates of the northern hemisphere, except for a few species occurring in Chile (as Allium juncifolium), Brazil (Allium sellovianum) or tropical Africa (Allium spathaceum). They can vary in height between 5 cm and 150 cm. The flowers form an umbel at the top of a leafless stalk. The bulbs vary in size between species, from very small (around 2–3 mm in diameter) to rather big (8–10 cm). Some species (such as Welsh onion, A. fistulosum) develop thickened leaf-bases rather than forming bulbs as such.

Most bulbous alliums increase by forming little bulbs or "offsets" around the old one, as well as by seed. Several species can form many bulbils (tiny bulbs) in the flowerhead; in the so-called "tree onion" (A. cepa Proliferum Group) the bulbils are few, but large enough to be used for pickling.

Species
Some important species: ../Allium acuminatum/ - tapertip onion ../Allium ampeloprasum/
 * A. a. var. ampeloprasum - elephant garlic
 * A. a. var. kurrat - kurrat
 * A. a. var. porrum - leek (vegetable)|leek

../Allium anceps/ - twinleaf onion ../Allium angulosum/ - mouse garlic ../Allium atrorubens/ - dark red onion ../Allium campanulatum/ - dusky onion ../Allium canadense/ - Canadian garlic ../Allium cepa/ - garden onion ../Allium fistulosum/ - Welsh onion ../Allium neapolitanum/ - white garlic ../Allium nevii/ - Nevius' garlic ../Allium nigrum/ - black garlic ../Allium oleraceum/ - field garlic ../Allium oschaninii/ - shallot ../Allium ramosum/ - wild Chinese chives ../Allium sativum/ - cultivated garlic ../Allium schoenoprasum/ - chives ../Allium scorodoprasum/ - Sand leek ../Allium triquetrum/ - three-cornered leek, triquetous garlic ../Allium tuberosum/ - Chinese chives ../Allium ursinum/ - wild garlic, ramsons ../Allium vineale/ - crow garlic See full list.

Uses
Some Allium species, including A. cristophii and A. giganteum, are used as border plants for their flowers, and their "architectural" qualities. Several hybrids have been bred, or selected, with rich purple flowers. Allium hollandicum 'Purple Sensation' is one of the most popular and has been given an Award of Garden Merit (H4). By contrast, other species (such as the invasive Allium triquetrum) can become troublesome garden weeds.

Pests and diseases
../Leaf Spots/

../Downy Mildew/

../Southern Blight/

../Bulb Rots/ ../Rusts/
 * Onion White Rot: ../Sclerotinium cepivorum/
 * Onion Neck Rot: ../Botrytis alii/

../Smuts/

../Nematodes/ ../Aphids/ ../Thrips/ ../Flies/ ../Beetles/ ../Caterpillars/ ../Mites/
 * Onion Nematode
 * Shallot Aphid: ../Myzus ascalonicus/
 * Tobacco Thrips: ../Frankliniella fusca/
 * Western Flower Thrips: ../Frankliniella occidentalis/
 * Onion Thrips: ../Thrips tabaci/
 * American Serpentine Leafminer: ../Liriomyza trifolii/
 * Onion Bulb Fly: ../Emerus strigatus/
 * Onion Maggot: ../Delia antiqua/
 * Pea Leafminer: ../Liriomyza huidobrensis/
 * Seedcorn Maggot: ../Delia platura/
 * Banded Cucumber Beetle: ../Diabrotica balteata/
 * Beet Armyworm: ../Spodoptera exigua/
 * Saltmarsh Caterpillar: ../Estigmene acrea/
 * Bulb Mite: ../Rhizoglyphus echinopus/

Cabbage Moth, Common Swift moth (recorded on garlic), Garden Dart moth, Large Yellow Underwing moth, Nutmeg moth, Setaceous Hebrew Character moth, Turnip Moth and Schinia rosea, a moth which feeds exclusively on Allium spp.