Alliums, which include many important vegetable crops, reproduce through cross-pollination and require isolation of varieties when grown for seed production. They include onions, garlic, leeks, and other species. Seed producers must isolate varieties of the same species by certain distances or through caging/bagging to prevent cross-pollination. Many alliums are biennials requiring vernalization and grow best from bulbs. Seeds should be harvested when dry and processed by threshing, screening, and drying to remove chaff while maintaining viability.

1. Allium Seed Production
Introduction:
Allium spp.are members of the family Amaryllidaceae. This genus consists of over 400
species including: ampeloprasum (leek), cepa (common onion), fistulosum (bunching
onion), sativum (garlic), schoenoprasum (common chives), and tuberosum (garlic
chives).
Pollination:
Alliums have perfect flowers but, can not self-pollinate because the male anthers shed
pollen before the female stigma is receptive. Therefore they cross-pollinate via insects
(flies and bees) or by manually pollinating (hand-pollinating) the flowers in a controlled
environment. Seed producers must keep in mind that varieties of the same species will
cross-pollinate with other varieties of the same species. Chives reproduce by division of
bulbs and produces seed. To reproduce garlic you must save healthy heads and replant
the individual cloves separately. Topsetting or hardneck varieties of garlic will produce a
seedhead with bubils. These can be planted, but it will take several successive years to
get good-sized heads.
Seed Production:
Many alliums (A. cepa) are grown out as biennials (taking 2 seasons to produce seed),
and require a cold treatment (vernalization) in order to flower. It is easiest to grow for
seed from bulbs rather than from seeds. Allium seeds are generally short-lived and should
be used in 1 or 2 seasons. When planting alliums (or any cross pollinating crops) for seed,
care must be taken to isolate same species varieties from one another, either through
mechanical isolation (caging, bagging) or by distance isolation. In addition to isolating
same species varieties, care must also be taken to preserve as much genetic diversity as
possible by planting a minimum number of plants. Listed to the right are ESTIMATES
for isolation distances and minimum population sizes. These values can vary greatly
depending on what you read and who you believe.
Species Isolation Distance Minimum Population Size
Leek 200 ft – 1 mile At least 50
Onion 1500 ft – 1 mile At least 100
Garlic 25 ft 10 cloves
Chive 1500 ft – 1 mile At least 100
Harvesting for Seed:
You should harvest your seed as soon
as the seed heads are dry, if you wait too long, the seed heads will shatter and you will
loose all the seed you spent the last 2 seasons growing out! Seed heads can dry in the
field if you plan on harvesting several times or be cut and laid out to dry if drying in the

2. field isn't possible. Keep in mind that drying seed in temperatures greater than 94° F will
damage the seed and if the drying seed head becomes wet by rain or watering, it will also
damage the seed.
Seed Processing:
Most allium seed heads (leeks and onions) need to be threshed first (we use a belt
thresher but this can be done by hand threshing) and then the smaller chaff can be
separated by using screens (see table to the right) or an air column or simply by
winnowing. I have also tried pouring the seed in a bucket of water. The light, unviable
seed and chaff will float and the viable seed will sink. You can either skim off the top
with a sieve or decant the unviable seed and chaff. Immediately after you get rid of the
chaff, you want to put the "good" seed into a mesh bag or lay it out on a screen to dry.
Crop Upper Screen Lower Screen
Onion 8 or 9 1/15 or 1/14
Suggested screen sizes for use with the Clipper Office Tester or hand screens).
ATTRA - Organic Allium Production: this link will provide you with some general
information concerning organic treatments used in onion production. The links given
below will provide detailed information on the diseases and treatments.
Crop Common Diseases Info/Treatment/Pics
Garlic ( A. sativum) Basal Rot, Blue Mold, Leaf
Blight, Neck Rot (Gray
Mold), Nematode (stem and
bulb), Punky Bulb, Rust,
White Rot, Purple Blotch,
Downy Mildew, Botrytis
Leaf Spot, Pink Root,
Garlic Powdery Mildew.
Oregon State University
Extension
University of Arizona
Extension
Onion (A. cepa) Basal Rot, Black Mold,
Botrytis Leaf Spot, Bulb
Rots, Downy Mildew,
Fusarium Bulb Rot, Iris
Yellow Spot, Neck Rot and
Bulb Rot, Stubby Root,
Pink Root, Purple Blotch,
Rust, Smut, White Rot
Oregon State University
Extension
University of Arizona
Extension