Long Day Sweet varieties will generally mature a few weeks before the storage
varieties. They will store for one to five months, so eat them fresh
from the field. These varieties will do well from the mid-west to the
Short Day Sweet varieties start the bulbing process when the day-length reaches
10-12 hours. Since they are planted primarily in the south during the
winter or early spring months they will take approximately 110 days
until they mature. If planted in northern states in late spring, they
will mature in just 75 days but produce smaller bulbs. The earlier you
plant them, the larger they will get.
PREPARING THE SOIL & PLANTING
Onions are best grown in direct sunlight on raised beds at least 4″
high and 20″ wide. It is best to add 1-2″ of compost to the soil and
mix in well. Spacing of rows should be 36″ from the center of one row
to the center of the next row.
Set plants out approximately 1″ deep with 4″ spacing. On the raised
bed, set two rows on each bed, 4″ in from the side of the row. Should
you want to harvest some of the onions during the growing season as
green onions, you may plant the plants as close as 2″ apart. Pull every
other onion during the growing season, leaving some to mature into
After planting add organic fertilizer approximately every 4 weeks
during the growing season. General Purpose or Vegetable type fertilizer
is fine but make sure the numbers are low such as 3-2-1 or 6-3-2. You
can also add Osmocote once when you plant which will slow release
during the entire season.
Water the transplants immediately after planting. Because of the
shallow root system, onions require frequent furrow irrigation. Avoid
overhead irrigation, which causes foliage diseases. If the foliage has
an unhealthy, yellowish tint the plants are being over-irrigated. The
soil will be overly dry around an under-watered crop and may become
cracked. Onions generally require 30″ of irrigation during a growing
season and the closer to harvest, the greater the need for water. If
the onion does not get enough water it will not make a large bulb. When
the necks start falling over and the onions mature, watering should be
discontinued and the soil allowed to dry.
DISEASES AND WEEDS
Orienting plant rows and spacing to maximize air movement helps reduce
the time that leaves are wet and results in less disease.
Weed control is very important early in the onion growing process. Be
careful not to damage the onion bulbs when cultivating. Keep soil loose
so onions can expand easily but do not push dirt on top of the onions
since this will prevent the onion from forming its natural bulb. A
light organic mulch will help control weeds and preserve moisture; pull
the dirt back from bulbs when they begin to bulb.
HARVEST AND STORAGE
Onion tops turn yellow and fall over when the growing process is
complete. Bending the tops over early will only expedite the process
and decrease bulb size. Pull the onions out of the ground and let them
dry in the sun for two days. Lay the tops of one row of bulbs over the
bulbs of another to prevent sunscald. When onions are dry, clip roots
and cut back tops to one inch or braid uncut tops together and hang
onions in an airy spot.