Monday, May 7, 2018

Tips on Growing Onions

Onions are an ancient crop.  They have both medicinal and culinary uses.  For the cook they are essential.  Dried, raw, or cooked they are versatile and indispensable in so many dishes.  They are easy to grow and a great storage crop.

The formation of the onion bulb is dependent on day length.  When browsing the catalogs you when notice that onion varieties are classified according to the photoperiod or day length required for that particular variety to bulb up.  They grow vegetatively or develop top green growth until the required number of daylight hours is reached and then the bulb begins to swell and grow.

Short Day Varieties require 10-12 hours of daylight and do well in Southern regions.  They can be grown in the North but do not get very large.

Long Day Varieties require 14-16 hours of daylight and do well in Northern regions

Day Neutral of Intermediate Varieties start bulking with 12-14 daylight hours.  These can be grown with success anywhere.

If you are north of the Oklahoma/Kansas border or 36 degrees latitude plant long day or day nuetral varieties. If south of that plant short day or day neutral varieties.

Onions interplanted with Merlot lettuce.


Onions require a sandy loam soil amended with plenty of organic matter and a dry organic fertilizer incorporated shallowly into the soil before planting.  They have shallow roots and need to have plenty of water to do well near field capacity. Even moisture is the key. the bulb is not part of the roots but a swollen stem. The roots extend from the base of the bulb and are very shallow. Onion seed has low germination rates and should be replaced every two years.

Onions interplanted with cauliflower.

Planting Options

You have different options when it comes to growing onions.  They can be started from seed, planted as sets, or transplant plants.  All of which can be purchased from the nursery or garden catalogs.

I have the best result using seed. You need a good 5 months to grow from seed.   I start them indoors from Feb 1st - mid February and plant them out in April.  I direct seed green onion or scallions in April.  The seedlings can be transplanted in the garden 4-6 weeks before the last frost when they are about 2-3 inches tall.  They like cool weather for top growth and warm weather to  produce  the bulb.

Onion sets are immature bulbs grown the previous season.  They are usually labeled only by color:  red, yellow, or white.  Bulbs that are the size of a dime produce the best bulbs.  Anything larger may go to seed before producing decent sized bulbs.  Bulbs smaller than a dime can be used are green onions or scallions.

Onion transplants.  Those the size of a pencil do the best.  Smaller ones can be used are green onions.

You can also purchase onion transplants.  They are seedlings grown the previous year.  They are dormant when you receive them and will look dry.  Soak the roots in a little water and plant about 1 inch deep.  This will cover the roots and not bury the neck too deeply.  This is a good option if you do not want to grow your own transplants.

You can fertilize with fish emulsion but once they start to bulb up do not fertilize.  Top growth will stop when the plant focuses its energy on developing a bulb.

Plant  in rows or use the square foot method.  Scallions can be 2" apart or 16/square foot.  Larger onions need to be about 3-4 inches apart or 9/square foot.  Be sure to mulch around onions it helps to hold moisture in the soil.

Ok so I don't take many pictures of the under appreciated onion, but they are one crop I use the most in cooking and canning. They probably deserve more attention when I have the camera out. 

Types of Onions

Scallions or Green Onions:  
Most onions can be pulled when young and used as green onions.  There are specific bunching onions grown specifically for green onions.  There are both green and purple varieties.  Pickling onions are also available.

Sweet Onions 

Sweet onions are not astringent or as sharp as other onions.  They are sweet and frequently used raw.  They do not store well. Walls Walla and Vivaldi are wonderful sweet onions. Sweet onions do not store well.  Plan on using them first.

Multiplier Onion or Potato Onions:
These are similar in growing patterns to garlic.  They are planted in the fall with the tip of the onion even with the soil level.  They send up leaves the following spring.  Remove any seed heads that develop.  They produce a cluster of bulbs from the one bulb that you plant.  Harvest in July or August just like garlic and cure.  Save some bulbs for next years planting.

Walking Onions or Egyptian Onions

These are fun to grow.  They form small bulbs underground and a cluster of bulbets on the seed head instead of a flower.  You can harvest and cook the underground bulbs and replant the bulbets on the top of the stalk.  If you leave them unharvested the top of the plant tips over or "walks" on the ground and reroots itself.


Shallots are a small, mild allium prized by chefs.  The are elongated with reddish skins.  When peeled they separate into cloves like garlic.

Onions citing under a porch.

Storage Onions

This is the onion most are familiar with. There are red, yellow, and white storage onions. Each varies in its storage length but generally if stored properly they can last from 3-6 months.

Yellow onions are consider to be an all purpose onion.  They are used most often in cooking with a good balance of flavor.  They become sweeter the longer they cook.  Spanish onions are a sweet yellow onion.

White Onions are more pungent.  They are more tender and have a thinner pappery skin.  They are used just like yellow onions.

Red Onions are similar to yellow but milder.  They are used raw in salads and salsas.  When cooked the color fades.  If they seem too strong raw, then soak slices in water ahead of time.

Onions interplanted with broccoli and celery.


You can harvest an onion at any stage.  If you want large bulbs then wait for the tops to turn yellow.  Bend the tops over with a rake and leave for a week.  This will direct more energy to maturing the bulb.  When leaves turn brown pull the onions.  Do not wash the onion just brush off the dirt.  Cure them in the shade with good air circulation for 7-10 days.  This allows the papery skin to dry and provide protection during storage.  When they are done curing brush off the loose soil, clip the tops down to 1 inch and trim the roots.  Those with thin necks will store the longest so use the thicker necked onions first.


Most onions store for 3-6 month at 32-45 degrees with 65-70% humidity.  If you don't have a root cellar a vegetable bin  in the refrigerator will work.  They will not last as long at room temperature. Check your storage onions frequently and remove those that sprout or are rotting.

Onions are a good companion crop with lettuce, cole crops and carrots.

Diseases and Pests

Onions are generally disease and pest free.  They are considered pest deterrents when planted among lettuce, cole crops, and carrots.

Thrips can be a problem.  They  are visible with a hand lens. They have elongated bodies and large dark eyes.  They cause silvery lesions on the leaves.  They suck plant juices and can cause deformed bulbs.  Neem or pyrethrin is effective on thrips.

Leeks have similar cultivation requirements.

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