CO-Horts Blog

Thursday, March 26, 2015

Onions Anyone?

Posted by Eric Hammond, Adams County

Last week we began planting the 2015 edition of the Northern Colorado Onion Variety Trials.  This project has been going on for over 40 years (the earliest report I can find from the trial is from 1971) and is an annual rite of passage in our office. 

 Each year seed companies submit onion varieties they would like trialed.   With the help of local farmers, volunteers and “onion biologists” (A position we created to be able to pay some of the people who help us) we plant and then evaluate them on several different characteristics.   The process and procedures of the trial provide an interesting glimpse into large scale agriculture that as gardeners most of us don’t  get to experience.


Having no formal training or experience in traditional agricultural production the first year I helped with the trial I was fascinated by the process of planting the onions.  The planter places single seeds at precisely 3.5 inch intervals at a depth of a half of an inch.  This means they expect, and normally archive  close to 100% germination.    As seedlings emerge we evaluate germination as "percent stand" (which is just code for percent germination).
Planting at Sakata Farms in the Spring of 2014

"Onion biologists" evaluating emergence
Teasing apart leaves to expose thrips which tend
to be found near their base
When mid-summer comes around we begin to evaluate the onions for their responses to pests.   The most taxing evaluation we do is an assessment of thrips populations.  Thrips are tiny insects which feed on the leaves of the onions (along with other plants).  They are one of the major pests of onions in the state.   There is some thought that onions which have leaves that are different shades of green or waxier will be less attractive to these insects.   There is also interest in finding varieties that tolerate thrips feeding, meaning that they produce an acceptable yield even when populations are high.  So, we crawl through the onion field on our hands and knees wearing magnifying glasses to count the number of thrips on individual onion plants.  This evaluation is my personal nemesis.  The first year I participated I apparently had a gap between my tee shirt and pants on my lower back.  By the time we were finished in the field I had managed to give myself a sunburn which had the color of a deep bruise (be thankful there is no picture).

Thrips on an onion leaf.  I wonder how many thrips I have eaten in my life?
Note our sweet magnifying headgear.

Counting thrips populations in Hudson

Iris yellow spot
Later in the summer we also evaluate the plants for the incidence and severity of iris yellow spot virus.   If the infection is severe enough, the virus can reduce yields.  Some varieties appear to have some tolerance or resistance to the virus.  Researchers and plant breeders would obviously like to identify such varieties.  So, we note the presence of the oval shaped lesions caused by the virus and rate their severity. 


In the fall, we harvest the onions and sort them to determine yield, size and the amount of doubles for each variety.  Most onions grown in Colorado are stored and used in applications which require a “medium” sized onion.  Larger sizes are desirable for specialty applications (has anyone has a “Bloomin’ Onion” recently?).  Double onions are not desirable for some uses such as onion rings.   Red onions are also evaluated for the quality of their color (which is a fancy way of saying they have their “redness” evaluated).

Harvesting onions last fall
My wife who I have coerced convinced to help
with the trial.  Where else can you learn how to juggle onions?

After yield and size have been evaluated the onions are bagged back up and placed in storage.  In January, we pull them out and evaluate how well they stored.   This can be a very slimy and smelly process for some of the varieties. 

Our retro onion sorter
Onions are evaluated after  storage for firmness and scale quality
Onions in January after storage
I can’t overstate how valuable the cooperation of local farms is in the trials.  Without the donation of space in their fields and storage facilities and time with their very valuable planting equipment and personnel, the trial could not exist in its current form.

So why do we put all this effort into this project?  Well, onions are a valuable and economically important crop in Colorado, nationally and worldwide.  Over 5,000 acres of onions were planted by Colorado farmers last year and our state’s harvest yielded an estimated 26 million pounds of onions.    This seems like a lot until you consider that globally something like 170 countries grow onions on approximately 9.2 million acres.  I guess the take home message is that the world is a big place and a lot of people living on it like to eat onions.  The Northern Colorado trial and other others like it are small but important pieces in contributing to the continued success of the crop.

No, the drone is not real


  1. From someone who has benefited from eating the onions (not raw of course), I can confidently say that the Adams County onion project is fantastic and so necessary for our onion growers. I just used up the last of the onions that you generously shared...looking forward to harvest 2015!

  2. This is so fascinating, and something that, even as gardeners, we don't even think about. Thank you so much !

  3. This comment has been removed by the author.

  4. What a cool project and great blog topic!! Fun to see you our there getting dirty too...!