Comparing yield of female asparagus and male asparagus plants

Asparagus (Asparagus officinalis) is a perennial vegetable that is dioecious, meaning that individual asparagus plants are either male or female (or sometimes they are 'super male', but that is a topic for another day). There aren't a huge number of dioecios vegetables, which makes asparagus interesting.

With asparagus you want many long and fat dense spears that are not fibrous, when they start to become thinner you stop harvesting for the year. It is common advice to remove/kill all female plants as the males are said to provide larger yields of fatter, longer, and better quality spears. It is common advice that female asparagus produce thin spears so can be weeded out early.

But is this really true? I have never met anyone who has tested this theory, have you?

 

I have always wondered if this was true or just another garden myth that people spread about. I used to have heaps of seed grown green asparagus plants scattered through our orchards, some produced fatter or longer spears than others. I never noticed any difference between the males and females.  But these grew from seeds deposited by birds, and were various ages, and none of them were watered or weeded, so you can't really draw any sensible conclusions from that.

I also had a female purple asparagus plant that used to grow the fattest and most succulent spears I have ever seen. Perhaps that is a variety trait and male plants of the same variety would be even better? 

I wanted to do a comparison to see if this is the case, but I lack the necessary resources to run a trial properly. As I could not run this trial to get this information myself I looked up some peer reviewed papers, and the results were really surprising.

Female asparagus producing long fat straight spears

Firstly there were a bunch of papers claiming that certain all male F1 cultivars (or 'male dominated' F1 cultivars) out yield traditional heirloom varieties that have both male and female plants. That is nice, and useful information for commercial production. This wasn't surprising, many F1 vegetable hybrids out yield tastier heirloom varieties. I want to compare the yield and quality of male to female of the same variety, not just comparing one variety to another. I am also interested in quality, not just quantity.

I found a few papers published in 1909 saying that all male asparagus fields provide higher yields than mixed fields. After reading though the methods it sounds like the mixed fields had issues with competition (from seedlings) rather than being a direct comparison between male asparagus and female asparagus plants. Again this is useful for commercial growers, but not all that useful for home growers with small numbers of plants.

Purple asparagus

So I kept looking and I stumbled across a bunch of papers, some published recently and others were far older than I am, and they compared male to female asparagus plants of the same variety to one another. Some papers focused on just one variety, others focused on multiple varieties, and they all had similar trends.

I will provide the full abstract of one of these papers, and then use sentences from others to highlight the findings.

 

Comparison of spear yield and quality between male and female asparagus plants in protected mother fern culture (https://www.ishs.org/ishs-article/1223_24)

"A higher yield of spears is generally obtained from male asparagus plants than females in outdoor culture. However, recently in Japan, it was reported that the spear weight and yield of female plants was generally greater than those of males in rootstock-planting forcing or mother fern culture. 'UC157' plants were grown in large black polyethylene pots. Spears were harvested daily and their weight and external appearance were recorded for four and two years, respectively. Spear numbers were not significantly different between male and female plants in spring, and tended to be greater per male plant than per female plant from summer to autumn. Mean spear weights per female plant were significantly higher than those per male plant in spring and from summer to autumn. Spear yields per female plant were also significantly higher than those per male plant during spring, whereas no significant differences were found from summer to autumn. Spearhead tightness, an important external quality indicator, was significantly better in female plants than males. From these results, we concluded that in spring, the spear yield and quality of female plants would be better than those of male plants without causing a difference in the annual yield. Therefore, a choice of all-male varieties seems to be not necessary and all female cultivation could be profitable for protected mother fern culture in Japan, since the price of spears in spring and heavier spears is higher in the Japanese asparagus market".

 

A large scale experiment which compared male and female asparagus plants from several varieties published in 2016 said: 
"The results of this study show that the female plants had a significantly higher rootstock weight, weight per spear per plant, and weight per early spear per plant, whereas the male plants had a significantly higher total spear number per plant, early spear number per plant, and significantly fewer days to first harvest".

Another paper said: 
“With the average stalk diameter there was no difference between male and female plants in 1964; in the first two years the diameter of the female plants was larger than that of the male”.

Yet another paper stated: 
“Female plants had higher stalks and longer length to primary branch than male plants”.

Another paper states: 
“…highest number of very thick spears appears generally in female plants”.

 

This is all incredibly interesting, it means that female asparagus plants do not necessarily produce fewer spears in spring (when I am harvesting them), or thinner spears, or spears of lower quality than male asparagus plants. 

If anything these papers demonstrate that female asparagus plants often produce fatter, longer, better quality spears while males tend to produce more spears that are shorter, thinner, and of poorer quality.

Female asparagus producing berries

Knowing this, the first thing you do is ask why we have always been told to remove and kill all female asparagus plants.

 

I believe this advice is mostly due to female asparagus’ incompatibility with large scale commercial production, and partly due to the extra work required to look after them for home gardeners long term. 

Male asparagus plants flower and then the flower falls off, female asparagus plants flower and produce little red fruits that are filled with seeds. In time the female asparagus plants drop their fruit, the seeds eventually germinate and the bed gets choked with too many plants, leading to a reduction in quantity and quality of yield. Sometimes birds eat the berries and deposit the seeds in concentrated places causing a bit of a weed issue.

For a commercial grower with acres of asparagus this would be devastating and costly/difficult to overcome. Spraying a pre-emergent herbicide to prevent seedlings from growing sounds like extra time and money being spent, growing only male plants would be better in this situation. 

In a commercial scale, producing many thin spears often results in higher profits than growing fatter, longer, higher quality spears. Remember that people in cities need to eat, and commercial agriculture must focus on profits and feeding landless people. If they didn't we would have massive famines in the city. Commercial agriculture must focus on producing large quantities of food that people can afford, often this is done at the expense of quality.

Commercial asparagus growers tend to want thin spears. I have even seen certain asparagus varieties described as having thick spears, and then recommending planting closer than normal so they will produce thinner spears.

When growing food in the back yard can focus on quality.  Quantity is nice, but when home grown it comes second to producing high quality food.

Asparagus surviving the heat and dry

For a home grower with a small number of plants who is growing for personal consumption rather than profit, this news is not so gloomy. In the long term they either need to remove all the berries, or carefully dig up and transplant the seedlings, otherwise the bed gets choked and only thin spears are produced. On the other hand, as a home grower with few plants it isn’t too hard to pull the berries off and sow them somewhere, providing you with extra asparagus plants to either keep or give away. So this extra work actually becomes a positive. 

According to the literature above, female plants often produce longer, fatter spears of higher quality. These are exactly the traits that I want when growing asparagus!

If you are growing food at home you may as well grow the best. I am not growing asparagus to sell the spears, I am growing to eat them. So if the choice I have to make is either more spears that are thin and low quality, or less spears if they are fatter and of superior quality, I will choose the latter every time.

Asparagus growing between QLD arrowroot

Personally my plants are all seed grown and I just grow whatever. I have a mix of male plants and female plants and I normally remove the berries. 

 

I have grown asparagus from seed, it takes a lot of time and effort so most people prefer to buy dormant crowns. I have been reluctant to sell seed grown asparagus as (unless I grew an "all male" F1 hybrid) a mix of male and female would be produced and I wasn’t sure if the female plants were worth it. I certainly don’t want to sell low quality plants. 

Now that I know more about the quality of female asparagus plants, and why we are told to remove female asparagus plants, I plan to get some seeds of a few heirloom varieties to grow them out and offer year old crowns for sale.  

Keep an eye on my for sale page from next winter and I will try to have a few crowns of heirloom asparagus varieties for sale.