The Secret of Red Rhubarb…


“i bought canada red rhubarb and instead i got the same old junk i could dig up anywhere.  it has turned green and has no red at all. -P.”

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As I often like to do when educating others on horticulture…

… it’s time to blow a myth all to pieces!

Myth:  Rhubarb loses its red color because the plant gets old and genetics deteriorate.  Or you weren’t given a Crimson Red/Canada Red/etc. variety.

Before I dispell this myth, I do want to note that there is always the possiblity that the above is true.  You could have the incorrect plant.  Or, if your plant is old, it could be that you haven’t divided your rhubarb recently and the discoloration of the stems is based on stress from having too much in one spot.

However, if you know you bought the right thing and you regularly divide your plants…

Fact:  Rhubarb doesn’t like acidity and it doesn’t like shade.

As a kid growing up, I remember listening to my Grandmother and my Mom talk about one of my Great Aunt’s rhubarb patch.  All had gotten the rhubarb from the same relative and it was an old heirloom red variety.  Grandma’s and Mom’s was nice and red, but said Great Aunt’s was not.  Of course, the donating relative must have given Great Aunt some junk that “wasn’t true”.

When I was taking my graduate world vegetable crops class, I finally figured out why this occured.  (Who ever would have thought that perusing the Journal of Food Science for information on Lycopene production in tomatoes would make one run across it!)

First of all, rhubarb (Rheum rhaponticum) is rather pH-sensitive.   Rhubarb prefers to be grown in full sun with a soil pH of 6.0 to 6.8.

The number one reason why customers have problems producing red rhubarb is because the soil pH is incorrect.  But you say, “my soil pH falls in the above range.”  True, the soil in your garden does.  But the soil right around your rhubarb is not!

Why?  The tissues of rhubarb are acidic.  At the end of the season, as your rhubarb begins to die down for the season, each piece of plant material that falls to the ground carries the acidity with it.  Over time, the acidity from the tissue that is composted into the soil decreases the pH of the surrounding soil.  The red coloring leaves the plant and you end up with green stems.  If you rip out your old plants and plant new red stemmed ones right back into the same place, you are going to have more green stems.

So why does the plant do this?  A deep red petiole is the more popular among consumers, but these plants are often accompanied by poor growth and yield. Green varieties are often much more productive. Consumers also often assume the red stemmed rhubarb is sweeter than other colors but color and sweetness are not necessarily related. The Victoria variety, which is probably the greenest variety, can produce some very sweet stems.

The above photo shows study in which rhubarb was planted and allowed to grow in its own decaying plant material.  The top stem is first season growth and the stems increase in years to the bottom, which is fifth year growth.

In order to maintain the redness of your rhubarb, make sure you clean up the dying foliage from it each fall.  Cut the stems off as they begin to die back or thoroughly rake the area after all the plant material has died back.

 

 

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© Mertie Mae Botanics LLC and Horticulture Talk!, 2012. Unauthorized use and/or duplication of this material without express and written permission from this blog’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to Mertie Mae Botanics LLC and Horticulture Talk! with appropriate and specific direction to the original content.

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2 thoughts on “The Secret of Red Rhubarb…

  1. Pingback: Rhubarb fertlizer

  2. I am a small commercial rhubarb grower in North Ferrisburgh, Vermont. You are correct about the PH link to color, but as with everything to do with agriculture, it is a little more complex. I have one rhubarb bed where the color and stem quality were not so good. All plants in all beds are genetically identical clones. The PH was a little high due to some biochar and wood ash added at planting. When I acidified the soil a bit, both stem quality (fewer cracked stems) and color improved. The stem quality was a boron deficiency exacerbated by sandy loam soils and neutral ph. The compounds that produce red color require adequate available iron. That is a more complex equation than just PH, but a critical requirement for a deep red color, within genetic parameters, of course. PH plays a role in iron availability, and it did improve for me, by lowering the PH, but there are other factors at play. I am still working on that! Perhaps not surprisingly, the previously stressed plants also attracted more rhubarb curculio. In summary, PH range and adequate available iron and boron are critical to rhubarb. Thanks for your good work!

    Regards,

    David Booth

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