Why roses are red and violets are blue

Today I finished the chapter on vegetables in “What Einstein Told His Cook 2”. One of the tidbits that stuck with me was the fact that (red) roses and violets both have the same pigment; it’s an anthocyanin that, like litmus paper, responds to pH with a color indicator. Rose petals are slightly acidic, so the pigment shows up as red, while violets are slightly alkaline and therefore appear blue. (Gosh, I shouldn’t have bothered buying that 100-pack of pH indicator paper; I’ve got 11 rose bushes outside!)

Apparently, the presence of anthocyanin also explains why the new growth on a rosebush is tinted red, but the older leaves are green; new growth that hasn’t yet begun producing chlorophyll is vulnerable to radiation from the sun, so extra anthocyanin is produced in the meantime, which protects it from UV.

Now I’m wondering: if I take a violet petal and drop it in some vinegar, will it turn red? Can I dye my roses with household chemicals? My roses are actually white, so no telling what would happen in different pH conditions (maybe nothing; the white could mean that they lack anthocyanin). I hear an experiment begging to be performed this weekend…

Edit: I may have to wait on this; I forgot that I’d just pruned all of my rose bushes down into skeletal stumps of themselves, with no blooms to be had.

5 of 5 people learned something from this entry.

  1. jim said,

    February 7, 2007 at 3:25 pm

    (Learned something new!)

    Interesting question – would you do your experiment with slightly less acidic liquids like milk or soda?

  2. wkiri said,

    February 7, 2007 at 9:42 pm

    Sure! I’ll have to try a range. I can even use my pH indicator strips as a reference.

  3. Heuristics Inc. said,

    February 9, 2007 at 10:39 am

    (Learned something new!)

    So that’s why, huh? Interesting! Michelle also told me that some flowers will bloom in different colors based on the pH of the soil they’re planted in (hmm, don’t currently remember which ones), so I bet you could do an experiment like the ones kids do – put the flower in a solution of water & food coloring, but in this case use vinegar…

    By the way, Wil Wheaton posted this the other day and it made me think of you and specifically this journal:
    Thought you would like the idea of that book.

  4. wkiri said,

    February 11, 2007 at 12:02 pm

    (Learned something new!)

    Bill, you might be thinking of hydrangeas — they can vary from pink to purple to blue blooms, and (after looking it up) indeed this is also due to anthocyanin response (to the pH of the soil rather than the plant itself as with the roses).

    Also, thank you for the “Intellectual Devotional” recommendation via Wil Wheaton! It’s going on my to-read list right now!

  5. Heuristics Inc. said,

    February 12, 2007 at 10:20 am

    (Learned something new!)

    Yup, hydrangeas, I asked M this weekend. We have some now, so it’ll be fun to see what they come up as in the spring! Cool to see it’s the same mechanism. I really like the idea of that book too. Thought of you right away :)

  6. Iain said,

    February 13, 2007 at 10:09 pm

    (Learned something new!)

    Interestingly a friend of mine did something like that with Red Cabbage. Apparently by modifying the pH you can make it turn Blue. He also produced white somehow(?)… the idea was that for July 4th…..

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