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I still like my arugula, kale and some lettuce varieties after they are bolting. A friend told me that those plants produce toxins when they bolt in order to ward off insects, and that we should never eat them. Does anyone know about the truth of this?

user4650
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    Logically, kale (a brassica) after bolting shouldn't have toxins, because there are several bolted brassicas known as non-toxic, such as broccoli. As for lettuce, some people grow it for the stem (bolted) and call it celtuce. I don't know about arugula. I have eaten many bolted vegetables, and as of yet have had zero health issues, of any kind. I don't have any scientific evidence to back this up. After a few quick searches, I've found several sites stating that bolted vegetables sometimes contain toxins, but they did not mention what toxin, or the concentration of it. Also no references added – J. Musser Jun 17 '14 at 18:33
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    Most "toxin" claims are nebulous with no backup. Seems some confuse the stronger flavors in matured plant matter with "toxin". Provide toxin names, studies, exact plant names and I'll start to believe it's not an old wive's tale. Note: we're talking about something different from things like Rhubarb which has high oxalic acid content in the leaves and a much lesser quantity in the stems which allows them to be eaten. – Fiasco Labs Jun 17 '14 at 19:02
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    I agree with both the other comments - I suspect that people who think bolted vegetables are toxic are confusing 'toxic' with 'inedible', but bolted veg are only inedible because of taste, for most become more and more bitter. – Bamboo Jun 20 '14 at 09:15

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I believe the "toxins" referred to by your friend are the bitter components that you will often find, especially in leafy plants, once they begin to go to seed (which is known as bolting.) In the linked article, there is mention of the specific compounds that cause the bitter taste, "sesquiterpene lactones" and some speculation that the bitterness conveys at least some insect resistance. I was able to confirm that there are, indeed, studies online which look into this, so there is probably some evidence that providing protection for the next generation of seeds is at least one of the reasons for the increase in bitterness of greens as they mature. Collards, kale, cabbages, arugula, turnips, spinach and especially lettuce are all well-known for becoming less palatable as they begin to gear up to produce their seeds.

TeresaMcgH
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Never heard of toxins being produced by bolting plants. Looked this up and really...you shouldn't worry. Vegetables 'bolting' get more bitter, pithy and thus less edible. This is caused (by popular opinion) by cold-snaps. Nothing you can do to stop bolting once the plant has been 'alerted' that its environmental conditions show an unpredictable pattern and the plant responds by using desperate measures to ensure it makes babies...seed. A few seeds are better than none.

These plants are gambling! They are immediately assessing risk versus success. No emotion, it is just their 'job' in life. Instead of enjoying the confidence of perfect conditions where the plant is allowed to get as big as it can before it needs to start procreating, one signal, showing the environment can't be trusted...and the plant throws the switch for 'making seeds'...All their energy goes into making seed. Leaves aren't sweet because they had to get that energy to the seed-making and leaves just have to make-do...

This is tough, not being scientific. I am just trying to help to understand plants using terminology from us animals. Just remember that plants are totally alien to us animals.

If you can remember where you got this information and are able to reconnect, please do so. Let us know where this information is from...! Thanks!

stormy
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    There's nothing wrong with being scientific. In fact, iit's encouraged. – J. Musser Jun 22 '14 at 02:01
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    "This is caused ... by cold-snaps." It's also caused by heat and drought down here in the south. Basically anything that makes the plant think it could die soon. – Philip Jun 22 '14 at 03:05