Why Do Plants Bolt?

Some of my Kale plants look like this…

And they should really look more like this…

Why? because they’ve bolted (or run to seed). Running to seed is when the plant flowers and produces seed prematurely. The reason most planst run to seed is either increasingly warm weather (Lettuce doesn’t like hot weather) or increased light levels (sometimes Spinach, Cabbage and Kales will bolt in early Spring). A few plants will also run to seed if they are short on water and they become stressed (Rocket, or Arugula as it’s called in the States).

One thing is certain; once a plants starts to bolt there’s no stopping it. Lettuce and the like will become inedible. Anyone who has ever eaten a leaf from a bolting lettuce will tell you – it ain’t nice. While the flavour of Spinach and Kale will remain largely unchanged, so you can strip the plant and then compost it.

What I can’t understand (and help me out here if you know why) is that some of my Kale plants have bolted and others haven’t. I’ve treated them the same way, watered them at the same time and they even came from the same seed packet.

Is it really just pot luck? Still, the flowers are pretty and I think I’ll leave the plant in the ground for now – if only for it’s decorative value.

23 Comments on “Why Do Plants Bolt?

  1. I’m still trying to figure out bolting too….. I am worried about my lettuces with the 80*+ temps here the last few days and the strong sunshine. Last fall the kale also bolted in a last burst of heat from the weather – it was very pretty after though, a deep purple over the folded in plant among the “blooms”.

  2. Just in case the tendency to bolt early is genetic it might be better not to save the seed.

  3. The chances are that the ones that haven’t bolted yet, will. Sorry to be the bearer of bad news, but this happened to me last year and I thought ‘oh well, at least it’s not all of them’. But it was in the end!

  4. My rhubarb has bolted, and I wondered yesterday if it would be good to eat … any ideas?


  5. What are the temperatures doing in your area? Did it just suddenly get warmer?

  6. Joanna, with rhubarb you should keep picking the flower buds off to stop it bolting. I don’t know if it is safe to eat, or good for the plant to eat it, when that happens..

    Gill, it’s just possible that kale flowers naturally at that stage and needs it’s flower buds pinching out, too, but I have no experience of growing kale. Down here it hasn’t rained that much overall this Spring, so could your kale have been shorter of water than you think?

  7. May be you are experiencing effects of the global warming …
    To avoid bolting I usually look for specific varieties that are just slow to run to seed.
    These are some that worked out pretty good last year: spinach america that I grow in spring and lettuce canasta that’s the only lettuce I’m able to grow in summer.

  8. If these kale plants were from seed sown last season then they are just doing what comes naturally. They aren’t perennial – at least they have to reproduce at some point ! So kale, chard, etc planted last summer/autumn which has stood the winter feels it’s the new year and is just doing the next stage of what it does. Kale ( is it Tuscan ? ) is best sown as seed late spring early summer and picked and eaten late autumn through winter and if you are lucky into early spring then it’ll flower. Same as sprouting broccoli if you think about it. Leave those new broccoli shoots unpicked and you’ll get flowers.

  9. Leafy vegetables such as lettuce, kale, coriander in particular, rocket, all bolt for 3 reasons.
    1. They require large amounts of fertilizer, in particular, high nitrogen fertilizer such as chicken manure, or worm farm juice. Cow is pretty good too.
    2. They require lots of water. They become stressed and think their time is up, so they start to flower and set seed. Water the soil well and apply a mulch such as straw,shredded newspaper or lucerne. Throw on a few handfuls of blood and bone, and these mulches will become fertilizer. High fibre mulches such as shredded newspaper and straw take a long time to breakdown, and can leach the soil of nitrogen, so add the blood and bone, and the soil will be wonderful.
    3. Lettuce in particular, don’t like hot sun. Plant them under other plants such as fruit trees, or in the shadows of a fence so they don’t get afternoon sun, behind structures such as a seat. Coriander is similar, but not as needy. Also, coriander comes in 2 varieties, and if you plant the coriander seed from the Indian spice shop, they will go to seed instead of producing lots of leaves. Plant these from seed packets.

  10. why did the plant bolt? Sounds like the beginning of a joke.. like “why did the chicken cross the road?”

    Surely its because it is getting ready to flower!

    My rhubarb is doing its best to send up lovely fat flower buds, but this cruel human keeps chopping them off again!

    I love your blog.. keep it up :-)


  11. I have one side of the garden that does not get any sun really it has a few fruit trees and not much else

    Do you think I could grow lettuce along there or would it be too shady

    Also thanks for the comments re rhubarb i never knew it could bolt and I just thought I had some sort of mutant growing as it looks well strange

    love this blog

    Just wondering where you get the time to run your own business,look after Jackson, write the blog and grow all the veg

    I don’t seem to be able to find the time to get anything done except the planning stage


  12. My sprouting broccoli, that went in last autumn, still has no buds on it

    Do you think I should just leave it in or would it have done something if it was going to by now

    I thought it was an early veg but my mother in law keeps telling me it is a summer veg


  13. Well from my readings and experience bolting is mostly caused by temperature.
    If you have a patch of ground for instance that gets intense sun and raises the soil temperature and other areas get a bit less direct soil heating, where the soil temp gets too high (don’t know specifics sorry) that’s where your problem starts, on seed packets there are optimum germination temp ranges if the seed is constantly in excess of it’s top range it will bolt.
    If the soil is too rich in nutrients and or poorly prepared ie, with air pockets due to poor digging that will not help, the trouble is also too much shade can cause bolting where the seedling is desperate to find light and expends all it’s energy growing to the light.
    I have found that it can be a bit random as well so all I can say is that Mother Earth doesn’t let us have it all our own way all of the time…. thankfully ;-)

  14. Bolting is a natural process, it’s the survival mechanism in a plant. If the weather get to be above where the plant will survive, it will try to produce the next generation (seeds) as quickly as possible.
    If you catch a plant in the very early stages of bolting, you can temporarily reverse the process of bolting by snipping off the flowers and flower buds. In many plants, such as broccoli and lettuce, this step only allows you some extra time to harvest the crop before it becomes inedible.

  15. It’s not all bad news. My curly kale has bolted, but the flower shoots look and taste almost exactly the same as those on purple sprouting broccoli. A few bonus meals in there.

  16. I just reead about this, and as far as I remember cabbage plants bolt when they get cold. I’ll check with the book if you want me too, it’s a good one. But I think it might be frost.

  17. I have just stumbled accross your gardening blog and find the content absolutely fantastic. I have learnt a great deal about gardening from this blog. Keep up the good work please over the summer months. I will be reading with interest

  18. When spinach bolts how long do I leave the stems? They are growing like a vine and I was wondering if I should just cut it down or wait for it to die……I’m new at this! I live in southern California and the temp is about 100 right now…..I’ve gotten many salads out of this plant already……I think it’s spent!

  19. Hi there,

    When rocket bolts is it finished ? If I trip it back to the soil will it grow again next year ? Or should I just pull it up and throw it away?

    Any help would be great as this is our first year growing fruit n veg.

    Thanks in advance !

  20. Why do some bolt when others don’t, all else being equal? That argues for genetic variability. Some will bolt early, some will bolt late, most will be in-between, but all will bolt when changing temperature and water conditions indicate that the best chances for that individual to reproduce are now rather than later.

    Under natural selection in a warming world, the earlier bolter might be more successful in sending its genes into the future, whereas the late bolters might die before they have a chance to flower and produce seeds. That’s under natural conditions, with no extra water, fertilizer, or protection from predator bugs.

    Under garden conditions, the late bolter is “better”, but it might not be able to survive on its own.

  21. Ok. So it’s hot enough that my spinach bolted. Can I grow another batch now or wait until late August? It sometimes snows in September. Zone 4. Thank you.