Science Questions

Does unseasonable weather confuse plants?

Mon, 24th Oct 2011

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Sinead O'Dwyer asked:

Does unseasonable weather confuse plants?


Emily -   So that's a really good question.  I'veAutumnal Vineyard in Napa Valley been confused myself.  I went from flip-flops to winter coats and back again!

I think that itís even more important for the plants to know when winter is -  they can't just nip to the shops.  They have to have reserves for winter and know which season is coming so that they can prepare.  They do this by measuring day length so they can know that if you've got a lot of night time and not very much day, then you're in the middle of winter and of course, the other way around as well.  So if you've got a lot of sunlight and not very much night time, then itís in the middle of summer.  But you can imagine that spring and autumn would be a bit of a confusing area because the day length can be very similar. And itís very different in springtime,  you're waking up, you're sprouting, you're making flowers. Whereas in autumn, you've got to do the opposite Ė you've got to lay down reserves and get ready for winter.  So plants have a mechanism to deal with this called vernalization and itís where they require a prolonged cold period before they'll germinate or flower, and this will stop them making new flowers in autumn when they should be getting ready for the winter.  

Itís surprising how hardy and resistant most plants can be to extreme cold.  You can get willow trees that can tolerate liquid nitrogen - so minus 196įC - if they're prepared. You can't just dunk them in it.  They have to have time to make cryoprotectants, and also, anti-freeze proteins. 

But then, they're able to deal with it very, very well.  So, I would say that yes, the plants will have been a little bit confused.  You might have seen some roses resprouting and the buds they've made will die, but most of them are able to judge the day length, and actually deal with it very well.

Chris -   I've got a spring plant in my garden that should flower in April and itís come back into flower again.  Presumably because we had that cold snap a little while ago and it now thinks, ďHey!  Weíve had winter and now itís time for spring again.Ē

Emily -   Most of them require a bit of a longer period of cold than that, but yeah, itís probably thinking, ďIíll give it a goĒ and if the buds die then the buds die.

Chris -   That must be bad for the plant though because presumably, itís eating into reserves itís built up over the summer that are now going to be used to sustain it over the winter, and they won't be there.

Emily -   Itís not ideal, you're right but itís not the end of the world.  So the plant will have enough reserves normally.  It can store them in tubers and that sort of thing.


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