Does unseasonable weather confuse plants?

24 October 2011

Question

Does unseasonable weather confuse plants?

Answer

Emily - So that's a really good question. I've been confused myself. I went from flip-flops to winter coats and back again! I think that it's 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 it's 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 it's 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 - you've got to lay down reserves and get ready for winter. So plants have a mechanism to deal with this called vernalization and it's 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.

It's surprising how hardy and resistant most plants can be to extreme cold. You can get willow trees that can tolerate liquid nitrogen - so minus 196Ã?,°C - 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 it's come back into flower again. Presumably because we had that cold snap a little while ago and it now thinks, "Hey! We've had winter and now it's time for spring again."

Emily - Most of them require a bit of a longer period of cold than that, but yeah, it's probably thinking, "I'll give it a go" and if the buds die then the buds die.

Chris - That must be bad for the plant though because presumably, it's eating into reserves it's 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 - It's not ideal, you're right but it's 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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