Late frost - Sprouting trees

Julio-Rufo

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Dear forum,
My name is Julio, and I would like to say hello to everyone.

Let’s have a brief introduction first. For the past years I have developed my bonsai hobby in Spain. Something like 3 years ago I moved to Basel, Switzerland. Last autumn I decided to recap with the hobby here again, so I bought I few frees, mainly raw material (Acer palmatum “sin deshojo”, one Ulmus and one Picea).
As it was quite warm in the last weeks and the trees started to sprout I had to repot the Sin deshojo (like one week ago).

The trees are doing well, the Ulmus is really full of buds opening as well as the Sin deshojo. The Picea also has quite a lot of buds, but not ready to be repotted I would say.

Unfortunately the temperature will drop quite a lot in the following days, where temperatures of -2°C or -3°C (26-28 F) are expected at night for one week. Therefore I am a bit concerned about what to do with the trees. As they are in a terrace and I don’t have any greenhouse the only option would be to bring them inside during night. I assume even if the temperatures are low the Picea and it’s buds will do OK outside, right? So my concern is more about the recently repotted Acer Palmatum and the fresh buds and new growth of the Ulmus.

What do you think?

Thank you very much,

Julio
 

Shibui

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Recently repotted acer have no problem with similar temps here. It takes temps down around -5 to damage new emerging leaves and probably much lower again to hurt roots. Acer palmatum here have recovered after experiencing frost burn in the past so such is rarely fatal.
Predicted temps are for the open air. On your terrace, close to the house, actual temps should be a few deg or more higher owing to thermal mass and heat leakage from the house so probably closer to 0C would be my guess. Just moving the trees closer to the walls will make even more difference.
if you are really concerned the trees could be taken inside at night and returned out in the morning but I don't think that will be necessary given those temps
 

leatherback

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Keep them out of direct sun and wind when frozen. Besides that is it not really a problem for temperate species to get the odd night time frost on opening buds. Also when just repotted.
 

Cadillactaste

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I was raised in an era, to do the two step..I personally move my own trees into the protection of my cold greenhouse at night. That is just, what I was taught. If you search In the search engine...I'm not alone. I live lake front...my temps are always colder than forecast because of a microclimate. I also don't trust the forecast to be right on even figuring a ten degree difference...what happens if it's colder than predicted for others areas? Which always is the case here. Mine are tucked away...and I sleep well with no concern. That is just the way I prefer to do things. I know a few...who lost trees when the temps got colder than forecast. I am not willing to lay my trust in a weather person. But that is me. But I know I am not alone in doing the two step.
 

VAFisher

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Why risk it? Move them in.

Forecast here is 36F tonight which is too close for comfort for me with trees that have broken dormancy or have been re-potted. I spent 20 minutes moving them all into the garage a little while ago. No worries.
 

leatherback

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Why risk it? Move them in.
Soft keepers make weak trees?

Everybody has to do what they feel is best of course. If I loose a few leaves I do not really worry because I know my trees are healthy and will regrow them, maybe even get some more inner buds to pop. But trees get their frost hardiness by ever lower temperatures in fall, and frost hardiness is reduced by increasing temperatures in spring. Budding out is triggered by temperature and day length. To me, the more you mess with that the earlier your trees budd out and reduce their frost hardiness. So where one might protect for the night frost you see coming, you weaken the tree for the odd frost that you did not hear about.

We get frost again later this week, with a peak of -5c / 23F now in the books. My olives will return to the shed for that.
 

Cadillactaste

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Soft keepers make weak trees?

Everybody has to do what they feel is best of course. If I loose a few leaves I do not really worry because I know my trees are healthy and will regrow them, maybe even get some more inner buds to pop. But trees get their frost hardiness by ever lower temperatures in fall, and frost hardiness is reduced by increasing temperatures in spring. Budding out is triggered by temperature and day length. To me, the more you mess with that the earlier your trees budd out and reduce their frost hardiness. So where one might protect for the night frost you see coming, you weaken the tree for the odd frost that you did not hear about.

We get frost again later this week, with a peak of -5c / 23F now in the books. My olives will return to the shed for that.
Many of my trees see frost in fall... not spring. I know many who go that route. What you choose is great for you. I'm not willing to risk my trees to temps which maybe drop lower than forecast for spring. Which is very common where I live.
 
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