Chilling Hours for Oaks

[Teeder]

I have some potted oaks that I'm attempting to over-winter. Currently, they're in my basement which is about 55 degrees. My concern is chilling hours. Am I going to have problems getting them to wake up? I'd put them back out, but i worry about the roots freezing. Which is worse?

 

[RGrizzzz]

I have some potted oaks that I'm attempting to over-winter. Currently, they're in my basement which is about 55 degrees. My concern is chilling hours. Am I going to have problems getting them to wake up? I'd put them back out, but i worry about the roots freezing. Which is worse?

I keep mine in my garage. It gets cold, but not below freezing. I left a bucket with water in it last year, and I never saw ice. My oaks did well, but 50% of my chestnuts died back. I only have 5 chestnuts this year and the pots are bigger with older trees.

To answer your question, a hard freeze in a pot is worse. It could kill the seedling.

 

[Hoytvectrix]

I have some potted oaks that I'm attempting to over-winter. Currently, they're in my basement which is about 55 degrees. My concern is chilling hours. Am I going to have problems getting them to wake up? I'd put them back out, but i worry about the roots freezing. Which is worse?

You have probably seen this before, but Penn State has a page on this:

Make Like a Tree and Chill

ecosystems.psu.edu

Within that link there is another for accumulated chill hours: https://mrcc.purdue.edu/VIP/indexChillHours2

Based on this reading, I would think you would need to have them cooler for 1000-1500 chill hours for the buds to be fully dormant. It looks like Chill hours are counted when temps are between 35-45F. I would wait until the end of February (or when temps below 0 are less likely) and then set them outdoors to accumulate some chill hours. You could also just manually set them out when you have a week or two of cooler temps and then bring them back in if there is a cold snap?

I looked up on google scholar and I couldn't find any studies with oaks or related species that would be similar to what your seedlings have experienced. There was one paper that had holm oak. Here is a link to the abstract as well as a link to the research paper (I am not sure if this will work for you). They used a greenhouse that was around the same temps as your basement and it looks like they tolerated being taken outdoors. I think you are spot on about the risk of roots freezing and your climate might be different.

I have had terrible luck trying to overwinter oaks in containers, and have tried almost everything - insulated cool spot like your basement, uninsulated garage, insulated garage, buried and mulched outdoors, and fully exposed. The uninsulated garage here in MN seems to be the best so far. I wish I had better experience but I would love to hear how yours turn out based on what you try to do.

 

[RGrizzzz]

You have probably seen this before, but Penn State has a page on this:

Make Like a Tree and Chill

ecosystems.psu.edu

Within that link there is another for accumulated chill hours: https://mrcc.purdue.edu/VIP/indexChillHours2

Based on this reading, I would think you would need to have them cooler for 1000-1500 chill hours for the buds to be fully dormant. It looks like Chill hours are counted when temps are between 35-45F. I would wait until the end of February (or when temps below 0 are less likely) and then set them outdoors to accumulate some chill hours. You could also just manually set them out when you have a week or two of cooler temps and then bring them back in if there is a cold snap?

I looked up on google scholar and I couldn't find any studies with oaks or related species that would be similar to what your seedlings have experienced. There was one paper that had holm oak. Here is a link to the abstract as well as a link to the research paper (I am not sure if this will work for you). They used a greenhouse that was around the same temps as your basement and it looks like they tolerated being taken outdoors. I think you are spot on about the risk of roots freezing and your climate might be different.

I have had terrible luck trying to overwinter oaks in containers, and have tried almost everything - insulated cool spot like your basement, uninsulated garage, insulated garage, buried and mulched outdoors, and fully exposed. The uninsulated garage here in MN seems to be the best so far. I wish I had better experience but I would love to hear how yours turn out based on what you try to do.

Are you keeping them watered/damp?

 

[Teeder]

Thanks guys!
Water in my pole barn and garage freezes.
I may try moving them out and bring them back in it the temps drop too much.