Japanese Maples Chill Hour Requirements

[Scrogdor]

In 9B we are around 50s average lows in the winter. All the JPMs here go through dormancy.

Dormancy also had to do with light, water etc. it’s a bunch of things.

 

[Maiden69]

My circle of Florida bonsai peeps...can't grow them. Interesting.

I'm late on this reply, but I think this has to do with the location. My first year with JM's in 2020 all my maples had severe scorched leaves, including my in-ground trident. Between 2021-22 the canopy and mass of my trident and yoshino cherry provide shade for my only 2 surviving JM's till last month and they barely get the edge of their leaves burn now. I think it is a combination of excess sun/heat/wind that kills them in hotter zones.

This year I placed a 50% shade cloth like @Clicio does, they did extremely well to the point that I decided to order 2 more cultivars. Next year I will have a zone just for JM's that will include the 50% shade at the beginning of summer till autumn, and a wind breaker (trying to find something that looks nice, if I can't I will probably use some sort of lattice boards since we get very strong winds at random times through the year.

 

[Cadillactaste]

I'm late on this reply, but I think this has to do with the location. My first year with JM's in 2020 all my maples had severe scorched leaves, including my in-ground trident. Between 2021-22 the canopy and mass of my trident and yoshino cherry provide shade for my only 2 surviving JM's till last month and they barely get the edge of their leaves burn now. I think it is a combination of excess sun/heat/wind that kills them in hotter zones.

This year I placed a 50% shade cloth like @Clicio does, they did extremely well to the point that I decided to order 2 more cultivars. Next year I will have a zone just for JM's that will include the 50% shade at the beginning of summer till autumn, and a wind breaker (trying to find something that looks nice, if I can't I will probably use some sort of lattice boards since we get very strong winds at random times through the year.

Oh my one maple came from Texas. Yeah foliage looked like crap by end of season for him... and it was in a greenhouse if I'm recalling correctly.

So your foliage looks ratty? Or not so bad?

But many southern Florida peeps won't battle with JM. Their words...zone envy.

 

[Maiden69]

This was before the shade cloth, dappled shade. 2022


This year 2023, it was under the full canopy of the trident and the cherry, I added the shade about 1 week before this pictures.




I'll see if I can grab a few more when I get home today.

 

[Maiden69]

Here are some pics from now. Not the best, my iPhone pics are not the greatest.





Some burned tips



The ones that are damaged more look like this, but this was with almost 70 days of 100 degree weather and no rain. I did ensure they where watered enough.

 

[Gustavo Martins]

You're in the Azores? What are your Winter temps like? There's still plenty of chill accumulation between 7.5C and 10C and your temps rise to no more than maybe 20C in the Winter. That's way different from a Florida zone 10 where it drops into the 0-5C range once or twice per Winter and then it is back to 18C night to 27-30C days. Winter heat will cancel our most chill. Here in the mountains in Hawaii in a zone 11b/12a the Japanese maples leaf out in July and lose their leaves in December-January.

Yes I'm in the Azores. My lowest temp ever recorded at sea level is 6C. My winters are very mild, no major daily swings in temperature. It stays around 10-12C most of the winter. Coldest month is March. My deciduous trees drop leaves mostly in January. Maples tend to leaf out in March. Others can take a bit longer April-May. At the moment, lots of trees are still pushing new growth now that we are past summer and temperatures are a bit cooler.

 

[Cadillactaste]

Here are some pics from now. Not the best, my iPhone pics are not the greatest.

View attachment 513871

View attachment 513872

Some burned tips

View attachment 513873

The ones that are damaged more look like this, but this was with almost 70 days of 100 degree weather and no rain. I did ensure they where watered enough.

View attachment 513874

I don't use a shade cloth...but I do understand the purpose for them. Nice safe on that foliage from last season.

 

[Deep Sea Diver]

If the tree is placed in a greenhouse, open the door when the temperatures get at/about 50F. Coupled with the mandatory greenhouse fan, it will serve you well. We do this to good effect in both greenhouses.

Chill hour requirements are complex and both species and cultivar dependent.

While researching chill hour requirements for the resource Over Wintering Bonsai Guide…

https://www.bonsainut.com/resources/overwintering-bonsai-–-theory-planning-and-case-studies-azalea-focus.49/

…there was a deep dive into the tree chill hour requirement models, species and cultivar requirements etc on and off for a couple months.

My take home (in general) is trees begin to accumulate daily chill hours when the temperature goes below 50F

… at a partial amount at higher temperatures near 50F … then gaining full ‘credit’ at 45-42F depending on the species. Then stopping accumulation below 32F.

Also in general, trees acclimate to a specific climate. Older trees tend to be much less resilient than younger trees. Especially more sensitive species.

Cheers

DSD sends

 

[Maiden69]

I don't use a shade cloth...but I do understand the purpose for them. Nice safe on that foliage from last season.

Thanks, shade cloth is the only way to deal with JMs and other heat (sun) sensitive trees in zones 8 and higher. Most JMs can be grown in full sun above that, with some exceptions. Think about it as your indoor setting for your tropicals. I can leave mine out almost all year long, except for the days that the temps will drop below 40. I think the longest I have kept them indoors has been 2 maybe almost 3 months and that was because I didn't want to deal with the shuffle.

@Deep Sea Diver there has been a few occasions that I had to scratch my head when it comes to chill hours. Mostly for fruiting trees that can be grown in the tropics like pomegranates. I was on a website looking at a few to buy and I noticed that they stated that without X amount of chill hours, the yield was going to suffer. Yet they fruit profusely in Puerto Rico on a Zone 12/13 area. Since then I just look at what other people close to me are growing and go from there.

 

[Deep Sea Diver]

@Deep Sea Diver there has been a few occasions that I had to scratch my head when it comes to chill hours. Mostly for fruiting trees that can be grown in the tropics like pomegranates. I was on a website looking at a few to buy and I noticed that they stated that without X amount of chill hours, the yield was going to suffer. Yet they fruit profusely in Puerto Rico on a Zone 12/13 area. Since then I just look at what other people close to me are growing and go from there.

It is true fruit trees suffer if they do not meet the chill hours requirements. As do bonsai trees.

Yet what that requirement depends on is the cultivar. There is also an acclimation factor.

So yes buy locally is the best best as the horticulturists have specifically bred the fruit tree for your climate…. Similar in some respects to using native trees for bonsai

Cheers
DSD sends

 

[Leo in N E Illinois]

A little off topic, but related to @Maiden69 comment about Pomegranates. The native range for Pomegranate is Mediterranean, not tropical.

I live in an area far too cold in winter to grow pomegranate, but for 42 years I kept a pomegranate growing. When I grew it as a tropical, protecting it from lows below say about 45 F, bringing it in with the orchids. It would flower with a scattering of flowers and fruit all year round. Usually only one or two flowers at a time, off and on all year round.

When I grew my pomegranate as a sub-tropical, allowing it to get several frosts to about 25 F or -4 C, then bringing it into a 35 to 40 F well house for remainder of winter, this method resulted in profuse flowering in spring, simultaneous fruit set, and then relatively few flowers later in the year. Overall, I liked the vigorous burst of growth in spring, but still had issues, no matter how close to freezing the well house was, the pomegranate would always break dormancy well before our normal last frost date, which meant the first few weeks of growth had to happen either under lights., which resulted in elongated growth that later had to be pruned back off or an "in and out dance" which this fat old man found increasingly difficult as my waistline grew and my hair turned white. I did find out that 19 F is lethal to pomegranates. I forgot one night in autumn, the tree ended up toast.

So pomegranate work very well, and are probably most productive fruit wise when grown as a sub-tropical. But they can be grown as a tropical, with no winter rest and they will produce flowers and fruit with reasonable predictability.

 

[Clicio]

Update on some of the maples under 50% shade cloth all year round, in Brazil.

Kotohime.


Kiyohime.


Orange Dream.


BUT!...

One of the Palmatum is showing signs of Chlorosis.
It's a relatively new one, still in the nursery soil. It will be repotted as soon as possible, after our scorching summer heat, IF the temperatures drop down a little in the Fall.

 

[xray]

Hey,
Do you think there is a limit for how many hours JM will be in dormancy/chill hours?
If about 1000 is the minimum and winter came early to my garden. Roughly estimated my JM will not be sleeping for about 4000 hours here in zone 5a.
Sounds like my maples will be bursting with energy come spring right?

 

[Deep Sea Diver]

Hey,
Do you think there is a limit for how many hours JM will be in dormancy/chill hours?
If about 1000 is the minimum and winter came early to my garden. Roughly estimated my JM will not be sleeping for about 4000 hours here in zone 5a. Sounds like my maples will be bursting with energy come spring right?

Trees do not gain energy during dormancy. Once the chill hour requirement has been met, the tree will wait for the temperature and/or daylight hour signals to bud.

Cheers
DSD sends