Hello,
I have recently acquired Cedrus atlantica ‘Glauca’, but like always I may have not done enough research as to the climatic suitability of my house (Brisbane, Australia). The tree was procured from a Melbourne nursery.
We get the mildest of winters, and folks on a local bonsai forum have not had success is keeping Blue Cedars alive (though a friend that lives within a mile of me has a giant Himalayan Cedar in the ground and another old specimen in a pot).
People throw terms around like heat stress, but reading the Mirai guide, it sounds like they can handle heat alright. What are these trees doing in winter that is facilitated by cold temperatures? Is there some action I could take nutritionally as an alternative to the winter shitdown . Or is there a possibility that the local failures have been because of misdiagnosed tip blight (we are very humid until we are very dry).
Or should I start trying to sell the tree to someone in Toowoomba, the local temperate city?
So many possibilities. Looking forward to insight from the community. Cheers
I’m in Southern California and I think we have a similar climate. I have a ponderosa pine that might be in a similar situation as your cedar. I have only had it over 1 winter and not sure if we will get cool enough to give it the yearly chill hours for it to “rest”. I don’t think it’s the heat, but lack of down time and the relatively continuous growth all year that leads to the demise of these species in certain climates. I think I remember it usually takes about 3-5 seasons with a health decline over that time.
I’m sure others will chime in, but from watching the videos and hearing Ryan answer questions over the years of videos, this is what I’ve gathered as a problem with lack of winter dormancy.
I have been keeping in mind to potentially board my Pondo with someone in a more favorable winter climate. But I’m not sure if it would be worth keeping a species that would be a steep uphill climb in my climate.
They need a set amount of dormancy hours or it will die from carbohydrate exhaustion. You should be able to find the hour requirements for each species pretty easily. I know some folks in the Mirai community have tried keeping them in a refrigeration set up ( humidity is in issue)but it’s not clear if this is a long term or realistic solution.
I get the ‘they grow themselves to death’ concept… But why? My Chinese elms can just push and push and push… what is the physiological difference between species that do and don’t need the dormancy.
And if it’s carbohydrate expenditure, outside of temperature and daylight hours, could the withholding or application of certain nutrients convince these tree to relax for a bit?
Or there’s Hagedorn’s Heresy book, suggesting day/night temperature differential being more impactful… So many variables.
The selection pressures and adaptive strategies that evolved based on what survived to the next generation of trees.
Your comparison is not 1:1
Atlas cedar are native on mountainsides at 1,370 to 2,200 m (4,490 to 7,220 ft).
At 5k+ feet I could imagine that in the middle of the winter most of the trees needles are covered in snow. So it would be more advantageous to go dormant since the opportunity to photosynthesize is minimal.
The evergreens that did not go into dormancy did not get enough of their seeds into the generation and the ones that used “dormancy” did and outcompeted the other strategy. I am not saying this is “true” but this is a simple standard evolutionary selection hypothesis model that gives a possible why.
Comparing a broadleaf semi evergreen to true evergreen is like comparing a penguin to a seagull.
The structure of the “solar panels” photosynthetic material is very different. Needles vs leaves.
The absence of leaves improves wind transmission of pollen for wind-pollinated plants and increases the visibility of the flowers to insects in insect-pollinated plants.
In the northern hemisphere leaf drop is driven by daylight length and air temperature (winter) in warmer subtropical climates leaf drop is typically in the “dry season” so I could speculate it is potentially driven by “rainfall amount” as one of a few signals
This isn’t the best answer but to be fair it wasn’t a straight forward question. This is also just my own attempt at a laymen’s explanation, so anyone who reads this and something seems off call it out.
The short answer to why:
Environmental influences/factors create selection pressures that create opportunities for a strategies or mutations to emerge based on the environmental conditions during a certain period of time. It’s not a static, linear or finished process. It is ongoing and always changing and what emerged as successful as one time or place will not of the conditions change.
I asked my 8 year old a simplified version and she said well what about the pretty colors, could that be a reason? It is a reason for flowers right, look at my little maple it is more colorful than any flower in our yard right now.
Dropping the leaves reduces possibility of predations but could it also be a dual function? Solid hypothesis for an 8 year old.
Random non scientific thought if you were deadset on trying to make it work in your environment.
Do you have the space and ambition to dig a decent size whole in the ground and try to create a microclimate using the earths insulatatory properties like cooler?
This is probably not going to work, especially without allowing for an escape root to go deeper into the ground than we would prefer for bonsai cultivation but only one way to know for sure!
I actually only mentioned this as stepping stone for someone else to come up with a better possible solution other than selling the tree
Water mobility. Broad leaf trees move a lot more water than a conifer. And Elms are on the faster water mobility of broad leaf trees too. I experience the same with my elms. Oddly though my beech go fully leafless, so it makes me think that elms are not as influenced by day light hours as other deciduous or semi deciduous trees, rather temperature for them more so
changes in photoperiod and/or temperatures are the two main factors that initiate dormancy. It is not necessarily one or the other, a combination or crossing a threshold point are possible and it is species dependent.
I’m still not 100 on my way forward, though I can guarantee it won’t involve big ground holes or refrigeration of my shed. My wife will put up with only so much.
I guess my plan will be to treat the tree with a level of detail and care that my other tree’s receive, and in 2 years if I notice a drop off in health I’ll see if one of the members of my club that lives in the cooler mountains will look after it until I sell it, or maybe they take it on consignment
