Ever Use Ice To Stimulate Cold Dormancy/Chill Hours

[Clicio]

We have a member who grows acer palmatums in the Azores which is a USDA zone 11, which means winters are only about this cold (i.e., somewhere around 7C).

I am in zone 11a, São Paulo, and I've been growing maples, pines, quinces, elms, prunus, junipers.
What has happened over winters?
Plants that stopped growing completely and totally lost their leaves:
Maples, Prunus Mume, Japanese Quince, Zelkova, Wysteria, one weird "deciduous" Bougainvillea.
Plants that stopped growing because they are evergreens OR didn't lose their leaves: JBPs, JRPs, Itoigawa Shimpaku, Chinese Elms, Satsuki Azaleas, Camellia Sasanqua.
Plants that didn't stop growing:
All tropicals including BRTs, Kumquat, Jaboticaba, Pitangas, Calliandra, Ficus Microcarpa, Chinese Fringe and Bougainvilleas. Last winter I had to shelter them for a couple of weeks when the temperatures dropped to less than 40f during the nights.
Now I ask: if the Maples lost their leaves and didn't show any signs of being alive for more than 60 days, and now are awake and growing, *weren't them dormant*?

 

[ShadyStump]

Now I ask: if the Maples lost their leaves and didn't show any signs of being alive for more than 60 days, and now are awake and growing, *weren't them dormant*?

Given the facts determined so far in the discussion, and your geography as well as planetary motions, they most certainly are dormant.
Remember that one factor in inducing dormancy is sunlight, intensity and duration. In your southern hemisphere winters the earth is at aphelion- the furthest the earth gets from the sun- whereas in the northern hemisphere winter takes place at perihelion- the earth's nearest point to the sun. In your winter the sun is significantly less intense, so it may take less cool nights for your trees to reach dormancy than in the northern hemisphere.

 

[leatherback]

In your southern hemisphere winters the earth is at aphelion- the furthest the earth gets from the sun- whereas in the northern hemisphere winter takes place at perihelion- the earth's nearest point to the sun.

interesting. Never really realized that. Had to do a bit of digging cause of it!

The UV index and its classification according to a scale of intensity of the sun

The UV index and its classification according to a scale of intensity of the sun. Prepare your trip. Where and when to leave? Climates and bathing temperatures in the tropics. Photos of the most beautiful beaches and lagoons in the world.

www.tropicsbeach.com

 

[Clicio]

Given the facts determined so far in the discussion, and your geography as well as planetary motions, they most certainly are dormant.
Remember that one factor in inducing dormancy is sunlight, intensity and duration. In your southern hemisphere winters the earth is at aphelion- the furthest the earth gets from the sun- whereas in the northern hemisphere winter takes place at perihelion- the earth's nearest point to the sun. In your winter the sun is significantly less intense, so it may take less cool nights for your trees to reach dormancy than in the northern hemisphere.

Thanks a lot for this very interesting piece of information, makes total sense.

 

[Leo in N E Illinois]

I thought the reason JM bonsai dont thrive in SoCal like conditions is the lack of temperature differential between day and night. Maybe I read that here?

I believe you read that correctly. But it applies to certain areas, for example around Los Angeles. Southern California is such a large area that some areas are just too hot and dry. Some areas are like Los Angels, not cool enough at night. And some areas are acceptable to grow Japanese maples. It is difficult to generalize. But probably a third of California is not climate friendly for Japanese maples. If you do not see them planted in the landscape around your town, they likely do not do well in your area for one of several possible reasons.

 

[cloudforest]

My experience here in Hawaii is that many Japanese maples need very little chill to grow. Without refrigeration, they go dormant in February and leaf out in May/June. Only takes as little as one month in fridge to cycle completely for early leaf out and I bet it takes even less fridge time.

 

[AJL]

Commercial fruit growers use this for fruit bud protection in orchards.You might like to take a look at this article:- in particular the section on overhead irrigation for icing which explains in more detail

https://njaes.rutgers.edu/peach/orchard/pdf/Frost-Protection-in-Orchards-Methods,-Updates-and-Costs.pdf