Is the climate zone info accurate enough for bonsai?

Hi everyone.

I was impressed with everyone adding their climate zone to their profiles when I joined the forum, so I looked up mine, cross referenced it and found I was zone 9 - the maps say 9b. While this broad classification gives a starting point I find it actually bears very little relevance to the exact trees that are kept successfully as bonsai, and many threads will state an individual will struggle or fail with a tree based on the climate zone info when others seem to do OK with it.

The local climate is extremely variable for one thing - on the coast (6 miles from me) a friends garden gets no frost to speak of and he has completely given up with white pines as they waste away in the wet mild conditions. 25 miles from me a valley slope produces the UKs only Tea, and this year they have picked in every month. Our small town has had night time temperatures of -3 to -4 this winter with days hovering at zero. (we only get 4 or 5 weeks like this each winter but it is enough for my white pines to be happy and healthy).

This shows localised climate variation, and within the bonsai area in the garden I get even more variety - one bench gets lots of winter sun, one only a little sun and remains frosted all day, one side reflects warmth from the back fence and the final side is totally exposed. Then there is the usual cold greenhouse and indoor garage with growlights for artificial conditions. Because we can offer such variation, and actually move the trees around I'm finding the climate zone information related to a tree or shrub of very little use when choosing which bonsai to grow.
These trees all do really well for me so makes you wonder; Scotts pine 3 -7, White pine 3-8, beech 4-7, cherries 3-7, etc and in surrounding gardens too, so either the species information is a little innacurate or not applicable to bonsai..

Any thoughts and similar observations?

Cheers Marcus

Marcus

Keep in mind the hardiness zone recomendations for plants are for specimines in the ground. In a bonsai pot life is of course very different.

Also micro climates abound as you point out even from bench to bench. Up here I'm technically 5b but I garden as though I'm in zone 5.

Experience has taught me not to trust the Hardiness maps.
-Jay

The USDA hardiness zone maps only record one variable, the average minimum winter temperature. The way this relates to bonsai, it tells you which species can spend the winter outdoors with the pot in the ground, which species spend the winter in the garage or other sheltered area, & which species spend the winter indoors. There are many other factors to consider. Your Zone 9 is quite different from Zone 9 in California.
Iris

Hi,
Thanks Iris and Jay,

I think with what you say as well it concludes the hardiness zone figures are basically of little use for bonsai. As you point out they show a relative winter ability to survive unprotected and planted in the ground, something that really does not apply to the bulk of our trees. The figures I'm really finding completely wrong though are the ones indicating a zone is too mild in winter to grow a species.

On paper Cornwall is too mild for beech, cotoneaster, all pines and many others - but these grow everywhere you look - the slope behind my house is mature beech and pine trees while virtually one house in three has cotoneasters growing in the garden somewhere.
I can see the fine line with Japanese white pines - the very mild gardens do struggle to keep one strong and healthy over time where I am doing OK by purposly exposing the trees to the coldest part of the garden I can find, with the junipers too - the cold is good & I find foliage growth is 'tighter'. The 'hot' trees seem far more accurate - Bougainvillia leaves drop off for me and it would be borderline to leave one outside all year - I think it would die.

As you say Iris Cali and Cornwall are very different ! but on paper have the same ave. winter temperature - I think the USA, due to its size has a far greater stability where we are only a few miles across really and can be effected by the Atlantic, the Gulf Stream, or even cold air dropping from Iceland - and all in the same week ! .

Would I be correct in saying the system was designed by and for the USA? as it seems perfect for continental sized land masses with a largely stable weather pattern.

cheers for the input,

Marcus

I'm not at all sure who is responsible for the worldwide climate zone maps. As far as I know, the USDA did the research an developed the map ONLY for the USA. The maps for Europe, and the southern hemisphere may be simple extrapolations, or some other entity may have done the research needed to produce definitive maps.

I think I'd tend to believe they are simple extrapolations, and as such, I wouldn't pin too many bonsai decisions on them.

In the USA, the American Horticultural Society has developed a heat zone index which is fairly useful. I think you can find it on the AHS website. And Sunset magazine has developed a detailed set of climate zones for the western United States which take more than minimum winter and maximum summer temperatures into account. Last I looked, these maps were not online, but if you buy a garden book -- like one of the more recent editions of its out-of-print classic "Bonsai" -- these detailed maps are reproduced in them. There is a similar map for the southeastern USA in garden books published by Southern Living Magazine.

What -- or if -- anything similar is available elsewhere I do not know.

I think having the zone numbers listed is useful, but only in a general sense. The U.S. zones are based on average minimum temperature - but a lot of other variables factor in plant survival. How much wind, how much snow cover, how many hours below a particular temperature, etc. A plant buried under a foot of snow might be able to survive -10 F, but that same plant fully exposed might perish. And average minimum temperature can be significantly higher than the potential minimum temperature. In my zone 6 location (Rochester, NY) the average lowest temperature each winter is about -8 to -10 F, but the all time record low is -22 F. Many areas have larger ranges between the average low and record low (we are somewhat tempered here by the proximity to Lake Ontario).

Then there are the longer term variations in climate...you could easily have 5 or 10 years where the weather patterns favor milder conditions - which allow plants at the edge of hardiness to thrive. Then a return to normal cold could set them back or kill them.

Variability...I don't know how we compare, but earlier this winter the temperature here went from 0 F to almost 50 F in about 24 hours.

Alls I know is I wished I lived in a climate like Cornwall or Oregon. I am freaking sick of struggling with cold weather related issues and landscapes so limited by hardiness. Minnesota is a nasty place for planst to live. It would be a joy to be able to have the lushness and beauty of these milder environs let alone be able to leave things under their benches for winter. But alas, not being wealthy and also having a local client based craft ties me to my land here.

Even so my bonsai are protected in the winter and never really get below 25 degrees F. I have given up on certain plants because of our tough springs here: one being trident maple.

My sympathies from Zone 5. Have you considered growing a few tropicals under fluorescent lights?
Alas, skiing is also expensive.

[quote="coh"]I think having the zone numbers listed is useful, but only in a general sense.
Hello,
I like to know the hardiness number to get an idea of the circumstances,
but knowing the zone number from a poster is only useful in a general way indeed.
I think each gardener knows the open spots in the garden where there is always the first frost.
Here i got for example 0 celsius in one part while having -2 or -3 celsius already in an other part.
Knowing your micro climate and the differences in your garden is important so you can use them.
Sunip