Horticulture/USDA Hardiness Zones- I just don't understand them


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Nipomo, CA
Total Newbie when it comes to these zones.

I live on the Central Coast of CA in Nipomo CA in between San Luis Obispo and Santa Barbara, CA. It looks like i'm somewhere in between a 7-9. I don't know what this means in terms of what plants I can and cannot grow. Can someone explain that too me? I'm thinking both Bonsai and for landscape trees.

Often when purchasing plants on line it will say the plant name then the zone. What does this mean

For example:
Prunus mume Zone 5

I dont' think Mume is Zone 5, but let's just say it is. Would this not grow well in my zone of 7-9?


Bill S

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Western Massachusetts
Yenling some basics as I know them, and it's not like I have gone looking for info.
Typically the main thrust is cold hardiness, How Low can that trees temp. go before its a gonner. How to interpret the border areas as you suggest you are in, could be the best approach is conservative use the higher # in you case(higher # = higher lowest tempreture the plant can take) lower # = lower temps can be withstood. To be safe use a wamer lowest tempreture that will do damage to the plant

Now there are factors that can throw the zone info out the window too, such as potted plants, the info is for plants in the ground, wind can do damage that temps might not, global warming is pushing the zone lines north.

Heat zone is a different story, and may not be the same as USDA zone, some where there is a heat and cold index not sure how they correlate.

Your best results will probably be to talk to knowledgeable people in you local that know the right answers, and fine tun for your direct application.

As alway somethings you get just will not line up to convention - my example for this would be Serrissa ( groan - I know the dreaded Serrissa) most people will tell you they are tropical to subtropical, I know of sevaral people tha have much better results treating it like a temperate tree and give it cold - which by almost every popular vote would yeild a dead tree, but it works and well, so just what zone do you lable it, I'd put it at maybe zone 6, it's probably labled as 8, 7 at best.

Hope these rambling help, if I said something you don't follow please say Huh?


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Northern Idaho
USDA zones are based on the average coldest winter temps.
The lower the zone # - the colder

When looking at a particulat plant, and it indicates a zone # - that zone is the coldest zone that the tree can be expected to grow in. In general, if you live in zone 7 (for example) then most plants listed for colder zones and up to Z7 will do well there. There are exceptions of course, especially for trees that require dormancy.
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