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Mark_NoVA

10B zones in SoCal gardens

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Mark_NoVA

I've read a lot of comments on the board about the cold-hardiness requirements for palms in Southern California--sounds like the only frost-free areas are rare microclimates, and that typical winters, even in most of the San Diego area, see low temperatures below 30F. Does that sound accurate?

Recently, though, I noticed that a fair amount of SoCal-ians list their gardens as a 10B climate. :blink: Given the above, that doesn't make sense--10B corresponds to 35-40F. The minimum temperature requirements of most palms, except those in Lipstick Palm range should be fine for 10B.

If the above generalization is accurate, though, these SoCal gardens should be considered 10A or even 9B/10A.

So out of curiosity, what is happening here--are there some actual 10b microclimates, is there some wishful thinking going on, or is there a different understanding of the USDA zone system than I'm presenting here? (Or weak math skills or Dr.Darian-envy? :lol: )

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epicure3

That's because your impressions are about as wrong as they could be. Most of San Diego below, say, 3000ft and within several miles of the coast, rarely ever see temps below 30F (35F would be rare). I rarely ever see temps below 38. There are microclimates along the coast where cold air drains that are probably 10A.

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MattyB

I believe that I have a 10b zone at the top of my hill and a 9b zone at the bottom of my canyon which is about 150 feet lower in elevation. The bottom of my canyon is still 200 feet above the bottom of Spring Valley where it flattens out and there's lots of houses, but I think I get colder due to the sharp walls of the canyon concentrating the flowing cold air into a very narrow area. But it doesn't take that much elevation change to make cold pockets on dry still nights. Something as simple as a slightly inclining backyard and a closed side gate can trap air in a side yard making it a zone colder. If you've never been here on a still, dry, santa ana night then it might be hard to get a sense of our microclimates. I've had 31F on several occasions w/ no frost due to low humidity. And even when there is frost it's often only on the grass and 5 feet above the ground it can be 5-8 degrees warmer. I suspect you don't get many single digit humidity readings in North Virginia. These dry nights are our cold fronts and the freeze/cold comes via radiational freezing, not from a moist windy cold front. Sorry, I don't mean to be accusatory saying, "you don't understand man!!!!" because really I don't understand it fully myself. Maybe someone like Happ can explain it better.

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freakypalmguy

I'm a zone 9er at the top of my property and an 8er at the bottom. Similar to Matty's just minus a zone. I guess you could say I have "zone envy". But there are definitely 10's in Caleefourneea.

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Mark_NoVA

Thanks for the info, and it's true that I actually don't understand! (And have worse zone envy.) I was surprised when I first started on the forum reading about San Diegans wanting 'cold hardy' palms and wanting to move to Hawaii so they could grow more palms (a classic 'the grass is always greener...', given how nice San Diego is already). And read lots of posts on freeze/frost damage and the importance of canopy there, etc. I'd just read this old thread too: Are locations in California "frost-free"?, Where? So I was wondering, how can there be 10b gardens? (Maybe zone-envy wasn't limited to us cold-region guys.)

Here, it certainly doesn't get dry in the winter like it can there (you guys would laugh at what a 'drought' is), but we do get radiational freezes sometimes, which cause less-predictable, more uneven low temps across the region.

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mnorell

The south-facing, air-drained slopes of the Santa Monica Mountains running through Brentwood/Westwood/Beverly Hills/Hollywood represents a large swath of mostly 11A land. Canyon-bottoms and canyon-mouths being of course colder. The UHI of L.A. has certainly helped to make that a reality. I think it's safe to say that Avalon (Catalina Island) and perhaps Coronado, Point Loma and La Jolla can claim the same. In any event, it's small areas rather than large geographic areas. There are more 10B and 10A zones adjacent to all these areas. But of course topography makes a huge difference. I was told by an Encinitas orchid grower that in the '07 freeze, there were cold-air-basin areas within sight of the ocean in Del Mar that saw teens while nearby slopes in Cardiff, etc. were running just above freezing. Even the Sunset zones are coarsely defined and could certainly stand some tweaking!

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BS Man about Palms

Also Mark, There has been the discussion as to whether that zone rating is really accurate for our growing conditions. I believe it was Florida based and even though they may have lower "drops" than we do, we "stay cooler" longer during the winter.

If I could describe it like a house Thermostat where in So Cal during our summers, we'll say the average temps range from 55 at night to 90+ during the day, during winter its more like 40to 68/72 range.

Where in much of Florida it still may be 50 at night and 80 during the day thru much of the winter (which keeps growth good) occasionally someone "shuts the t-stat off for a day or so" and the night AND day temps will be VERY cold. (In So Cal on our coldest nights we will still generally be in the 60's the next day, but Florida may only be in the 50's)

Very broad generalizations above to be sure.

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happ

This topic receives periodic attention with plenty of archival discussions. The irony that San Francisco's coldest minimum is warmer than Orlando points out the weakness of utilizing this formula. USDA zone 11 encircles the LA basin but even downtown & the airport have not experienced freezing temps in many decades. But the 40F\ 4.4C lowest minimum also includes many nights in the 40's in California. Viewing the frost damage recently posted in Florida I understand that it doesn't just take freezing temps to harm palms [i will post photos soon].

The variety of palms available to SoCal gardeners is quite extensive but growth rates are likely half of what is common in Florida & Texas at much lower latitudes.

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bubba

Happ, Your statement characterizing the fact that a location whose temperature remained 40F all year would qualify as Zone 11. This example demonstrates the fallacy best.What kind of tropical palms would grow in that environment?

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Tyrone
These dry nights are our cold fronts and the freeze/cold comes via radiational freezing, not from a moist windy cold front.

So Matty, are you saying that your cold fronts are generally dry? If so, that's where my climate is nothing like So Cal which it is sometimes compared too. A cold front that makes it as far north as Perth will normally bring cloud and rain of some sort. It could explain why we gets 3 times So Cal's winter rainfall. We never get advective freezes and some areas may get a radiational freeze on a clear still night. Some areas near the coast are true zone 11 never seeing below 4.5C ever. The same is true of Rottnest island. Generally speaking, even the lightest canopy will generate 10b conditions at the very least.

I find it interesting comparing climates.

Best regards

Tyrone

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Tyrone
Happ, Your statement characterizing the fact that a location whose temperature remained 40F all year would qualify as Zone 11. This example demonstrates the fallacy best.What kind of tropical palms would grow in that environment?

Ceroxylon, Leppidorachis, Chambeyronia lepidota.

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Paul The Palm Doctor!

Besides being over 40 F. (but way more over 55 F. nights!) for three months (in winter, which is our dry time), a Fla. Keys Zone 11 has minimum temperatures from May through Novermber of from 65-85 F., which tropical plants love. In summer the highs are still only 85-90 F (with 74 degree dew points. Ughhh!)

On the mainland from Palm Beach-Ft. Lauderdale-Miami, due to perhaps one or two or probably no nights below 40 F. in winter, we cannot be truly called "Zone 11" (and are instead Zone 10 B or 10 A, but save for just a night or two, it surely is a de facto USDA Zone 11 here! (I can feel it for sure on my wilted eyebrow, replete with salty sweat!) Tropical plants of all sorts grow like weeds here in SE Florida (and except for forays into the damaging/killing frost) in most of the rest of Florida, too.

Our southerly latitude and proximity to the Gulf Stream, warm Atlantic Ocean, warmer Gulf of Mexico, and our stable tropical jet stream of air would verify that.

The 20's & 30's F. begin to emerge from Port St. Lucie north and from North Fort Myers, north, and in the center of the state from the Everglades & north. Even these events are rare, but they occur just enough to "kick" these parts of Florida into the 10 A & 9 A-B zones (and even 8 B near Tallahassee!)

In summary, a Zone is "guidance" number (as is the Western US-orientated Sunset magazine zone map) except in a way more general, and the USDA Zones really DO work better east of the Rocky Mtns. where micro-climates don't come into play as much.

It's all about heat; tropical plants LOVE heat! (And a wee bit of nasty old cold!) :)

Paul

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epicure3
Happ, Your statement characterizing the fact that a location whose temperature remained 40F all year would qualify as Zone 11. This example demonstrates the fallacy best.What kind of tropical palms would grow in that environment?

Yes, the USDA zone maps are way outdated to use on a national basis. It must have been devised before anybody lived in California. The truth and the problem is that the California climate, specifically Southern California, is so unique to the pattern of climates in the rest of the US that I don't think that you could actually come up with a true to form cold hardiness map. I think the closest we have is the heat zone map. While it, too, has its faults, its a heck of a lot closer to reality than the hardiness map.

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MattyB
These dry nights are our cold fronts and the freeze/cold comes via radiational freezing, not from a moist windy cold front.

So Matty, are you saying that your cold fronts are generally dry? If so, that's where my climate is nothing like So Cal which it is sometimes compared too. A cold front that makes it as far north as Perth will normally bring cloud and rain of some sort. It could explain why we gets 3 times So Cal's winter rainfall. We never get advective freezes and some areas may get a radiational freeze on a clear still night. Some areas near the coast are true zone 11 never seeing below 4.5C ever. The same is true of Rottnest island. Generally speaking, even the lightest canopy will generate 10b conditions at the very least.

I find it interesting comparing climates.

Best regards

Tyrone

No Tyrone, we get the cloudy, rainy cold fronts that drop down from the northern Pacific. But because these approach from over water the coastal side of our local mountains don't see temps that are as cold as when we get a dry cold front that hits us from the back door continental US, dropping down Arctic air from Canada. These are the dry ones and usually the coldest.

GG-109.jpg

Check this out. This was taken up in the Topanga area which is the coastal mountains above Malibu. With coastal topography like this it's no wonder there are frost free areas around here. That's the Santa Monica pier down there.

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happ
Besides being over 40 F. (but way more over 55 F. nights!) for three months (in winter, which is our dry time), a Fla. Keys Zone 11 has minimum temperatures from May through Novermber of from 65-85 F., which tropical plants love. In summer the highs are still only 85-90 F (with 74 degree dew points. Ughhh!)

On the mainland from Palm Beach-Ft. Lauderdale-Miami, due to perhaps one or two or probably no nights below 40 F. in winter, we cannot be truly called "Zone 11" (and are instead Zone 10 B or 10 A, but save for just a night or two, it surely is a de facto USDA Zone 11 here! (I can feel it for sure on my wilted eyebrow, replete with salty sweat!) Tropical plants of all sorts grow like weeds here in SE Florida (and except for forays into the damaging/killing frost) in most of the rest of Florida, too.

Our southerly latitude and proximity to the Gulf Stream, warm Atlantic Ocean, warmer Gulf of Mexico, and our stable tropical jet stream of air would verify that.

The 20's & 30's F. begin to emerge from Port St. Lucie north and from North Fort Myers, north, and in the center of the state from the Everglades & north. Even these events are rare, but they occur just enough to "kick" these parts of Florida into the 10 A & 9 A-B zones (and even 8 B near Tallahassee!)

In summary, a Zone is "guidance" number (as is the Western US-orientated Sunset magazine zone map) except in a way more general, and the USDA Zones really DO work better east of the Rocky Mtns. where micro-climates don't come into play as much.

It's all about heat; tropical plants LOVE heat! (And a wee bit of nasty old cold!) :)

Paul

You have summarized the issue perfectly, Pablito. There is no way I can create the tropical paradise you have in Pembroke Pines & would love another visit some day.

Matty, beautiful shot :mrlooney:

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MattyB

Thanks Happ. If you like shots of our amazing topography check out this thread. I took some more pics up in Topanga this week.

linkydinky

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Hollywood Palms

I live in one of the "...The south-facing, air-drained slopes of the Santa Monica Mountains running through Brentwood/Westwood/Beverly Hills/Hollywood represents a large swath of mostly 11A" areas in the Hollywood Hills.

While it's true, for example, we never got frost in 07 and I have only had a couple of hours of below 40 degree weather this year, there are a few other considerations:

1. Light - in the canyons, we get less light, due to the very steep canyon walls. In the last part of December, I get my "sunset" at 2:30 p.m.! This certainly limits blooming, warmth and temps.

2. Water - we get more precipitation than the L.A. basin as the clouds literally stop at the top of the canyons before sailing over. Same thing with our summer fog. Some of the canyons have springs or seasonal creeks in them, as well. That being said..

3. Position in the canyon - At the tops and at the mouths of the canyons, temps fluctuate a great deal more and the exposure to the damaging Santa Ana winds is much greater. Those of us closer to the bottom of the canyons-not the mouth-have a more controlled climate.

4. Soil composition - the canyon sides are decomposed granite for the most part. The mouths are DG and clay. Having a soil that retains so much heat helps out a lot.

I think our 10b/11 zone should be called a "California 10b/11a" zone. Florida zone 10b/11 is a whole different animal.

My 2 cents.

David

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MattyB

Interesting observations David. My area has DG with a good bit of clay content on the tops and canyons and at the mouths/bottoms it can be very heavy clay too. I guess this is a function of millions of years of erosion bringing super small particles down the hill.

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Tyrone

"No Tyrone, we get the cloudy, rainy cold fronts that drop down from the northern Pacific. But because these approach from over water the coastal side of our local mountains don't see temps that are as cold as when we get a dry cold front that hits us from the back door continental US, dropping down Arctic air from Canada. These are the dry ones and usually the coldest."

That is where the west coast of Oz and the west coast of the US are different. In Oz we will only ever get cold fronts that come across water. When it rains here it's not that cold. We never get dry cold fronts coming over land like the US, because it's geographically impossible with no land below 35S on the west coast of Oz. All our cold fronts come from the same direction, without a real polar blast, although we may complain like we do get polar blasts in winter. We don't really.

Best regards

Tyrone

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