Coconut Palms In Zone 9b?

[PalmTreeDude]

I see coconuts in 10a + but can they grow in some parts of 9b? I have seen some in Sarasota (9b) and they seemed to look good, not sure if anything ever happens them from cold. What do you think?

Edited July 20, 2016 by PalmTreeDude

[tpr1967]

Hi, I live in Palmetto, Florida just off the south shore of Tampa bay and I just planted a 16' Coconut Palm in my yard. There are lots of Coconut Palms here on the beach and there are some were around 10-15 Coconut Palms that are fruiting right along the Manatee river in Palmetto. Were are you located?

[PalmatierMeg]

A true zone 9b has minimums of 25-30F. Without protection you can probably kiss a coconut good-bye if that minimum lasts more than a few minutes or temperatures don't rebound dramatically after sunup. Even then, that palm will show significant damage. Coconuts show foliar damage below 40F. If an unprotected coconut "looks good" after winter, it likely hasn't experienced a zone 9b winter. Down here in Cape Coral I am close enough to the Gulf that most winters since '09-10 (a zone 9b record-cold winter) that I'm a solid 10a or 10b. I also know that another record cold winter might wipe out all my coconuts. Coconuts pretty much disappear as you go east of US41. By Lehigh Acres there are none. Coconuts growing in St. Pete probably benefit from a zone 10 climate moderated by proximity of the Gulf. But, in general, the Tampa/St. Pete area is significantly colder than Cape Coral 100-120 miles south.

[topwater]

If coconuts could grow in a very warm 9b climate, you wouldn't be able to see my house from the street. 

Edited July 21, 2016 by topwater

[chinandega81]

I would say no. The ones you see in 9B are probably in microclimates which are actually 10A is my guess.

[tpr1967]

Global warming lol

[PalmatierMeg]

4 hours ago, tpr1967 said:

Global warming lol

Ack! Those words are verboten on this forum. They lure self-professed weather experts into screaming matches. Down, boy/girl, down!

[tpr1967]

34 minutes ago, PalmatierMeg said:

Ack! Those words are verboten on this forum. They lure self-professed weather experts into screaming matches. Down, boy/girl, down!

I don't really believe in it, I really love Meteorology, just saying that warmer part of 9B where I am seems to be getting warmer over all every year. So yes a Cold pattern like 2010 could kill off my Coconut Palm, over all I feel good about keeping it alive for a while. Besides the Palms just down the road from me survived 2010 very well.

[Xerarch]

Ok, so I keep seeing this title and keep thinking the same thing to myself, how do you know if you're in a strong 9b climate and not a 10a? Yes I know about all the published USDA zones maps, but they are a moving target and are just a general indicator anyway, there is no way to make a map that is accurate down to every city block with all the microclimates etc. 

You can install your own weather station and get your own average but you better be sure to have high quality equipment and excellent placement.  Even then, how many years do you have to average out? You could calculate that you are 10a with a handful of years of data and then all you need is one terrible winter to pull the whole average down solidly into 9b. 

I guess part of my point is that you might see coconut palms in an area marked as 9b in whatever USDA zone map you are looking at, but that doesn't mean that that coconut has actually experienced a 9b climate in that location, it could be in a favorable microclimate, or that area is a 9b because the 1989 freeze pulled the average down to 9b, but for the 5 or 10 years that the palm in question has been there, it has only seen rare and light frosts that have not killed it. 

I don't mean to make the question more complicated than it needs to be, but mankind tries to box up and categorize nature in ways that help us understand it, yet nature isn't interested in behaving in ways that are easily segregated into our nice little ideological boxes. So can a coconut survive in 9b? Well, I say no, but 9b on a map doesn't tell the whole story. 

Hope this made some sense. 

[Mohsen]

I am growing this little baby here in Sydney in 10a+..................of course only inside

But soone or later I will have to take it out and then ...It will be its last days when winter comes ...

I wish someone or some scientific centers  would have done some genetic alteration to Cco so they can stand 9b or even 9 a ...just imagine how world would be more beautiful then

[Xerarch]

1 hour ago, Mohsen said:

I am growing this little baby here in Sydney in 10a+..................of course only inside

But soone or later I will have to take it out and then ...It will be its last days when winter comes ...

I wish someone or some scientific centers  would have done some genetic alteration to Cco so they can stand 9b or even 9 a ...just imagine how world would be more beautiful then

Plus for guys like you it would be nice if they engineered some cool tolerance into them even if they still didn't like freezing temps, there could be cocos all over places like Sydney and coastal California. 

[PalmatierMeg]

Creating a more cold tolerant coconut or Cocos hybrid has been a wish of many coconut lovers since before I joined PT. Climate is a fluid and variable thing, so it is very difficult to reliably peg it within a half or even full zone although I can reliably predict I won't see zone 6 temps in my 10a location (so what?). Coconuts can be thought of as "canaries in the coal mine" for me where winter is concerned. The USDA zone system is far from perfect but is at least an attempt to quantify weather trends. I know my coconuts are at risk for an unusually bitter arctic freeze. I also know growing Cyrtostachys outdoors year round is a waste the palm's life and my money, so I don't even try

[Phil Stager]

We've had  several Jamaica Talls at the Kopsick Arboretum on the waterfront in St. Pete for twenty years or more.  Most of the ones in my neighborhood in the south end of St. Pete died after two cold and wet winters a few years back.  Lots of them showing up again.  Know your own microclimate if you want to grow them.

[PalmTreeDude]

19 hours ago, Xerarch said:

Ok, so I keep seeing this title and keep thinking the same thing to myself, how do you know if you're in a strong 9b climate and not a 10a? Yes I know about all the published USDA zones maps, but they are a moving target and are just a general indicator anyway, there is no way to make a map that is accurate down to every city block with all the microclimates etc. 

You can install your own weather station and get your own average but you better be sure to have high quality equipment and excellent placement.  Even then, how many years do you have to average out? You could calculate that you are 10a with a handful of years of data and then all you need is one terrible winter to pull the whole average down solidly into 9b. 

I guess part of my point is that you might see coconut palms in an area marked as 9b in whatever USDA zone map you are looking at, but that doesn't mean that that coconut has actually experienced a 9b climate in that location, it could be in a favorable microclimate, or that area is a 9b because the 1989 freeze pulled the average down to 9b, but for the 5 or 10 years that the palm in question has been there, it has only seen rare and light frosts that have not killed it. 

I don't mean to make the question more complicated than it needs to be, but mankind tries to box up and categorize nature in ways that help us understand it, yet nature isn't interested in behaving in ways that are easily segregated into our nice little ideological boxes. So can a coconut survive in 9b? Well, I say no, but 9b on a map doesn't tell the whole story. 

Hope this made some sense. 

I always look at the constantly updated Interactige USDA map. It is pretty accurate. 

Edited July 22, 2016 by PalmTreeDude

[PalmatierMeg]

I had a guy in Tennessee ask me, sincerely, if he could grow royal palms in his yard. May sound trite but is oh-so-true: if no one in your geographical area grows a certain plant there's a good reason why.

[Mohsen]

4 hours ago, PalmatierMeg said:

I had a guy in Tennessee ask me, sincerely, if he could grow royal palms in his yard. May sound trite but is oh-so-true: if no one in your geographical area grows a certain plant there's a good reason why.

Not necessarily true... In our neighbors you can see only 1 or 2 types of palms... But surely you could grow hundreds types at least here... There is some prejudice against palms here, I guess mostly due to untidy queen palms with their lots of problematic fruits...even nurseries near here have only up to type of palms if they have any at all...

[JEFF IN MODESTO]

5 hours ago, PalmatierMeg said:

 May sound trite but is oh-so-true: if no one in your geographical area grows a certain plant there's a good reason why.

Crazy how people don't see something growing in their location , they assume that's because you CANT grow it. ( or others would have already ....right!)

I have had bananas and rare palms growing and fruiting in my garden ....unprotected for over 20 years.

So when the news media comes out and does a story on TV.... someone will go looking to buy one of these  at a local master gardener nursery.

I had more than one people tell me that the local nursery told them its impossible to grow ( they even suggested that I have a greenhouse ! )

Or even worse, the nursery will order super frost sensitive plants, just to make a quick buck.... then complain when they die!

[Ben in Norcal]

1 hour ago, JEFF IN MODESTO said:

Crazy how people don't see something growing in their location , they assume that's because you CANT grow it. ( or others would have already ....right!)

I have had bananas and rare palms growing and fruiting in my garden ....unprotected for over 20 years.

So when the news media comes out and does a story on TV.... someone will go looking to buy one of these  at a local master gardener nursery.

I had more than one people tell me that the local nursery told them its impossible to grow ( they even suggested that I have a greenhouse ! )

Or even worse, the nursery will order super frost sensitive plants, just to make a quick buck.... then complain when they die!

I agree, Jeff...this is a totally invalid way of assessing possibilities in at least our location.  Very few people grow tropicals or semi-tropicals of any sort in Norcal...even totally bulletproof things.  Great example - you see almost no jacaranda here, and yet they are totally bullet proof.  Very tough to find any Brahea of any size, and totally bullet proof.  Almost no Archontophoenix in the Bay Area, yet bulletproof in some microclimates.  Experimentation is the only way to figure out what works IMO.

[PalmatierMeg]

People grow some types of cold hardy bananas in the Midwest. But no microclimate in TN supports a royal palm.

[velutina]

I lived in Salt Lake City (zone 6b/7a) for many years and my house was the only house that i ever noticed in the area that had bananas or bamboo. It was too cold for palms in the ground, but they made their appearance in pots during the summer. The bamboo has been going strong for 10 years+ 

I have seen coconut palms in Florida zone 9 that look really good! The ones I have seen have been fairly short. There are plenty of areas in Florida where coconut palms will grow for many years and look great. But there is always that cold front that reaches far south that devastates much of Florida for a few days...  It only takes a few days every few decades to erase decades of growth. 

 

Edited July 23, 2016 by velutina

[Dave-Vero]

Leu Gardens in Orlando has long propagated its own palms from seed and planted them out.  Some do well, and occasionally there's a destructive freeze.  But often as not, the palms live long enough to be worth having.  It also helps that the garden, next to a lake, has a highly protected microclimate next to the shore, under live oak canopy.  

My 10a climate is marginal for coconuts.  Two cold winters in a row, culminating in a 26º F (-3 C) freeze, killed many coconuts and badly damaged more.  The survivors are now in robust good health and the town had probably its best-ever crop of nuts.  

Locally, I think Kentiopsis oliviformis may work better than coconuts.  Archontophoenix is worth growing, but most will suffer leaf damage in bad winters.  Satakentia suffers leaf damage and might die in a worst-case freeze.   

[Xerarch]

2 hours ago, velutina said:

I lived in Salt Lake City (zone 6b/7a) for many years and my house was the only house that i ever noticed in the area that had bananas or bamboo. It was too cold for palms in the ground, but they made their appearance in pots during the summer. The bamboo has been going strong for 10 years+ 

I have seen coconut palms in Florida zone 9 that look really good! The ones I have seen have been fairly short. There are plenty of areas in Florida where coconut palms will grow for many years and look great. But there is always that cold front that reaches far south that devastates much of Florida for a few days...  It only takes a few days every few decades to erase decades of growth. 

 

I've seen Trachy's in the ground in SLC that have survived many years unprotected, one guy in Sugarhouse had one in his back yard that probably had a good 8 feet of trunk, it was well over his back yard fence.  He also had needle palm and Sabal minor unprotected. 

[velutina]

2 hours ago, Xerarch said:

I've seen Trachy's in the ground in SLC that have survived many years unprotected, one guy in Sugarhouse had one in his back yard that probably had a good 8 feet of trunk, it was well over his back yard fence.  He also had needle palm and Sabal minor unprotected. 

That's surprising! I'd love to see pics. I think it would be possible for a few years at least before you get a serious cold front. The only place in Utah i've seen palms survive in the ground is 3-4 hours south in St. George (zone 8a/b)

[Cape Garrett]

On 7/20/2016, 7:35:03, PalmatierMeg said:

A true zone 9b has minimums of 25-30F. Without protection you can probably kiss a coconut good-bye if that minimum lasts more than a few minutes or temperatures don't rebound dramatically after sunup. Even then, that palm will show significant damage. Coconuts show foliar damage below 40F. If an unprotected coconut "looks good" after winter, it likely hasn't experienced a zone 9b winter. Down here in Cape Coral I am close enough to the Gulf that most winters since '09-10 (a zone 9b record-cold winter) that I'm a solid 10a or 10b. I also know that another record cold winter might wipe out all my coconuts. Coconuts pretty much disappear as you go east of US41. By Lehigh Acres there are none. Coconuts growing in St. Pete probably benefit from a zone 10 climate moderated by proximity of the Gulf. But, in general, the Tampa/St. Pete area is significantly colder than Cape Coral 100-120 miles south.

I agree with Meg.  Coconuts are pretty much hardy from Pinta Gorda and southward on the west coast.  Those that did die in Southwest Florida during the freeze of '09-'10, were pretty much diseased or not well taken care of to begin with.  Those further north, if not immediately on the coast or in a reliable microclimate of a solid 10a, should be taken as a temporary resident.  Even rare to see these in the Orlando area with spots of a 10a climate...like I said... temporary resident.

[Xerarch]

On 7/24/2016, 12:35:18, velutina said:

That's surprising! I'd love to see pics. I think it would be possible for a few years at least before you get a serious cold front. The only place in Utah i've seen palms survive in the ground is 3-4 hours south in St. George (zone 8a/b)

Boy I wish I knew where the pictures were, I took some in the stone-age 90's before I had a digital camera so I have (had?) a hard copy photo of it but have no idea where it might be.

[Walt]

When I first  bought my property just outside the town limits of Lake Placid, in Highlands County, Florida, about 95% of the county was rated as zone 9a. But I found some mature (fruiting) coconut palms growing along lake front locations, and also some growing on high ground on the Lake Wales Ridge (where it runs about 8 degrees warmer on radiational cooling nights. Some years later when the new USDA hardiness map came out, Highlands County got a USDA zone 9b rating.

But what is a 9b rating? The 9b rating runs the gamut. 9B could be an area that sees 25 degrees and long duration spells below 30 degrees dozens of days each winter, along with low daytime highs. Or, it could be an area that is zone 10a or above all winter long except for a few minutes of just one day where it dipped to 29.9 degrees for a few minutes, with daytime temperatures relatively high.

If an area where the latter (as I stated above) holds, coconuts could grow without much of a problem except for the typical winter potassium deficiency they get.

I've been growing a coconut palm for about 12 years now, starting from about a 7 gallon size. I'm in a zone 9b location. My palm gets severe potassium deficiency every winter, and by winter's end the bottommost 10 fronds die very quickly come spring. My coconut palm is just now growing out of its winter potassium deficiency, and by December should be holding near a full crown of fronds again.

The past four winters my coconut palm hasn't required any form of protection, but in previous winters, especially January of 2010, and again in December of 2010, I had to wrap the trunk and meristem with heating cables, then wrap insulative coverings over them (to hold in the small quantity of heat from the heating cables). Had I not protected my coconut palm it would have surely perished from the ultimate low temperatures and prolonged days of cold.

My view about coconuts growing in zone 9b is that for all intents and purposes -- no, they won't grow there, at least for long. But in the extreme upper end of zone 9b coconuts will, and do, grow.

Even though my general area is zone 9b rated, around the lakes and on high ground is mostly zone 10b on a normal winter. Even on the coldest day in 2010 it never dropped below 32 degrees lakeside. Hence, if someone unfamiliar with microclimates and mesoclimates around here, they would see mature fruiting coconuts and determine they could grow in zone 9b -- even though they are really in zone 10a or higher due to the micro or meso climate they are growing in.

My fruiting coconut palm as of July 26, 2016. It's been a slow grower and has only just over 6 feet of clear trunk after being in the ground 12 years from a 7 gallon size.

[wrigjef]

Walt, your palm looks great. I was wondering how it was doing. You posted this pic on one of my threads in Sept 2012 so it has put on some nice growth.  I planted mine in the ground in February. Here is you Palm 4 years ago. 

[RedRabbit]

I'd put them at an avg annual low around 34f in Florida. That's 10a, but closer to 10b than 9b... They'll survive a few years in 9b but that doesn't count for much imo. 

[Zeeth]

1 hour ago, RedRabbit said:

I'd put them at an avg annual low around 34f in Florida. That's 10a, but closer to 10b than 9b... They'll survive a few years in 9b but that doesn't count for much imo. 

I think it depends on how long term you mean. They grow alright near the Sarasota Airport, which is right around 29˚ F for the average low. That factors in 1989 and 1962 though, which were quite cold and killed probably all of the coconuts. Anna Maria is right around 35˚ and has pre-'89 coconuts (and a few from before 1962 that survived all of the construction that's happened since then). You're probably right if you mean long-term, but they do okay for 20+ years on the very warmest edge of 9b. 

[Jim in Los Altos]

Why not just plant Beccariophoenix alfredii. Plenty of hardiness and looks amazingly like a true coconut without the winter worries.

[Walt]

4 hours ago, wrigjef said:

Walt, your palm looks great. I was wondering how it was doing. You posted this pic on one of my threads in Sept 2012 so it has put on some nice growth.  I planted mine in the ground in February. Here is you Palm 4 years ago. 

Yes, that was in January of 2010 (a very cold month) when I protected my coconut palm using heating cables and insulation wraps (flannel sheets). I had to protect it again in December of 2010 (an even colder month, where I set an all-time record low of 20.8 degrees in the open yard). My coconut palm's fronds got fried, but since I protected the meristem and trunk, there was enough starch reserves to start regrowing new spring fronds, then photosynthesis started producing new food for the palm. Fortunately, the past four winters I haven't dropped below 30 degrees (coldest of the four), so I haven't had to use my protection methods.

Several months ago a bunch of coconuts (11 of them on the bunch) fell off. I knew they were immature. I opened one up and sure enough it wasn't ready. Now I'm thinking about plucking one nut off (the matures looking of them) and see how it looks and tastes. I've harvested a few nuts for the past two years. They were very tasty.

I feel as long as I protect my palm's trunk and meristem I can grow it indefinitely. However, it will be harder to protect the trunk and meristem the taller it gets.

Right now my coconut palm is doing fine. I'd say by the end of fall it will look much better as it will be holding several more fronds and look fuller. I took the below photos today:

 

Above Photo: My coconut palm as it looks today, August 15, 2016

Above Photo: Coconuts with my ZTE cell phone for scale

 

 

 

[Zeeth]

29 minutes ago, Jim in Los Altos said:

Why not just plant Beccariophoenix alfredii. Plenty of hardiness and looks amazingly like a true coconut without the winter worries.

Why not both? Really though, I think we'll start seeing a lot more use of B. alfredii in landscapes in Central Florida in the next few decades (and presumably other 9b parts of the country as well). It's too bad they don't grow as quickly as coconuts though. 

[GottmitAlex]

1 hour ago, Walt said:

Yes, that was in January of 2010 (a very cold month) when I protected my coconut palm using heating cables and insulation wraps (flannel sheets). I had to protect it again in December of 2010 (an even colder month, where I set an all-time record low of 20.8 degrees in the open yard). My coconut palm's fronds got fried, but since I protected the meristem and trunk, there was enough starch reserves to start regrowing new spring fronds, then photosynthesis started producing new food for the palm. Fortunately, the past four winters I haven't dropped below 30 degrees (coldest of the four), so I haven't had to use my protection methods.

Several months ago a bunch of coconuts (11 of them on the bunch) fell off. I knew they were immature. I opened one up and sure enough it wasn't ready. Now I'm thinking about plucking one nut off (the matures looking of them) and see how it looks and tastes. I've harvested a few nuts for the past two years. They were very tasty.

I feel as long as I protect my palm's trunk and meristem I can grow it indefinitely. However, it will be harder to protect the trunk and meristem the taller it gets.

Right now my coconut palm is doing fine. I'd say by the end of fall it will look much better as it will be holding several more fronds and look fuller. I took the below photos today:

 

Above Photo: My coconut palm as it looks today, August 15, 2016

Above Photo: Coconuts with my ZTE cell phone for scale

 

 

 

Very nice!! Congratulations. Once it gets taller you might consider couple IR heat lamps trained on the meristem.

Since you mentioned the past four winters have not seen temps below 30, I must say, that is one uber-hardy coconut palm.

Gives me a bit of hope for my palms come winter.

Here again, felicitations on your coconut palm. Against all odds.

[RedRabbit]

7 hours ago, Zeeth said:

I think it depends on how long term you mean. They grow alright near the Sarasota Airport, which is right around 29˚ F for the average low. That factors in 1989 and 1962 though, which were quite cold and killed probably all of the coconuts. Anna Maria is right around 35˚ and has pre-'89 coconuts (and a few from before 1962 that survived all of the construction that's happened since then). You're probably right if you mean long-term, but they do okay for 20+ years on the very warmest edge of 9b. 

I have the Sarasota Airport at 32.56F since 2000... The areas of 9b where they survive 20+ years aren't really 9b (St. Armands for example.) I largely disregard what USDA says and just calculate it on my own when I'm curious. By my calculations, warm 9b areas include the Daytona Airport, USF, Mayport (JAX), the Lakeland Airport, and none those locals can support coconuts for more than a few years. If somewhere in Florida is legitimately is 9b there's just not much hope for coconuts.

 

5 hours ago, Jim in Los Altos said:

Why not just plant Beccariophoenix alfredii. Plenty of hardiness and looks amazingly like a true coconut without the winter worries.

Well, they're kind of slow... 

[Walt]

11 hours ago, GottmitAlex said:

Very nice!! Congratulations. Once it gets taller you might consider couple IR heat lamps trained on the meristem.

Since you mentioned the past four winters have not seen temps below 30, I must say, that is one uber-hardy coconut palm.

Gives me a bit of hope for my palms come winter.

Here again, felicitations on your coconut palm. Against all odds.

I've been in the winter protection mode for 18 years now. I've used heat lamps, kerosene forced air heaters, propane forced air heaters, propane infrared heaters, space heaters, electric griddles/frying pans, and heating cables with insulation wraps and/or tents -- depending on the size of the palm/plant I was trying to protect.

I can tell you that trying to protect a large spreading palm during a night in the 20s F, sub 0C (radiational cooling, let alone advective cooling), one may as well forget heat lamps or heaters -- as it would take way too many of them. The heaters just can't provide the massive amount of BTUs to fully protect the entire palm 360 degrees around the palm.

When my coconut palm was small I used to use propane and kerosene forced air heaters to protect it. I assisted the heaters by erecting a tarp (using tall poles to mount the tarps on) to encompass 180 degrees around the palm. Then I placed two heaters to blow on the opposite side of the palm the tarps were on. The tarps help keep the warm air from the heaters around the palm (if you can envision that). This worked okay on radiational cooling nights.

But after my palm got too big to bundle the fronds I finally had to accept the fact that the fronds were going to get frost/cold damaged. At that point I just resorted to my catastrophic protection mode: spirally wrapping a heating cable around the trunk from the soil level, up and past the meristem, then wrapping the same with insulation blankets.

The blankets held the heat from the heating cables (which is minimal), and is the key to keeping the palm trunk and meristem from freezing. The fronds may get fried but the rest of the palm is unhurt from the cold. This is very important for the meristem. I found by keeping the meristem from being cold damaged the new spring fronds aren't stunted. I've found this to be a fact with respect to my coconut palm and my African oil palm.

There was a time when I went all out and protected so many palms and shrubs, but those days are over for me now. The only palms I will protect now is my coconut, by large adonidia growing at the S.E. corner of my house, and my African oil palm. Nature will just have to take her course on everything else. I'm hoping for another mild winter for 2016-17.

[Zeeth]

7 hours ago, RedRabbit said:

I have the Sarasota Airport at 32.56F since 2000... The areas of 9b where they survive 20+ years aren't really 9b (St. Armands for example.) I largely disregard what USDA says and just calculate it on my own when I'm curious. By my calculations, warm 9b areas include the Daytona Airport, USF, Mayport (JAX), the Lakeland Airport, and none those locals can support coconuts for more than a few years. If somewhere in Florida is legitimately is 9b there's just not much hope for coconuts.

Are you going back to 2000 for all of your data? I think that's the difference between our methods if you are. I go back to the 50's or so when I calculate it (I've also got a master chart going). 

[RedRabbit]

30 minutes ago, Zeeth said:

Are you going back to 2000 for all of your data? I think that's the difference between our methods if you are. I go back to the 50's or so when I calculate it (I've also got a master chart going). 

Yeah, only to 2000 which was somewhat arbitrary... If you average from the 50s I'd think the numbers you get for most locals would be 2-4f colder. I wouldn't go back that far due to all the urbanization that's taken place.  

[Zeeth]

17 minutes ago, RedRabbit said:

Yeah, only to 2000 which was somewhat arbitrary... If you average from the 50s I'd think the numbers you get for most locals would be 2-4f colder. I wouldn't go back that far due to all the urbanization that's taken place.  

That's true, but without going back that far I wouldn't be able to capture the record cold winters like 1962 and 1989 in the data. The USDA numbers from their interactive zone map tend to line-up with my numbers pretty well, but you're right that the increased urbanization causes an issue. 

[Mandrew968]

On 7/20/2016, 7:35:03, PalmatierMeg said:

A true zone 9b has minimums of 25-30F. Without protection you can probably kiss a coconut good-bye if that minimum lasts more than a few minutes or temperatures don't rebound dramatically after sunup. Even then, that palm will show significant damage. Coconuts show foliar damage below 40F. If an unprotected coconut "looks good" after winter, it likely hasn't experienced a zone 9b winter. Down here in Cape Coral I am close enough to the Gulf that most winters since '09-10 (a zone 9b record-cold winter) that I'm a solid 10a or 10b. I also know that another record cold winter might wipe out all my coconuts. Coconuts pretty much disappear as you go east of US41. By Lehigh Acres there are none. Coconuts growing in St. Pete probably benefit from a zone 10 climate moderated by proximity of the Gulf. But, in general, the Tampa/St. Pete area is significantly colder than Cape Coral 100-120 miles south.

St. Pete low is about 28 degrees. My family has a house there, so naturally I plant stuff!

[Zeeth]

26 minutes ago, Mandrew968 said:

St. Pete low is about 28 degrees. My family has a house there, so naturally I plant stuff!

It depends on which area of St. Pete you mean. The warmest part of St. Pete near Kopsick is right around 35˚ for the average low.