Need better way than hardiness zone to compare palm viability in different areas

[DreaminAboutPalms 435]

There was to be a better way than hardiness zones to determine which palms are suitable in an area. I think what would make more sense is categorizing places by number of hours annually in each temperature range and also having a multiplier for average humidity, etc.

For example:

1.5 * (Hours between 15 and 20 degrees)

1.25 * (Hours between 20 and 25) 

and so forth. Cities/regions get a score.

The reason why is that you could have a 9B climate that averages a high of 39 and low of 28 in winter but is protected by mountains and never drops below that hardly. At the same time take a place like Texas where average lows in January are around 40 but you occasionally get years like 2021 where we got colder than central Ohio. Additionally in Texas, we get plenty of winter days where nighttime low doesn't drop below 55 and we get 70 degree days every week. 

New system needs to take into account:

-number of hours below freezing in 5 degree ranges

-number of days where temperature does not exceed freezing, continuous freezes

-solar radiation levels

-precipitation and humidity 

-wind direction. 

 

hardiness zones are a loose criteria for choosing palms. There are bigger filiferas in 7A New Mexico zones than in 8A areas along east coast. This would be a better way to compare individual climates 

 

 

Edited July 9, 2021 by DreaminAboutPalms

[kinzyjr 5,610]

Creating a gardening zone guide is a very tough thing to do for a number of reasons.  Much of the criteria you mentioned above is included in the opening post for the Cold Hardiness Master Data spreadsheet since that sheet attempts to capture the main freeze details of each post in regard to factors like wind, duration of cold, etc.  As the name of the post implies, it deals with observations during freeze events. 

There are other environmental factors that can eliminate a palm from a landscape palette in a region.  A factor that is often overlooked is heat.  Some are heat sensitive.  As a few examples, Juania australis and members of the Ceroxylon genus can just as easily be killed by high temperatures as temperatures that are too low.  While Trachycarpus and Jubaea are perfectly cold hardy enough to grow almost anywhere in Florida, there are only a few nice Trachycarpus around and few, if any, Jubaea.  For these two genera, it is often suggested that the duration of our hot and wet season combined with nematodes in our soil typically send them to the mulch pile.

Another issue is that high or low humidity could be a blessing or a curse, depending on palm species.  If you're growing mostly palms from desert, semi-arid, and Mediterranean climate regimes, low humidity and rainfall combined with available ground water will likely be much appreciated.  The palms in question will survive much lower temperatures than if they are struggling with fungal infections and root rot in a wet tropical or subtropical climate.  On the flip side, if you're growing Veitchia arecina here in high-9b/low-10a Florida where it is hot and muggy 9-12 months out of the year, you can sneak a few through mid-to-high 20s and they'll regrow their crown.  If you try the same thing in a foggy and cool 10a like coastal San Francisco, they'll likely just sulk and give up the ghost.

Addressing the problem in an accurate manner is extremely difficult unless you handle it on a species by species manner.  Whatever system is created would have to be able to add points if the species benefits from that particular climate regime, or subtract (or even multiply by 0) if it dislikes the climate and/or can't survive.  I just checked the Palms table I put together using Trebrown's table as a starting point, and that table now has over 2800 species listed (including hybrids).  Anyone motivated enough to attempt creation of a new zoning system for all of them gets a tip of the cap and well wishes from me.

[Sabal_Louisiana 138]

7 hours ago, DreaminAboutPalms said:

There was to be a better way than hardiness zones to determine which palms are suitable in an area. I think what would make more sense is categorizing places by number of hours annually in each temperature range and also having a multiplier for average humidity, etc.

For example:

1.5 * (Hours between 15 and 20 degrees)

1.25 * (Hours between 20 and 25) 

and so forth. Cities/regions get a score.

The reason why is that you could have a 9B climate that averages a high of 39 and low of 28 in winter but is protected by mountains and never drops below that hardly. At the same time take a place like Texas where average lows in January are around 40 but you occasionally get years like 2021 where we got colder than central Ohio. Additionally in Texas, we get plenty of winter days where nighttime low doesn't drop below 55 and we get 70 degree days every week. 

New system needs to take into account:

-number of hours below freezing in 5 degree ranges

-number of days where temperature does not exceed freezing, continuous freezes

-solar radiation levels

-precipitation and humidity 

-wind direction. 

 

hardiness zones are a loose criteria for choosing palms. There are bigger filiferas in 7A New Mexico zones than in 8A areas along east coast. This would be a better way to compare individual climates 

 

 

At least when it comes to palms, there is too much emphasis on the absolute low temperature endured during a trying cold event, which is what cold hardiness is based on.

Which of these would you rather experience:

5 days where the temperature got no lower than 21 but no higher than 40 during that period, with snow and ice for 2 days and at least one of those days failing to rise above freezing at all and each of those days below 26F each morning

3 days with clear skies, where the temperature briefly dropped to 18 on one morning but rebounded to 45-50 during the afternoon, falling again for one more night down to the low 20s and then back into the 50s, with gradual warming thereafter

In the first instance, this location would still qualify as acceptable for zone 9 but in the second case, no better than zone 8.