Cold hardiness - sustained or 'dip?'

Discussion in 'Outdoor Tropicals' started by DGuertin, Jun 3, 2008.

  1. DGuertin

    DGuertin Active Member 10 Years

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    Well, in focusing more and more on things I'm sure will survive here, I'm straying a little bit with this question... Still recovering from Zonal Denial Disorder. ;-)

    Reading up on hardiness of some palms, Caryota Urens, for example, I'm reading hardy to 22d F. Lovely, but is that a sustained temp of 22 degrees, or is that more the kill point? Main reasona I ask is that I have several quite nice palms ni my neighbourhood that IU'm led to believe should never have survived here to begin with.

    A lovely Chinese fellow up the street has six or eight Bottle Palms, Hyophorbe lagenicaulis, which are rated to Zone 10, with a minimum temperature of 28 degrees F. We hit 22 degrees a couple of nights this past winter, and not a one of these trees was phased in the slightest. No leaf burn, no death, nothing...

    So, I'm confused... Any insights on this one?
     
  2. joclyn

    joclyn Rising Contributor

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    microclimate possibly or if you're in zone 9b, then a lot of times, things that are rated a 10 would just manage to survive in the area that borders on the cut-off.

    zonal denial order...i like it. ;) have a touch of it myself...so i'm in the process of converting a room in the house into a semi-desert situation...
     
  3. DGuertin

    DGuertin Active Member 10 Years

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    Well, I suppose it's the climate ratings I'm having a prob with. I have this funny thing with buying bamboo, palms, ferns, primitive gymnosperms; I buy them with the intent of growing them, and having them survive... With some of these palms I'm seeing sustained ratings at zone 10 and a minimum temperature listed in the low 30's to upper 20's. Now, I'm seeing in the real world, in my own neighbourhood, these same trees that have gotten through nights in the low 20's and they weren't phased in the slightest. I suppose what I really want to find is the 'Kill Point' of some of these things without having to find out for myself. :-(
     
  4. Ron B

    Ron B Paragon of Plants 10 Years

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    If a reference doesn't define what their rating refers to specifically then you don't know. With temperatures it could be when the plant is expected to be killed or it could be when the plant is expected to be damaged. With zones it could be where the plant is expected to grow indefinitely without damage or it could be where the plant is on the edge of its hardiness, with damage or maybe even death occurring in the worst winters. The latter is likely with commercial sources in particular who may overstate the parameters a bit in an attempt to sell an item. Or the compiler of the listing or catalog may not understand the zoning system. This is common due it seems primarily to temperature ranges being given for USDA zones, many thinking these depict the range of absolute minimum temperatures to be encountered in the zone rather than the average annual minimum temperatures. If an area is zoned to USDA 9 (average annual minimum temperatures 20F-30F) then it is mistakenly thought that means it rarely if ever gets below 20F there - plants hardy to 20F-30F are then designated Zone 9 plants. In reality it will sometimes get below the average minimum temperature range given for each zone and plants that are to be grown there long term need to be hardy below that range. Some sources even recommend that you select plants rated one zone colder than the zone you are in.

    I believe the last time it got below 10F over a wide area in my part of USDA 8 was in 1990. Such episodes are not frequent enough to pull us out of the average range given for Zone 8 of 10F-20F; many winters it may not even get down to 20F. But when we do get into single digits there is rather abundant damage due to all the plants used here because they were rated Zone 8 based on them being hardy to 10F-20F.
     

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