Here in the UK we have to put up with 3-4 months
of dull, cloudy days where the temperature rarely rises above 10°C
and night temperatures usually fall to a few degrees above freezing.
This leads me to believe that a palms hardiness should be
assessed by whether it can survive a British/European winter or
not, and not purely by the figure of a minimum temperature.
I have lost many small palms due, I believe, to the lack of any
real heat. I have a polytunnel where I try to prevent temperatures
dropping more than a couple of degrees below 0, and a small greenhouse,
where I keep my more tender palms frost free, though even here losses
have been high. Although it can be disheartening to have these losses,
I believe that I have learned a lot by experimenting in this way.
For instance, Ive learned that seed provenance can play a
big part when trying new species. I have tried out many Copernicia
seedlings this year, species including C. alba and C. prunifera,
many of which have succumbed to the low winter temperatures. However,
I managed to obtain seed of Copernica macroglossa from the US from
a parent that gets a regular frosting, sometimes as low as -7°C!!!
Needless to say, I havent lost a single seedling (yet) and
Ive allowed them to get frosted to -2°C. Watering is another
area that needs to be observed as well. I tend to keep my palms
very dry during the winter and water with a fungicide solution about
once a month just to keep any root rot in check; its amazing
how a little moisture and cold temperatures can rot some palm roots
in no time.
Other palms that have taken -2°C with little
or no damage include Wallichia disticha and densiflora, Wodyetia
bifurcata, Parajubaea cocoides, Dypsis decipiens, and Chamaedoria
seifrizii and C. oblongata. Happily the garden and unprotected old
favourites are doing well. Phoenix canariensis, Rhapis excelsa,
Brahea armata, Brahea edulis, Trithrinax acanthocoma, and Washingtonia
robusta and filifera have all come through our lowest night of -4°C
so far without being scathed, although Livistona chinensis suffered
slight tip burn. I was also shocked to find that same following
morning that my heater had failed in the polytunnel. There was ice
everywhere, which was soon defrosted by the fiery language that
followed, of which I couldnt possibly repeat in a family magazine
like this one. Ravenea rivularis and Coccothrinax barbadensis had
been totally destroyed, with most of the leaves being lost to the
low temperature. However, I think they will recover as the new spears
seem to have remained intact. Howea forsteriana had suffered about
20% tip burn. It took me the following weekend to sift through the
debris, but to my surprise I didnt lose a single palm, and
a few weeks later, they still seem to be alive. All the other palms
have come through OK. Caryota himalaya is actually growing, if very
slowly; Syagrus romanzoffiana and Livistona Saribus look great,
although they did sustain some damage; Phoenix roebelenii and P.
theophrasti are untouched; as are Rhopalostylis sapida, Chamaedorea
microspadix and C. radicalis, and an X Butiagrus hybrid.