Insomniacs Take Note: This is an interesting post and as such will probably not take you to blessed slumber. You may be here because you peruse my postings looking for sleep inducing material. I recommend instead the posting “A Tale of Two Emails” and as usual, good luck to you.
Every 5 years or so the temperature here in Washington goes below 5F. Temperatures this low present an existential threat to my Chinese windmill palm trees, which are generally thriving here at latitude 39.0N in Bethesda MD. Two are about 5 ft tall, and one is much taller at about 15ft. I can’t explain the difference in heights. They were planted at the same time.
Here are a few pictures of these palms. Snow doesn’t faze them. The temperature just has to always be above 5F.
When they were smaller, I would throw a 20×20 tarp over each one and put a light bulb under the tarp by the trunk. The bulb provided enough warmth to keep the temp under the tarp above 5F. That doesn’t work for a 15ft palm tree. A 40×40 tarp would work but is unmanagable even with two people and almost impossible to get over the top of the tree. And a 100 watt light bulb wouldn’t be enough to keep it warm.
I spent some time thinking about how to get the tarp over the tree when I had an epiphany. I didn’t need to cover the top of the tree. All I needed to do was cover the trunk firmly with tarp right up to the lowest fronds and put a heater in the tarp. The protrusions from cut fronds prevent the tarp from actually hugging the trunk, which worked in my favor because it lets the heat go up (read on). I bell-bottomed the tarp near the ground so it formed a skirt that I sealed to the soil with paving bricks. Then I put a fan driven 600 watt ceramic heater inside the skirt. Yes, the heater says not to use it outside. I did anyway, knowing there would be no moisture that might short it. And I put the heater on a paver brick so it was level and not touching any ground cover.
Here are the pics…
See photo below. That’s where I put the heater.
And the picture below shows the cut frond stubs that keep the tarp from hugging the trunk and allow hot air to move up.
It works as follows: Inside the tarp, the ceramic heater puts out a steady stream of hot air. This air has nowhere to go inside the tarp but up, and escapes where the fronds begin at the top of the plant. The warm air coming out the top keeps the top leaves and most importantly the sensitive core (where new shoots emerge) above 5F.
It seems to have worked. The trunk felt toasty warm when I stuck my hand thru the tarp openings. I could feel the relatively warm air come out the top. The palm tree is still alive one week after two nights around 5F and the two days in-between and after at around 20F (-6C). That’s 2 full days of hard frost temperatures. Five degrees is acknowledged as being literally the “drop-dead” point below which survival of these cold hardy palms is not assured. And if the temperature drops below 0F (-17C) most unprotected Chinese Windmill palms will die.
If you have tall Chinese Windmills growing at high latitudes, consider protecting them this way during the next hard frost. It’s a lot easier than wrapping the upper fronds in tarp.
UPDATE: July 1, 2014. My three palms have kicked the proverbial bucket. The polar vortex in February killed them. They are now in Windmill Palm heaven, where it’s always sunny and warm. My valiant, heroic, expensive and time-consuming efforts were all for naught. All that’s left are the dead trunks, still standing. I’m not going to post any pics. That would be like taking pictures of dead relatives in their coffins.
If you’re wondering how I’m holding up, I’m past my mourning period and am getting on with my life. A support group would have helped but I couldn’t find one that dealt with this particular situation. In case you’re wondering if my suggestions regarding cold weather care for palms are still valid, I would have to say no.