Are these the northernmost outdoor palms on Earth?

[Nafnlaus]

Reykjavík, Iceland - ALDIN Biodome Research Garden, 64,1˚N

I didn't see fit to comment until they had survived a winter, but the first two I've uncovered apparently have, so I figured it's time to ask!  

Trachycarpus fortunei: wasn't in great shape when I got it last spring; had partly recovered by the fall, but experienced complete outer leaf dieback over the winner. Inner leaves however remain green; the exact cutoff point between dead and alive leaves is yet to be seen.

Trachycarpus sp. nova: I'm in shock. It looks basically just like it did in the autumn. That's one hardy palm

Others of note:

Butia capitata: Still covered.  Will uncover it a week from now.  Fingers crossed!

Various Sabal species: Still covered.  Tiny plants, so I don't have much hope for them; they're basically just one leaf at this point, flat on the ground and lightly covered in wood chips.

Chamerops humilis: Same story, only slightly larger than the Sabals, and buried in a thin layer of pumice.

Trachycarpus wagnerianus: stolen last fall    Who steals a palm tree in Iceland?

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Treatment: All trees are planted in beds that have PEX tubing buried in them.  ~28,5°C geothermal wastewater (the output of home radiators from a nearby neighborhood, which normally would just be discharged into the sea) flows slowly (over the winter, *very* slowly) through the tubing, keeping the soil just over freezing in the winter, and around 18-23°C in the summer (that's hot for us - an average July day is a low of 9°C and a high of 14-15°C).  Trees were imported from THRINAX - Palmengärtnerei und Versand (Jörg is great, I strongly recommend him as a supplier), planted in late spring / early summer, and new leaf growth was visible up through the fall. Over the winter (I think starting in early November?) they were wrapped in trunk protectors, palm bags, and wadded-up waste floating row covers as insulation.

Followup: Once I've assessed fully what's made it, clearly there needs to be followup study.  The wagnerianus should be replaced. If the Sabals and Chamaerops don't make it, larger plants should be tried.  If the Butia does make it, then less hardy species should be tried, to see what the limits are - Jubaea perhaps? And two more 'Nova's should be tried - one with heat but without winter protection, and one without heat but with winter protection. And obviously, the current experiment will need to be continued over many more years.  But I expect the first winter to be the toughest to survive!

Other notes: I kind of regret uncovering them today rather than tomorrow, as the forecast for tonight is -6˚C, but no other temperatures this low are in the forecast for the coming week.  But I think they'll be fine; I left a floating row cover over them for now while they readjust.  I've increased the geothermal water flow to warm the soil up (it's just barely over freezing), and once they've gotten readjusted I'll give them their springtime fertilizer dose. 

[Arecaceus]

Wow that's crazy! As many parts of Iceland are pretty "mild" in winter considering its location I really wonder how are they doing in summer? Especially without longer periods of signifcant warmth. I mean you've got superficial heat from the ground but still the air isn't even close to be warm (for those palms) in summer right?

[Nafnlaus]

17 minutes ago, Hortulanus said:

Wow that's crazy! As many parts of Iceland are pretty "mild" in winter considering its location I really wonder how are they doing in summer? Especially without longer periods of signifcant warmth. I mean you've got superficial heat from the ground but still the air isn't even close to be warm (for those palms) in summer right?

So, we have an extreme example of a "subpolar oceanic climate".  The mean temperature is low (~5°C / 41°F), but there's very little difference between summer and winter. The hottest it's *ever* been was 25,7°C (78,3˚F):

So soil at sufficient depth pretty much everywhere averages about 5°C year-round.

What my research (which won the presidential innovation award last year) revolves around is what we can achieve with soil heating (and what we cannot).  Soil heating greatly increases root activity, but it does basically nothing to, say, protect leaves from frost (except for a very small impact on ground-level leaves).  And while there are disadvantages as well (increases certain pathogens and soil pests love the heat, and too much winter heat can cause plants to break dormancy when they shouldn't), the increased root activity appears to dramatically increase growth, particularly in the spring.  We have tons and tons of spring / early summer sunlight, but the soil is too cold for things to grow quickly (or at all).  So for example fruit trees put on about double the growth per year with soil heating, brassicas yield 2-4x as much, blackcurrent plants increase in volume almost 10x faster, strawberries fruit almost a month earlier, etc.  With cold-sensitive plants, you can often see deficiency signs in unheated beds but no deficiency signs in the heated beds, as the roots function so much better in the heated beds. 

I'm not the first person in Iceland to use geothermal water - there have been various experiments over the years, and a couple farmers use it - but my work is unique in using a low-grade waste product (lukewarm water that normally gets thrown away) rather than (valuable) hot water.  So it makes it much more viable for widespread usage, particularly in-town.  Again, the soil isn't at all getting "hot", it's just being "not as cold as is usual for Iceland"     Palms put their roots down up to a meter or so, and without heating, that soil would be pretty cold year-round.

[Arecaceus]

40 minutes ago, Nafnlaus said:

So, we have an extreme example of a "subpolar oceanic climate".  The mean temperature is low (~5°C / 41°F), but there's very little difference between summer and winter. The hottest it's *ever* been was 25,7°C (78,3˚F):

So soil at sufficient depth pretty much everywhere averages about 5°C year-round.

What my research (which won the presidential innovation award last year) revolves around is what we can achieve with soil heating (and what we cannot).  Soil heating greatly increases root activity, but it does basically nothing to, say, protect leaves from frost (except for a very small impact on ground-level leaves).  And while there are disadvantages as well (increases certain pathogens and soil pests love the heat, and too much winter heat can cause plants to break dormancy when they shouldn't), the increased root activity appears to dramatically increase growth, particularly in the spring.  We have tons and tons of spring / early summer sunlight, but the soil is too cold for things to grow quickly (or at all).  So for example fruit trees put on about double the growth per year with soil heating, brassicas yield 2-4x as much, blackcurrent plants increase in volume almost 10x faster, strawberries fruit almost a month earlier, etc.  With cold-sensitive plants, you can often see deficiency signs in unheated beds but no deficiency signs in the heated beds, as the roots function so much better in the heated beds. 

I'm not the first person in Iceland to use geothermal water - there have been various experiments over the years, and a couple farmers use it - but my work is unique in using a low-grade waste product (lukewarm water that normally gets thrown away) rather than (valuable) hot water.  So it makes it much more viable for widespread usage, particularly in-town.  Again, the soil isn't at all getting "hot", it's just being "not as cold as is usual for Iceland"     Palms put their roots down up to a meter or so, and without heating, that soil would be pretty cold year-round.

Very very interesting! Yes I heard about crops growing in Iceland in greenhouses using geothermal heat. I always wondered how this could be used in cool or colder places as many animals survive winters in subpolar regions with the help of thermal springs. It's very interesting to hear how much ground heat is affecting those kind of palms. I know that some species mostly tropcial or subtropical ones need pretty high soil temperatures to survive or let's say grow year 'round. We had a bad winter here in Western Europe mostly because of the breaking of dormacy followed by cold spells. It was very warm (vegetative temperatures) into early Decemeber then we had a very bad freeze with temperatures sometimes lower than -5°C followed by exceptionally warm weather. Around new year's eve temperatures reached around 20°C some places even higher for a couple of days. This pattern continued just with not so extreme lows but still light frosts and less extreme heat but still exceptionally warm and wet. I don't think I've ever had so many plants looking bad with damages even on the hardiest species. Those fluctuations seem to be harmful to almost any plant. I believe that's also a reason why so many people lose plants during freezes in the Southern United States. They have very warm weather so plants are in growth and without any time to go dormant frost comes through for a week. Palms like Trachycarpus are good growers at lower temperatures I think they might even grow slowly below 15°C? This might be enough in combination with warm soils apperently. Growing palms in Iceland sounds very interesting. And with the warming of our planet I don't even think it's unrealistic to grow the hardies species without protection in a couple of decades. Might become more like Scotland and I'm pretty sure as temperatures here are now exceeding 40°C several times a year which used to be a very rare event or sometimes never even measured Iceland might get 20+°C in summer more frequently. I have seen Trachies being grown in Scotland. Because of the very maritime climate you might have better chances than most of continental Scandinavia, 🌴

[Nafnlaus]

Greenhouses are wonderful - you can grow literally anything in them and have them thrive - but they're also extremely expensive.  This is super-cheap. Anyone with a radiator or a grey water system can do it with their own wastewater, and any city with municipal wastewater or access to any sort of industrial facility or power plant with wastewater.  You actually do them a favour   Wildlife also loves the discharge stream, as it's still warmer than outside temperatures.  PEX is like €1-2 per metre, with tubes about half a meter apart, so basically a couple euros per square metre in material costs - and buried PEX lasts for many decades, so as an amortized cost, it's trivial. With this lukewarm wastewater and mulch or pumice on the surface as insulation, I use 15-20 litres per square meter per day in the winter, and about 80-100l/d/m² in the summer. A single person taking one warm bath per day creates 150-200l of lukewarm water from that on its own.  Radiators create a lot more.

Again, at this point I don't know how they would have fared without (A) winter protection, and (B) soil heating - that'll take more testing. But at least this minimal case has been proven!  My secret dream is, after keeping them alive for a few years and showing that they can thrive, given the right conditions and care, that I could convince Keflavíkurflugvöllur (the main international airport) to plant palm trees outside to confuse the heck out of tourists 

[Arecaceus]

23 minutes ago, Nafnlaus said:

Greenhouses are wonderful - you can grow literally anything in them and have them thrive - but they're also extremely expensive.  This is super-cheap. Anyone with a radiator or a grey water system can do it with their own wastewater, and any city with municipal wastewater or access to any sort of industrial facility or power plant with wastewater.  You actually do them a favour   Wildlife also loves the discharge stream, as it's still warmer than outside temperatures.  PEX is like €1-2 per metre, with tubes about half a meter apart, so basically a couple euros per square metre in material costs - and buried PEX lasts for many decades, so as an amortized cost, it's trivial. With this lukewarm wastewater and mulch or pumice on the surface as insulation, I use 15-20 litres per square meter per day in the winter, and about 80-100l/d/m² in the summer. A single person taking one warm bath per day creates 150-200l of lukewarm water from that on its own.  Radiators create a lot more.

Again, at this point I don't know how they would have fared without (A) winter protection, and (B) soil heating - that'll take more testing. But at least this minimal case has been proven!  My secret dream is, after keeping them alive for a few years and showing that they can thrive, given the right conditions and care, that I could convince Keflavíkurflugvöllur (the main international airport) to plant palm trees outside to confuse the heck out of tourists 

Sounds like something out of Cities Skylines 😂 (I don't know if you know that game). Cool plan but as I said I don't think it's too unrealistic long term with the climate getting warmer. 😏