Soil Temperatures

[SailorBold]

I was wondering if anyone recently checked their soil temperatures. Since I have landscaped my yard I have been gaining interest and routinely monitoring using a wireless meat thermometer. During the daytime I have been monitoring the surface temperature as well using a scanning IR thermometer.

Our high temperature today in ABQ was 96f and the weather sunny. I scanned three areas of my front yard facing south around 3pm, and attained readings at 158f, 164f, and 173f.

I am writing this just after 10pm local time and my wireless meat thermometer shows the soil temperature at 94f.

How important of a factor is this in palm cultivation...? I know the importance in relation to agriculture but has anyone ever studied in detail how important it is to evergreens? For instance.. winter hardiness...water pressures within palms during cold snaps and say... variability in cold damage to palms during prolonged or quick cold snaps. Could this be a key factor...

[SailorBold]

I took this soil temperature map off of GreenCast website for references.

Edited September 1, 2014 by SailorBold

[Jim in Los Altos]

I can't relate to your soil temps because mine could never reach those levels given that, even on a 90F day, late night temps would be in the 60s. I monitor my soil temperatures regularly throughout the year and right now, most of my yard measures 73F to 77F with the exception of soil near heat catches like concrete driveway and stone walkways and patios where their heating has brought soil temps 6" below the surface and a few inches away from said hardscaping to as high as 93F in mid afternoon.

The main concern I have is with winter soil temperatures and marginal tropicals and concern with root rot. If the soil is wet and cold enough to put a halt to any appreciable growth, rot can occur and make it harder for the palm or other plant to prosper in the spring. in January, my soil temperatures on average can drop to the 50s with a few exceptions where I have warmer soil closer to my house. This is what would outright kill a coconut palm or many true tropicals. I have identified the warmest soil areas in my yard and have planted tender palms in those areas with some decent success.

[Moose]

Those temps seem excessive. Mulching would lower those surface temps in the summer, warming the soil surface in the winter.

[SailorBold]

For information.. today the soil temperature was 84f a little after 7am and our low 62f.

[SailorBold]

Interesting Jim... I am sure there are numerous studies on this...however I will add 'unsupported thought' by looking at the plant as a system..and to open discussion.

Well obviously palm trees have a growing point...what we call a 'bud'. this is the area where most of the water and nutrients from the root system are transported to... leaves.. emerging spears... Now fatal damage or even superficial damage is one thing... for the sake of discussion...this area of the plant is constantly being replenished with good ole H2O.

We have seen that once this system is 'cut-off' the leaves wilt and wither essentially drying up... similar to your example of 'cold and wet' and 'root rot' in the relation to tropical plant requirements... pulling weeds does this too.

I'm theorizing if the water coming from the root is warm... than the bud must be warmer too essentially increasing cold hardiness...

I'm sure climate plays a role also.. but I'm suspecting the effect is similar to even temperate palms.

You mention Coconut Palms.. so what if you built a large heated planter.. and grew a coconut AND you are mostly frost free.... why wouldn't that work? If energy would be an issue.. use a solar panel..

Are you ready for a new challenge Jim? I need you to test my theory.

Plug-in Pot are the wave of the future....

Moose- while my landscaping condition is new... the only adverse reaction I have seen is when I neglected watering. I use a automatic drip system... but not everything is on that system as I add more plants to the landscape.. also I don't have 'bare soil' I will add that I use weed fabric with a 2 to 3" layer of crusher-fine rock.

I would argue that mulching would have an opposite effect in winter.. although I don't have information to back that up.

Edited September 1, 2014 by SailorBold

[Jim in Los Altos]

Jimmy, The problem with Cocos for instance is that the growing point growth grinds to a halt with air temperatures at 60F or so regardless of how warm the soil may be. Any water transported to the growing point has plenty of time to cool to air temperature before reaching the bud. That's if there is much or any water movement at all in cold and damp weather. Cocos here would need heated soil and a heated enclosure for much of the winter here. I've coaxed a coconut to live for three years by simply protecting it from frost and situating it in the warmest part of my yard but it was a sad looking plant regardless of whether it was alive or not.

[Moose]

Interesting Jim... I am sure there are numerous studies on this...however I will add 'unsupported thought' by looking at the plant as a system..and to open discussion.

Well obviously palm trees have a growing point...what we call a 'bud'. this is the area where most of the water and nutrients from the root system are transported to... leaves.. emerging spears... Now fatal damage or even superficial damage is one thing... for the sake of discussion...this area of the plant is constantly being replenished with good ole H2O.

We have seen that once this system is 'cut-off' the leaves wilt and wither essentially drying up... similar to your example of 'cold and wet' and 'root rot' in the relation to tropical plant requirements... pulling weeds does this too.

I'm theorizing if the water coming from the root is warm... than the bud must be warmer too essentially increasing cold hardiness...

I'm sure climate plays a role also.. but I'm suspecting the effect is similar to even temperate palms.

You mention Coconut Palms.. so what if you built a large heated planter.. and grew a coconut AND you are mostly frost free.... why wouldn't that work? If energy would be an issue.. use a solar panel..

Are you ready for a new challenge Jim? I need you to test my theory.

Plug-in Pot are the wave of the future....

Moose- while my landscaping condition is new... the only adverse reaction I have seen is when I neglected watering. I use a automatic drip system... but not everything is on that system as I add more plants to the landscape.. also I don't have 'bare soil' I will add that I use weed fabric with a 2 to 3" layer of crusher-fine rock.

I would argue that mulching would have an opposite effect in winter.. although I don't have information to back that up.

Mulch acts as an insulator. The air pockets in it function much like a blanket. Also slows down the evaporation of water. I've walked outside barefoot during cold fronts to stand on the mulch. My hooves could definitely feel the difference in temperature.

[SailorBold]

Jim.. Heh heh.. I'm joking mostly...That's why I find this interesting..I have no experience with Cocos or actually many palms that need or grow in more tropical conditions..mainly well because they will never have a chance in my climate; but from an observational perspective, I have that curiosity to understand if there is... if any correlation.. to soil temp and air temp in regard to palm growth... or generally species specific growth...during the growing seasons in mine and different climates.

This spring I was amazed when my Desert Willow leafed out 6 weeks ahead of others in my area. It was very noticeable. While my soil is warmer with my aggregate choice.. the air temperature as far as low temps are concerned are essentially the same. The heat radiating off of my substrate during the day is another factor.. however I haven't pin pointed the exact reason why it leafed out so early. Something changed its internal clock.

My palm plantings are new and while I did not document winter growth.. I know it occurred on my Butia and Washingtonia... even with freezing morning temperatures.

Its fascinating.

Edited September 1, 2014 by SailorBold

[SailorBold]

Moose.. Interesting also.. In my area the experts suggest using mulch (makes sense really)... I suppose I thought it was for moisture retention and water conservation. I never thought of temperature regulation..

Now that you mention it... I do recall seeing frosty mulch.... now I'm not saying it is not a good temperature insulator. We have many freezes in my area during winter and many frosts too- but frost is less common.. mainly due to radiational cooling.. say on car windshields.. metal surfaces.... but not on plants. I'm not saying it doesn't happen because it frosts every year.. The air is dry and dew points often lower than low air temperatures.

That supports your observation. Ice crystals indicate fast heat release... even at surface it must keep the root area warmer underneath the protective mulch.

EUREKA.

[JEFF IN MODESTO]

I keep a digi thermometer in the ground .

Our average air temps have been 95f/65f the past three months.

In My heavily mulched soil , at 6in depth the soil temp is generally around 72f in the morning and 80f in the pm.

[tropicbreeze]

At what depth are you taking the temperature readings? There's a big difference in temperatures on a thermometer laying on the ground in the sun to just below the soil surface and even a metre above the soil surface.

[Mauna Kea Cloudforest]

My brahea garden is landscaped with lots of rock, and it's West facing with complete wind protection. The temperature on the ground gets so hot (easily 120F or more) that it killed several plants that were meant for cool climates. I've replaced everything with heat lovers.

[SailorBold]

Tropicbreeze- The thermometer is roughly over 6 inches in length.. placed directly into ground pierced through weed fabric underneath 2+ inches of crusherfine gravel. It is wireless and I can monitor the temp from inside my house.

Reading taken this afternoon at 550pm local time: 98f

High temp was 94f

BraheaAxel: That's about the temperature I see on my driveway using a scanning IR thermometer. It retains heat also but doesn't hold it like the ground does.... at least the surface. I have read anywhere from 120-150f on white pavement during a summer day.

[Axel Amsterdam]

With regards to the effect of soil temps for actual palm growth i did the following experiment (in Amsterdam Holland):

I warmed the soil around my queenpalm by drenching it with warm water (around 90f for around 10 minutes) a couple of times a week during periods of very cool weather (in which the queen nornally didnt grow, i marked the spear). There was absolutely no effect. Growth kept stalled.

Later I wrapped the trunk of the same queen in thick plastic with heating cables inside without covering the soil. During the same cool weathertype growth started immediately after the first night. It kept growing throughout the entire winter, pushing a large spear also during nights (significantly) below 32f.

For me this lead me to the conclusion that a queen is mainly depending on air temps, especially nighttemps, and not so much on soiltemps (if any).

Warm soil probably leads to more rapid rootforming so will perhaps add to more growth in the long term.

Edited September 2, 2014 by Axel Amsterdam

[tropicbreeze]

Tropicbreeze- The thermometer is roughly over 6 inches in length.. placed directly into ground pierced through weed fabric underneath 2+ inches of crusherfine gravel. It is wireless and I can monitor the temp from inside my house.

Now see what you've done! I'm buying a scanning IR thermometer and a soil probe thermometer. The things you do to "keep up with the Joneses". Spring started 2 days ago, so will be interesting to see the temp figures progressing.

[Daniel]

With regards to the effect of soil temps for actual palm growth i did the following experiment (in Amsterdam Holland):

I warmed the soil around my queenpalm by drenching it with warm water (around 90f for around 10 minutes) a couple of times a week during periods of very cool weather (in which the queen nornally didnt grow, i marked the spear). There was absolutely no effect. Growth kept stalled.

Later I wrapped the trunk of the same queen in thick plastic with heating cables inside without covering the soil. During the same cool weathertype growth started immediately after the first night. It kept growing throughout the entire winter, pushing a large spear also during nights (significantly) below 32f.

For me this lead me to the conclusion that a queen is mainly depending on air temps, especially nighttemps, and not so much on soiltemps (if any).

Warm soil probably leads to more rapid rootforming so will perhaps add to more growth in the long term.

Axel, from my experiments with heat cables and cold hardy palms I have also noticed that the temperature of the growing point is the critical factor to increased growth rates. However some Sabals don't fit this rule and it is the soil temperature that is important factor.

Also in Winter I believe it is better to warm the soil with warm water so that roots do not get too cold and rot.This will have little effect on immediate growth but may reduce Winter set back.

Edited September 2, 2014 by Daniel

[Moose]

With regards to the effect of soil temps for actual palm growth i did the following experiment (in Amsterdam Holland):

I warmed the soil around my queenpalm by drenching it with warm water (around 90f for around 10 minutes) a couple of times a week during periods of very cool weather (in which the queen nornally didnt grow, i marked the spear). There was absolutely no effect. Growth kept stalled.

Later I wrapped the trunk of the same queen in thick plastic with heating cables inside without covering the soil. During the same cool weathertype growth started immediately after the first night. It kept growing throughout the entire winter, pushing a large spear also during nights (significantly) below 32f.

For me this lead me to the conclusion that a queen is mainly depending on air temps, especially nighttemps, and not so much on soiltemps (if any).

Warm soil probably leads to more rapid rootforming so will perhaps add to more growth in the long term.

Axel, from my experiments with heat cables and cold hardy palms I have also noticed that the temperature of the growing point (meristem) is the critical factor to increased growth rates. However some Sabals don't fit this rule and it is the soil temperature that is important factor.

Also in Winter I believe it is better to warm the soil with warm water so that roots do not get too cold and rot.This will have little effect on immediate growth but may reduce Winter set back.

[SailorBold]

Well tropical moisture from Odile was a total bust. My rain gauge totaled .30" of moisture. Funny thing is- I heard from the weather guys that we would see anywhere from 1 to 6 inches.

The sun was out and the high was 88F (31C)..

For info.. my soil temp this evening was 91F (33C) just before 10p local time.

[tropicbreeze]

These are surface temperatures taken with IR thermometer at around 2:30 pm today, clear sunny day and moderate gusty wind, still early spring here.

Ambient temp 39C (102.2F)

Bare soil in sun most of day up to 2:30 PM 73.5C (164.3F)

Pandanus leaf in sun from about midday 58.9C (138.0F)

Ptychosperma macarthuri leaflet in shade all day 41.2C (106.2F)

Mango leaf in sun from early morning 53.1C (127.6F)

I still haven't got my soil probe thermometer, so all surface measurements at this stage.

[SailorBold]

Pretty interesting.. I never thought of checking leaf temperature.

Plants can take a lot of heat apparently.

[Bill H2DB]

Here is a link to the FAWN site , ( Florida ) http://fawn.ifas.ufl.edu/

Arrow over a station for data . Soil temp is given at -10 cm .

During the winter there is quite a range from S Fla to the panhandle .

IR guns read only the surface. I work for an engineering company , and in checking soils , piles

of dirt , loads of hot asphalt etc , they differ greatly from probes actually in the mass .

Great for quickly find variations in a mass though .

[tropicbreeze]

I always imagined plants could cop intense heat being out in the sun but never had a way to make actual measurements. Also, it seems they can do it better in high humidity conditions. That's why you see some plants looking good in high temperature/high humidity situations and the same plants badly burned at lower temperatures but very low humidity.

Although it's early spring now, our sun gets overhead just after the middle of spring (28th October), hence the earlier intensity. Throughout Nov-Dec it's lowering, and then returns on its way back north causing another peak. But the second peak doesn't feel so bad because humidity is higher and there's more chance of cloud cover/rain.

[SailorBold]

The weather is cooling here significantly at night. The temperature today was 80F(27C)/ 42F(6C).

For reference.. at 11:15pm my soil temp at 5" depth was 78F(26C).

[Jim in Los Altos]

It's warm here still. We hit 84F this afternoon and right now at midnight, it's 62F. My soil temperatures are running between 68F in the coolest spot to 75F in the warmest recorded at 5PM. I'm still getting phenomenal growth on my marginals and we're expecting around an inch of rain this weekend with mild temps. This is happy palm weather.

[SailorBold]

For reference- the local weather today was mostly cloudy with a high temp at 52F(11C) and a low at 32F (0C).

Soil temperature just after 9pm local time is 59F(15C).

I guess a question would be.. as far as root growth and palms.. at what temperature does root growth stop/start?

[Pando]

Jim, what's the coldest temperature you've ever recorded in your yard?

[smithgn]

Thought I'd chime in on this thread...

As far as greenhouses go, if the air temperature inside my greenhouse drops into the 50's and the soil of my palms inside the greenhouse stays at 70-80 degrees, are my plants still going to grow? I'm still trying to calibrate my greenhouse and get it to stay at a constant temperature but im technologically limited at the moment.

[SailorBold]

smithgn- Im guessing yes.. although that is a world away from me.. cold frame and hot house I have no experience with either.

[smithgn]

Thanks. Yeah, I've been doing a whole bunch of research these last few months. The toughest thing right now is keeping my plants from frying to a crisp. When the sun starts hitting my greenhouse it gets upward of 100 degrees. But luckily, for not very long.

[SailorBold]

I just replaced the batteries... 930 pm local time. Currently 31f (0C)... Soil temp is 55f.

It will be interesting if my Bougainvillea returns from its roots, at least that's one of the things I'm hoping for. Shrugs

smithgn- do you have an exhaust set-up?

[tropicbreeze]

Took these measurements at 07:30 am this morning before the sun came through.

Air 2 metres above ground surface:
Temp 26.4C (79.5F)
RH 91%

Soil surface 28.6C (83.5F)

Soil 150mm depth:
Temp 30.4C (86.7F)
RH 99%

No rain overnight, rain yesterday 2mm, day before 3mm.

[Jim in Los Altos]

Jim, what's the coldest temperature you've ever recorded in your yard?

Pando, Sorry for not noticing you post until now. The lowest temperature in the last fifteen years I've recorded is 26F in 2007. Historically, it's been colder. The records for Los Altos show a 22F reading in 1990 as the all time record. Since 2007 I have had a string of years where the lowest was 32F and one where it dipped briefly to 29F. This season's low up to now is 46F but we're entering a cooling period and will likely see 40F for a few nights and, perhaps, an upper 30s reading for a couple of nights.

[smithgn]

I don't have an exhaust type set-up. I have a real simple greenhouse made by Flower houses. It's made for flowers I suppose, but still works fine with the palms I have in there. I can definitely see myself investing in a much larger and elaborate greenhouse than I have now.

[Pando]

Thanks Jim so much. You actually already answered the same question I asked in another thread...

Do you think your thicker foliage/canopy will help significantly if it ever gets to these lows again, and how will you protect your tender stuff? Cover them, hang lights, wrap them, tent them, and/or use an outdoor radiant gas heater? I also have a couple of marginal species in my yard that I will need to protect in the coldest of nights, so I'm trying to prepare.

[Jim in Los Altos]

Thanks Jim so much. You actually already answered the same question I asked in another thread...

Do you think your thicker foliage/canopy will help significantly if it ever gets to these lows again, and how will you protect your tender stuff? Cover them, hang lights, wrap them, tent them, and/or use an outdoor radiant gas heater? I also have a couple of marginal species in my yard that I will need to protect in the coldest of nights, so I'm trying to prepare.

I rarely do anything special to protect anything in my yard. I'll make an exception for my Lemeurophoenix since it's actively growing still and we're going into a chilly period. It will get a cover as long as the low temperatures are forecast to go into the upper 30s. My garden is otherwise dense so it tends to create its own protective barrier to the more tender stuff. Soil temperatures are higher than usual right now, which will help moderate the colder air moving in over us the next several days.

[SailorBold]

Took these measurements at 07:30 am this morning before the sun came through.

Air 2 metres above ground surface:

Temp 26.4C (79.5F)

RH 91%

Soil surface 28.6C (83.5F)

Soil 150mm depth:

Temp 30.4C (86.7F)

RH 99%

No rain overnight, rain yesterday 2mm, day before 3mm.

Interesting. Are you taking your measurements in a 'full sun' location? I guess that well obviously would be a noted variable to consider. All of my measurements have been in southern exposure full sun- and without 'canopy' so I will add that. How have your daytime temps been?

I am limited in my palm choices due to this.. aside from sun requirements for certain species; the only palms that would be able to survive the cold here in a northern exposure planting would be Trachycarpus species which I have seen.. perhaps needle palm (which is rare here) and other types. I have never tried to plant any palms on the north side of my house.. but I suspect this will change. Eastern and western sites would also have their nuances but again I haven't looked into soil temperatures there either Perhaps some southerly shaded areas could be interesting due to the sun they might receive in winter versus summer.. maybe a shade plant might be able to take winter but not summer sun? Do they teach this stuff????

I pretty much eyeball where snow stays the longest... but 30C (87F) seems warmer than a shaded location in my limited experience.

I don't have an exhaust type set-up. I have a real simple greenhouse made by Flower houses. It's made for flowers I suppose, but still works fine with the palms I have in there. I can definitely see myself investing in a much larger and elaborate greenhouse than I have now.

Me too! Harbor freight looks to have fairly inexpensive kits.. or perhaps you can build your own. I haven't jumped into that nest yet.. but I could see myself investing in one even as a hobbyist.

We received a half inch of snow overnight.. its gone now but was nice.

The low was 29F (-1.6C). My soil temp is 47F (8C).

[Jim in Los Altos]

I took these pictures a noon today, Dec. 26. The first is in the coolest part of my yard, the second, is typical of most of my yard and the third explains why my Lemeurophoenix is growing in this warm area above a sewer line. I expect some lowering of all these numbers as we endure this chilly spell.

[tropicbreeze]

Interesting. Are you taking your measurements in a 'full sun' location? I guess that well obviously would be a noted variable to consider. All of my measurements have been in southern exposure full sun- and without 'canopy' so I will add that. How have your daytime temps been?

I am limited in my palm choices due to this.. aside from sun requirements for certain species; the only palms that would be able to survive the cold here in a northern exposure planting would be Trachycarpus species which I have seen.. perhaps needle palm (which is rare here) and other types. I have never tried to plant any palms on the north side of my house.. but I suspect this will change. Eastern and western sites would also have their nuances but again I haven't looked into soil temperatures there either Perhaps some southerly shaded areas could be interesting due to the sun they might receive in winter versus summer.. maybe a shade plant might be able to take winter but not summer sun? Do they teach this stuff????

I pretty much eyeball where snow stays the longest... but 30C (87F) seems warmer than a shaded location in my limited experience.

Those readings were before the sun was up, but from about 08:30 - 09:00 that spot's in full sun for the rest of the day (apart from any cloud cover). Took readings again 16:00 the same day. There was 2.5mm rain around midday then sun for the rest of the day and occasional hazy cloud.

Air 2 metres above ground surface:

Temp 33.0C (91.4F)

RH 68%

Soil surface 42.6C (108.7F)

Soil 150mm depth:

Temp 37.1C (98.8F)

RH 99%

Average daily maximum for December has been 35.8C (96.4F). And it's drier than normal, have got 38.1% of average December rain with only 5 days to the end of the month. We don't get a lot of temperature variation, the most is in the dry season (winter) when we can get about 18C differences. The least variation is a couple of degrees in the wet season when there's cyclones around (also our coldest days) when day/night temperatures are something like 24C (75.2F) to 26 (78.8F).

[BS Man about Palms]

Jim, how deep does that soil probe go?