thermal mass Impact of Common Landscape Materials

[kinzyjr]

Overview

The purpose of this thread is to record observations of surface temperatures and their change over time under various conditions for common landscape materials.  Most of us would assume that the borders and other materials we use to landscape our yards are relatively close in heat capacity, with albedo having an impact for the darker materials.  This falls in line with the interest in urban heat islands (UHI), since having some of these materials near small plants may give them a boost overnight if they can hold enough heat.  Landscapes with a lot of hardscaping may be able to gain a small advantage, especially if the grower is able to cover the plant in a way that traps the heat stored by the hardscape.

First recording: Surface temperatures over time on a late summer night.

On September 6th, 2023, the high temperature in the yard reached 97F and the low that morning reached 71F.  This was a sunny day with little cloud cover.  There was no rain and very light wind throughout the day.  Surface temperatures were recorded for various garden borders from 6PM through 10:30PM. 

[flplantguy]

I'm very excited to see how this goes!  I'm not even close to placing my own landscape so I can test things yet, so if you do the hard work for me in advance that's awesome😃.  I think I'm going to need every advantage I can get too.  I found some research about heat capacity of certain mineral types too, for when I do a permanent layer of rock on the driveway where the shell is now.  I'll see if I can find it.

[kinzyjr]

6 hours ago, flplantguy said:

I'm very excited to see how this goes!  I'm not even close to placing my own landscape so I can test things yet, so if you do the hard work for me in advance that's awesome😃.  I think I'm going to need every advantage I can get too.  I found some research about heat capacity of certain mineral types too, for when I do a permanent layer of rock on the driveway where the shell is now.  I'll see if I can find it.

The big factors for each of these things are albedo, heat capacity, conductivity, and mass.  The ideal material has a high albedo, high heat capacity, good conductivity, and a lot of mass.  A giant dark slab of concrete is the next best thing to water due to water's incredible heat capacity.  These are things you and most of the other posters already know.

As far as testing each of the materials goes, a few things have jumped out so far:

• The landscape materials that absorb and retain the least heat out of everything in the yard are the Alameda edgers and Scalloped edging.
  • This may be due to the way they are poured or the type of concrete used.
  • The Matt Log Edging is slightly better, especially if painted black to increase albedo.
• Retaining wall blocks and step stones seem to work well.
  • There's not a significant difference between red and black step stones.
  • There is a difference if you take a standard step stone and paint the top black.
• Large chunks of concrete work fairly well, but not as well as a solid slab due to thermal mass and conductivity.
  • A solid 18 in x 18 in block doesn't work as well as a sidewalk.
• Pavers or Step pads pressed into a concrete slab work really well.
  • I think the increased albedo of a darker paver combined with the high heat capacity and mass of a thick concrete slab are a good marriage.
  • My former patio and pool area was a solid concrete slab with pavers pressed into it adjoining a swimming pool.  It did mute radiational cooling pretty well.
  • Probably the best example of pavers and bricks pressed into concrete and adjoining asphalt creating a microclimate is ICON Park in Orlando - home of the I-Drive coconut.

Keep in mind there is a limited amount of impact any of these components can have in common quantities.  The heat island effect of cities is due to a very large thermal mass that is difficult and often infeasible to reproduce in a landscape.  That said, the effect seems to start at a lower threshold than what was once thought.  Lakeland hasn't eclipsed 200,000 people yet, but look at the impact during last year's early season "cold front":

[flplantguy]

I watch those fronts a lot to see where the warmest spots are.  My hope is the inland development near me, and the current industrial and commercial corridor i border, will add latent heat nearby and block cold from building up.  Between that and my landscaping I'm hoping I block a lot of the coldest air on those few freeze nights without it being as intense an effect as a large city.  Just stopping frost like in pinellas county would be awesome.

[kinzyjr]

Second Recording: Surface temperatures over an early season cold front. 

The goal here was to find the materials that managed to finish the overnight hours above ambient air temperature as well as identify anything that could be forcing a negative transfer of heat from the air to the item in question.  The air temperature at the top was recorded over a mulched area in one of the coconut beds.  This temperature sensor was chosen because it has been the most consistent overnight and during the day since the sun can't hit it directly.

The orange boxes are surface temperatures that are at least 3F warmer than the current air temperature.  The green boxes are surface temperatures up to 2.9F greater than the air temperature.  The blue boxes are temperatures that are lower than ambient air temperature, which is less desirable in this instance.

The items starting from Concrete Near AMB and finishing at Patio Slab - Maypan do not receive late afternoon sun since they are in the backyard.  The items starting at Black Block and finishing near Retaining Wall - Front are in the front yard and receive sunlight until it is blocked by a tree or the sun completely sets.

The ground temperature was taken by scanning the surface of the front yard and is not a soil temperature.

Winners:

Patio Slab - Maypan: The slab under my patio is roughly 18 inches thick.  This summer, I painted the exposed surfaces Dark Kettle Black.  Dark surfaces tend to both absorb and discharge their heat energy quicker than lighter surfaces.  Overnight it had a drop of less than 20F and finished more than 7F above ambient air temperature.

Sidewalk - Near Brick: The sidewalk wrapping around the south and west sides of the house and through the Atlantic Tall coconut bed finished a close second to the patio slab, showing that the overall contiguous mass of concrete wins out regardless of surface color.

Black Block: This dense landscaping block was probably meant to be a base of a birdbath or fountain.  It is very heavy and was painted black for this test.  Approximate dimensions are about 16inx16inx8in.  It discharged its heat fast as expected, but was able to store enough to finish more than 5F above ambient air temperature.

Street: No surprise here that a long asphalt street stores enough heat to finish the night with room to spare.

Black Pad in Concrete: There are a series of six 12in step pads with the tops painted black embedded in a small concrete slab I poured to eliminate a weedy area.  It managed to finish the night at just over 3F higher than ambient air temperature.  The black pad in the front without the benefit of a slab to transfer heat into for storage managed to come up roughly even, but that's with at least another 3 hours of sun exposure.

Red Step Pad: In both the front and back, they managed to at least come up a little above ambient air temperature, making them a good hardscaping option for a path.  Embedded in a concrete slab, they would potentially come up a little stronger since these are all on their own.

Middle of the Pack:

Clay Bricks (Red and Brown): These are supposed to have the same heat capacity as concrete, but even a large pile of both doesn't stack up to a poured slab.  The did finish a smidge higher than ambient air temperature, but for the amount of mass in the stack...

Step Pad - Maypan: This is a different type of step pad that looks more like coral than stone.  It did OK, especially considering it gets the least sun.

Losers:

Alameda Edgers: These routinely finish below ambient air temperature.

Scalloped Edging: Painting them black significantly helps them store heat, but they discharge it very quickly due to their low mass.

Black Concrete Pillar: This one was a surprise since they seem to have a pretty large mass.

Small chunks of Concrete: They need more mass in order not to discharge all of the heat they store.

Inconclusive:

Retaining Wall Blocks: One in front performed rather well, while the one near the Maypan discharged its heat completely.

Black Curb Concrete: It stored a lot of heat and discharged it pretty fast.  While it ended up lower than ambient air temperature at 6am, it did start off at 125F.

[D. Morrowii]

5 minutes ago, kinzyjr said:

Second Recording: Surface temperatures over an early season cold front. 

The goal here was to find the materials that managed to finish the overnight hours above ambient air temperature as well as identify anything that could be forcing a negative transfer of heat from the air to the item in question.  The air temperature at the top was recorded over a mulched area in one of the coconut beds.  This temperature sensor was chosen because it has been the most consistent overnight and during the day since the sun can't hit it directly.

The orange boxes are surface temperatures that are at least 3F warmer than the current air temperature.  The green boxes are surface temperatures up to 2.9F greater than the air temperature.  The blue boxes are temperatures that are lower than ambient air temperature, which is less desirable in this instance.

The items starting from Concrete Near AMB and finishing at Patio Slab - Maypan do not receive late afternoon sun since they are in the backyard.  The items starting at Black Block and finishing near Retaining Wall - Front are in the front yard and receive sunlight until it is blocked by a tree or the sun completely sets.

The ground temperature was taken by scanning the surface of the front yard and is not a soil temperature.

Winners:

Patio Slab - Maypan: The slab under my patio is roughly 18 inches thick.  This summer, I painted the exposed surfaces Dark Kettle Black.  Dark surfaces tend to both absorb and discharge their heat energy quicker than lighter surfaces.  Overnight it had a drop of less than 20F and finished more than 7F above ambient air temperature.

Sidewalk - Near Brick: The sidewalk wrapping around the south and west sides of the house and through the Atlantic Tall coconut bed finished a close second to the patio slab, showing that the overall contiguous mass of concrete wins out regardless of surface color.

Black Block: This dense landscaping block was probably meant to be a base of a birdbath or fountain.  It is very heavy and was painted black for this test.  Approximate dimensions are about 16inx16inx8in.  It discharged its heat fast as expected, but was able to store enough to finish more than 5F above ambient air temperature.

Street: No surprise here that a long asphalt street stores enough heat to finish the night with room to spare.

Black Pad in Concrete: There are a series of six 12in step pads with the tops painted black embedded in a small concrete slab I poured to eliminate a weedy area.  It managed to finish the night at just over 3F higher than ambient air temperature.  The black pad in the front without the benefit of a slab to transfer heat into for storage managed to come up roughly even, but that's with at least another 3 hours of sun exposure.

Red Step Pad: In both the front and back, they managed to at least come up a little above ambient air temperature, making them a good hardscaping option for a path.  Embedded in a concrete slab, they would potentially come up a little stronger since these are all on their own.

Middle of the Pack:

Clay Bricks (Red and Brown): These are supposed to have the same heat capacity as concrete, but even a large pile of both doesn't stack up to a poured slab.  The did finish a smidge higher than ambient air temperature, but for the amount of mass in the stack...

Step Pad - Maypan: This is a different type of step pad that looks more like coral than stone.  It did OK, especially considering it gets the least sun.

Losers:

Alameda Edgers: These routinely finish below ambient air temperature.

Scalloped Edging: Painting them black significantly helps them store heat, but they discharge it very quickly due to their low mass.

Black Concrete Pillar: This one was a surprise since they seem to have a pretty large mass.

Small chunks of Concrete: They need more mass in order not to discharge all of the heat they store.

Inconclusive:

Retaining Wall Blocks: One in front performed rather well, while the one near the Maypan discharged its heat completely.

Black Curb Concrete: It stored a lot of heat and discharged it pretty fast.  While it ended up lower than ambient air temperature at 6am, it did start off at 125F.

Hey this is a pretty cool little study @kinzyjr Honestly I figured the difference between the air and a surface after a few hours would be minimal.  Obviously a whole city paved with concrete has proven to make a pretty big difference though.

A couple/few degrees plus a shorter duration could be a good tool for those of us that battle frost or freezing temps a handful of nights each year. 

[Looking Glass]

The front my my house is L-shaped facing due south, with the bend, blocking west winds.  Lots of poured concrete driveway, and big slabs for the sidewalk, a concrete planter, and block/concrete walls.   The sun hits it in the AM and bakes the whole area.   On cool nights the concrete stays very warm on bare feet all night, and when you walk up to the house, it feels at least 10 degrees warmer near the overhangs and door.  Very noticeable.  Definitely dramatically warmer on winter nights as the sun angles south.  

Part of my landscaping was actually set up to block all that sun, as it’s a daytime oven for the other half of the year.  

Concrete combined with the right sun angle definitely makes a difference.  Even though it’s perhaps luck of the draw, you could plan your planting on the circumstances. 

Edited October 19, 2023 by Looking Glass

[flplantguy]

With this last summer being so hot I'm considering doing the opposite.  Or maybe something that's only very apparent on those coldest nights anyway.  I'll never be able to grow 10b stuff even protected here, so courting the Japanese maples (I have two that were fine this summer(!?)) and other chill tolerant plants will go better for me. If it freezes here it's slight usually and not for long, so maybe the trees will block it and ill be able to grow some cool stuff underneath with planning. Chambeyronia do fine here, I've seen a photo of one that's local that has been in Hudson for many years (enough to trunk) so that level of hardiness and better is doable at least. If I set things well and protect when needed maybe I won't need concrete everywhere.  It's looking like a good benefit takes A LOT of it.

[kinzyjr]

4 hours ago, flplantguy said:

With this last summer being so hot I'm considering doing the opposite.  Or maybe something that's only very apparent on those coldest nights anyway.  I'll never be able to grow 10b stuff even protected here, so courting the Japanese maples (I have two that were fine this summer(!?)) and other chill tolerant plants will go better for me. If it freezes here it's slight usually and not for long, so maybe the trees will block it and ill be able to grow some cool stuff underneath with planning. Chambeyronia do fine here, I've seen a photo of one that's local that has been in Hudson for many years (enough to trunk) so that level of hardiness and better is doable at least. If I set things well and protect when needed maybe I won't need concrete everywhere.  It's looking like a good benefit takes A LOT of it.

You're taking the correct approach.  Plant for where you're at vs. attempting to modify it artificially.  This little study is more of a fun project than something I think will allow folks to change an entire climate regime.  Besides, even if we all decked our property out with edge-to-edge concrete slabs, I doubt much more would survive the next "big one".  Here, the difference between 20F and 21F isn't going to save any landscapes.

[flplantguy]

If it means I can grow some of the more amazing plants from areas of the world that are cooler too I'll take it.  The deep south has so many stunning trees I want to look into growing.  I don't think it's really that cold here in freezes, it's just much cooler at night all the time than I'm used to except the three months of the summer heat wave.  Small efforts here and there I will try, but if a coconut or adonidia can't grow without me fussing all winter it's not worth it.  I'll stick to those that can stay small in a greenhouse like the Drymophloeus I'm trying not to kill.

[kinzyjr]

In order to put faces with names, here are the objects that are being measured:

The objects in the Royal area: 1) Retaining Wall; 2) Black Scalloped Edging; 3) Typical Scalloped Edging

The back sidewalk area: 1) Black Step Pad pressed into a concrete slab; 2) Brown Clay Bricks; 3) Red Clay Bricks; 4) Sidewalk Near Bricks

Near the sidewalk: 1) Crushed concrete; 2) Alameda edgers

The south entrance area: 1) Black concrete pillar; 2) Red step pad

The Maypan Area: 1) Retaining Wall; 2) Step Pad; 3) Concrete slab with exposed portion painted black

Entryway Area: 1) Big Black Block; 2) Black Barrel Edger; 3) Brick Planter

End of the Driveway: 1) Red Step Pad; 2) Black Step Pad; 3) Black Curb Concrete

Mailbox Area: Black Concrete Base for Mailbox

Curb Area: 1) Driveway (past first joint); 2) Street

Front Circular Garden: Retaining Wall Block

 

[kinzyjr]

On 10/19/2023 at 7:20 PM, flplantguy said:

If it means I can grow some of the more amazing plants from areas of the world that are cooler too I'll take it.  The deep south has so many stunning trees I want to look into growing.  I don't think it's really that cold here in freezes, it's just much cooler at night all the time than I'm used to except the three months of the summer heat wave.  Small efforts here and there I will try, but if a coconut or adonidia can't grow without me fussing all winter it's not worth it.  I'll stick to those that can stay small in a greenhouse like the Drymophloeus I'm trying not to kill.

Coconuts are somewhat of a nail-biter everywhere.  Adonidia merrillii tend to handle this area a bit better than coconuts.  If you'd be worried about them all night, I'd definitely recommend against planting them, if only for sanity's sake.  Roystonea regia is a little more forgiving as far as routine chilly nights go.  When I started growing palms back in 2003, my intent was not to bother growing anything that would die at 20F or below other than an occasional coconut that I knew would eventually perish.  With Lethal Bronzing and a few well-timed gifts and can't-miss deals, I ended up with about a 50/20/30 split of bulletproof/semi-hardy/shouldn't be here. 

As far as if this information can help you pull off a few out-of-zone palms, the ideal scenario would be to have the hardscape receive winter sun and sit under canopy.  For this to happen, you'd need canopy that opens to the south.  It would also be ideal to have windbreaks to your north and west to drop the wind speed of advective fronts.  In this manner, the hardscape has all day to heat up and the canopy helps to stop the quick heat drain that happens when the hardscape faces open sky.  Just from the limited records we have so far, it would also be best if the hardscape was pressed into a concrete slab so it could store more heat.  Something like a walking path or patterned patio would give you the best shot of seeing a difference.

My experience is similar to what @Looking Glass notices.  I've had folks from the urban parts of Orlando come to visit and ask to go inside because the yard gets so hot.  One came on a day where it was ~94F in the middle of Orlando and my shade thermometer was recording 98F.  My propensity to hoard hardscape materials probably doesn't help since there is always more stuff just waiting in any open area I can find so I have components available for making garden beds when I get a spare moment.  Below is some of my "reserve hardscaping"

 

[flplantguy]

I bought an experimental adonidia that I'm going to observe and see how it does like a canary in the coal mine lol.  it's sitting next to the Japanese maple making for an odd juxtaposition but it's would be cool to see that mix of plants I would have confused guests lol.

[kinzyjr]

One aspect that may have a fair impact on a small semi-enclosed area is the type of mulch used in the beds.  While wood mulches do a great job breaking down and improving soil quality over time, they do not store and release heat very well.  Concrete does store light as heat, but doesn't give you as clean a look as a rounded stone would.  Another option is marble, although it is an expensive one compared to the alternate available mulches.  I've added this to my south coconut bed and have noticed that the area stays warmer overnight and the stones stay warm to the touch for a good while after sundown.

From the Big Blue Box: https://www.lowes.com/pd/Sunniland-0-5-cu-ft-Black-Marble-Chips/3122199

This effect will probably not carry over as well to gardens that are more open than my enclosed pathway on the south end, but marble does have the same specific heat capacity as concrete: https://www.designingbuildings.co.uk/wiki/Specific_heat_capacity

[RFun]

On 10/10/2023 at 1:47 PM, flplantguy said:

I watch those fronts a lot to see where the warmest spots are.  My hope is the inland development near me, and the current industrial and commercial corridor i border, will add latent heat nearby and block cold from building up.  Between that and my landscaping I'm hoping I block a lot of the coldest air on those few freeze nights without it being as intense an effect as a large city.  Just stopping frost like in pinellas county would be awesome.

With a situation such as those early season cold fronts, whichever areas are nearby buildings/in denser areas of human construction are going to be warmer for longer since they were able to absorb heat better.  This effect will be reduced as long as the high temperatures are not able to climb enough to have that much of an effect on heat absorption by the building materials, etc.

You'll get a better gauge of the warmer areas if the serious cold fronts hit this region and are able to settle in for a bit.  Observe any weather stations in the area at that time.