Stones and Stone Mulch

[Leelanau Palms]

In many of the pictures on Palmtalk, I see rings of stones around the base of palms, as well as stone/gravel mulchs used in a circle around palm trunks. Esthetics/looks are always a factor,  but I wonder if there is a functional role for these stones beyond a simple, attractive (moisture retaining, weed suppressing) mulch, such as heat retention.  Would love to hear what y'all have to say.

[RFun]

54 minutes ago, Leelanau Palms said:

In many of the pictures on Palmtalk, I see rings of stones around the base of palms, as well as stone/gravel mulchs used in a circle around palm trunks. Esthetics/looks are always a factor,  but I wonder if there is a functional role for these stones beyond a simple, attractive (moisture retaining, weed suppressing) mulch, such as heat retention.  Would love to hear what y'all have to say.

Stones are going to create a microclimate for the surrounding area.  Much like how a stream will do the same.  So you might see frost in certain areas, but you won't see any around the stones.  So, it keeps the ground warmer in that area.

[Las Palmas Norte]

Stone / rock attracts and absorbs the temperature of it's surroundings and slowly releases that when ambient temperatures change. That may be a double edged sword during the freeze thaw cycle. In a warming event, rock releases it's cold slower in a more prolonged manner. Conversely during a cooling trend, releasing heat as the surrounding temperatures decrease.

[BeyondTheGarden]

I have recently changed my mind on this.  The theory is that geological materials act as a thermal battery, slowly transferring heat energy which is sometimes but not always advantageous, as @Las Palmas Norte pointed out.  Microclimates are sometimes a double-edged sword that can reduce ultimate lows but can also significantly slow the following morning's rewarming process, and this can often be crucial as it not only the ultimate low, but also the duration of cold that matters.  This can be compounded by being on a northern aspect where sunlight doesn't strike the rocks, or it could be positively influenced if the rocks face south and receive sunlight in early morning.  Which is sometimes a problem, especially in winter, when the sun is lower in the sky and shadows are longer.  

Anyway, that aside, I have recently learned that the whole point of wood mulch is not to look nice and keep down weeds, but to add a layer of biological material that will break down and compost over 6 months-a year.  There are articles on the catastrophic effect of removing canopy trees in the Amazon basin, and how the removal of the constant supply of leaf litter destroys the soil (and not just the ecosystem big-picture).  Additionally, decaying wood mulch (specifically) seems to foster the growth of fungus, bacteria, microbes,etc that seem to also be beneficial for palms (and many other things)  I'm not smart on this but I know I have read articles and seen videos about it. 

[RFun]

No need to over complicate anything.  Better to have those stones than not to have them in order to keep things warmer.  The ground doesn't release heat at a lightning fast rate either.  Yes, those stones will be releasing that heat during those cool off periods.  That is a good thing for the surrounding area as the heat gets radiated to that area.

Edited December 28, 2023 by RFun

[Las Palmas Norte]

2 hours ago, BeyondTheGarden said:

...This can be compounded by being on a northern aspect where sunlight doesn't strike the rocks, or it could be positively influenced if the rocks face south and receive sunlight in early morning. ...

I agree. During a winter cold snap I've seen shaded large rock faces that have ice formed from what would normally be water run-off. When the weather warms, those rock faces retain freezing thermal characteristics and the ice remains for days sometimes, whereas other surrounding material thaws much more hastily. Similar rock faces in summer sun/heat radiate that heat thru the night hours.

[Harry’s Palms]

When I bought my home , I pulled up all the sod because I had a lot of palms to plant and didn’t want to navigate a mower around the palms. I replaced the lawn with black beach pebbles . They are smooth and medium to small sized . They don’t hurt my feet when walking bare foot in my yard . I didn’t put any barrier under them so about once a month I have to pull weeds to keep it looking nice. I clear the pebbles away and put stone rings where the palms are planted with mulch bark to aid with moisture retention for the feeder roots on the surface. As the palms grow, I widen the circle of stones and add bark. I’m not sure if the stones help with any heat retention , we rarely see frost where I am 

[Banana Belt]

I have piled a thick layer of stones around many of my palms, not for thermal issues but for ballast.  A thick layer of rocks placed around a palm or well placed boulders will provide ballast to help prevent wind damage.  Palms such as Queens can suffer root damage during strong winds where the tree rocks back and forth breaking and damaging the root system.  Many other palms can suffer damage to their roots during strong wind storms, a heavy layer of rocks around the base of the tree helps stabilize the palms during strong wind gusts.

I learned this lesson after a period of strong wind storms when one of two Queen Palms fell over.  The other which did not fall was growing in a large boulder Rock Garden and was stable.