Red Lava Rock Mulch

[Looking Glass]

I’m curious if anyone thinks that growing palms under lava rock mulch has positive effects in certain environments…  nutrient-wise.   

There are two Foxtail plantings within sight of my driveway.  Neither get fertilized, both get irrigation. They are about 100 feet apart.   Soil here is mostly sand.  

These get more irrigation, wood mulch occasionally….  They have severe iron, potassium, and nitrogen deficiency….

 

These get less irrigation, but get some of my lawn fertilizer, most likely….  (Though they looked good before I moved in).  They have only mild potassium deficiency.  There is overlying red lava mulch in their bed.   These seems to be the only differences.  

I was at Lowes today, and bought a bag of crushed red lava rock, and put it around the Alfredii and the Carlsmithii (these suffer from iron issues for me).   I wonder if it will make a difference?  Probably not, but what the hell…

I wonder if some of the iron and other minerals leach out of the lava over time.  I’m still a big fan of organic, rotting wood mulch in our sand.  

Edited December 14, 2022 by Looking Glass

[Silas_Sancona]

8 minutes ago, Looking Glass said:

I’m curious if anyone thinks that growing palms under lava rock mulch has positive effects in certain environments…  nutrient-wise.   

There are two Foxtail plantings within sight of my driveway.  Neither get fertilized, both get irrigation. They are about 100 feet apart.   Soil here is mostly sand.  

These get more irrigation, wood mulch occasionally….  They have severe iron, potassium, and nitrogen deficiency….

 

These get less irrigation, but get some of my lawn fertilizer, most likely….  (Though they looked good before I moved in).  They have only mild potassium deficiency.  There is overlying red lava mulch in their bed.   These seems to be the only differences.  

I was at Lowes today, and bought a bag of crushed red lava rock, and put it around the Alfredii and the Carlsmithii (these suffer from iron issues for me).   I wonder if it will make a difference?  Probably not, but what the hell…

I wonder if some of the iron and other minerals leach out of the lava over time.  I’m still a big fan of organic, rotting wood mulch in our sand.  

Yes, w/ any stone, as it is weathered,  various nutrients / elements -that the rock is made of- will leach into the soil as the rock is broken down into smaller and smaller particles. Process is slower than nutrient release from organic sources of course, but is more steady over a longer period of time. 

  Difference between red and black colored Lava rock comes down to the age of the rock itself... Fresh lava is typically black,  while older stone slowly ages to brownish or red due to oxidation of the iron content in it over time < While all 3 basic types of Lava have both elements in them, Mafic Lava often contains the highest %'ages of both Iron and Magnesium > .   Is also considered Acidic, so laying it down can effect soil PH  -to some degree at least..  Porous nature of the stone also helps drain excess moisture, but retains / slowly releases some..

  Depending on the type, or factors involving how it was formed,  some lava can contain higher levels of K.  Many Granite type rocks, also Igneous in origin, do for sure  due in part to how they formed..  Pink, Red, or Orange-ish " stained " Granite is another example of the high iron content present in that particular type of Granite rusting over time when exposed to air / weathered by water.  Same could be said of red colored Sand Stone as well..

Here's an article on Lava rock: https://sciencing.com/composition-lava-rock-8067279.html

 

[Kim]

I don't know much about mineral content, but we never use red lava for planting mix in Hawaii. Black lava, yes, all the time. Red lava seems to inhibit growth; some plants struggle if planted in it. I have some Licuala that should be taller after 12 years in the ground, but they were planted in a soil pile that included red lava, and at the time, I didn't know the difference. I mostly use the red lava for paths. Using it as a top dressing, maybe not much impact on the palms? I don't use it for that, either, never really cared for the look. Reminds me more of the desert than of a tropical locale.

[mnorell]

I was trying to figure out recently why Chrysalidocarpus decaryi in the desert seem to be lackluster, often the older leaves have been trimmed by the owners/maintenance crews, whereas in the cooler coastal areas they can really look fantastic (think about those beautiful peacock-like specimens in Balboa Park in San Diego)...this not making too much sense when you look at the climate from which they hail. They should flourish in a hot climate, and they grow in association with Aluaudia, Uncarina,  and other plants that grow like natives out here in the Palm Springs area. When I looked further into it, though, I noticed that they grow on laterite soils, which are characterized by their red color, high iron oxide content along with a Bauxite-like Aluminum ore. Though their middling performance may be due to other factors such as extreme sun exposure in summer, I think I will try to plant my Triangle seedlings into red lava-amended soil and see if I can get better results, hopefully holding more leaves as adult palms.

[Fishinsteeg234]

@Looking GlassGood question, I’m curious to what fellow PT’ers have to say about the lava rock/gravel experience. The first pic of the yellow stressed foxtails makes me think they could have exposed to chemicals from keeping the paver driveway clean. The driveway appears to slope towards the garden bed, and those pavers appear well maintained and regularly bleached clean. Maybe environmental factors such as chemical runoff is possibly causing the long term yellowing and stunting? 
 

I’m a believer in heavy wood mulch as opposed to gravel mulch beds here in hot and humid florida. I have always believed the quick breakdown of wood mulch into black gold nutrient-rich soil is the key to successful paintings. I was also under the impression rocks and other gravel/stone material take millennia to break down into finer, usable minerals. Lava rock is probably quicker to break down than other rocks, but probably still much longer a palm’s life cycle if I were to guess. 

[Looking Glass]

3 hours ago, Kim said:

I don't know much about mineral content, but we never use red lava for planting mix in Hawaii. Black lava, yes, all the time. Red lava seems to inhibit growth; some plants struggle if planted in it. I have some Licuala that should be taller after 12 years in the ground, but they were planted in a soil pile that included red lava, and at the time, I didn't know the difference. I mostly use the red lava for paths. Using it as a top dressing, maybe not much impact on the palms? I don't use it for that, either, never really cared for the look. Reminds me more of the desert than of a tropical locale.

I would assume that red lava rock is higher in iron oxide due to the color.  This might be good, bad or neutral depending on the environment.   The sand-soil here has a lot of issues with iron, potassium, and sometimes magnesium.  I hate the look of it also.   Don’t much care for red wood mulch either. 

Here, black is hard to come by.  Red is in every store, along with 20 other kinds of rock.  
 

Edited December 15, 2022 by Looking Glass

[Looking Glass]

32 minutes ago, Fishinsteeg234 said:

@Looking GlassGood question, I’m curious to what fellow PT’ers have to say about the lava rock/gravel experience. The first pic of the yellow stressed foxtails makes me think they could have exposed to chemicals from keeping the paver driveway clean. The driveway appears to slope towards the garden bed, and those pavers appear well maintained and regularly bleached clean. Maybe environmental factors such as chemical runoff is possibly causing the long term yellowing and stunting? 
 

I’m a believer in heavy wood mulch as opposed to gravel mulch beds here in hot and humid florida. I have always believed the quick breakdown of wood mulch into black gold nutrient-rich soil is the key to successful paintings. I was also under the impression rocks and other gravel/stone material take millennia to break down into finer, usable minerals. Lava rock is probably quicker to break down than other rocks, but probably still much longer a palm’s life cycle if I were to guess. 
 

That driveway is never washed.   At least not in 3 years so far.  Won’t even use roundup in the cracks, just vinegar.   There are 4 other palms species there doing well.  Ornamental grasses and bromeliads doing well there.  

I too think wood mulch is essential here.  I shovel it as fast as it breaks down.  I add dolomite and shells on some palms (Pseudophoenix and Cuban stuff).  I just wonder if adding some lava rock would leach some beneficial iron, potassium, magnesium to others.  Maybe…. Maybe not….  Not thinking to make a full bed of it.   Just a smattering.  

 

[mnorell]

The thing I think with Wodyetia is just that it is an intolerant palm when it comes to minor elements. Some growers from Darwin and Cairns have commented on this in the past and it would be worth searching old posts for the info on their natural environment. I can certainly say that in my years of living in the Keys I think I rarely saw one that looked any good. They just always are chlorotic and nasty-looking. I think they are just a real problem in Florida due to the calcareous nature of the soils in most areas there. Perhaps getting some Nutrikote time-release fertilizer. Make sure you get one of their mixes composed of sucrates and not oxides or sulfates, which have no or limited ability to get to your plant in highly basic substrates...the sucrate forms stay available even in those high pH environments for a good amount of time and present your best hope of getting them to look good. My ultimate suggestion would be to get some Syagrus sancona, the "Colombian Foxtail," and let that be your substitute. They are easy and beautiful palms!

[Looking Glass]

3 hours ago, Silas_Sancona said:

Yes, w/ any stone, as it is weathered,  various nutrients / elements -that the rock is made of- will leach into the soil as the rock is broken down into smaller and smaller particles. Process is slower than nutrient release from organic sources of course, but is more steady over a longer period of time. 

  Difference between red and black colored Lava rock comes down to the age of the rock itself... Fresh lava is typically black,  while older stone slowly ages to brownish or red due to oxidation of the iron content in it over time < While all 3 basic types of Lava have both elements in them, Mafic Lava often contains the highest %'ages of both Iron and Magnesium > .   Is also considered Acidic, so laying it down can effect soil PH  -to some degree at least..  Porous nature of the stone also helps drain excess moisture, but retains / slowly releases some..

  Depending on the type, or factors involving how it was formed,  some lava can contain higher levels of K.  Many Granite type rocks, also Igneous in origin, do for sure  due in part to how they formed..  Pink, Red, or Orange-ish " stained " Granite is another example of the high iron content present in that particular type of Granite rusting over time when exposed to air / weathered by water.  Same could be said of red colored Sand Stone as well..

Here's an article on Lava rock: https://sciencing.com/composition-lava-rock-8067279.html

 

It’s hard to figure out just surfing around, but it appears that there are mineral differences based on the color also, which would make sense.  I wonder how readily they leach out….  Is it like limestone?  Or more like granite?  

[Looking Glass]

8 minutes ago, mnorell said:

The thing I think with Wodyetia is just that it is an intolerant palm when it comes to minor elements. Some growers from Darwin and Cairns have commented on this in the past and it would be worth searching old posts for the info on their natural environment. I can certainly say that in my years of living in the Keys I think I rarely saw one that looked any good. They just always are chlorotic and nasty-looking. I think they are just a real problem in Florida due to the calcareous nature of the soils in most areas there. Perhaps getting some Nutrikote time-release fertilizer. Make sure you get one of their mixes composed of sucrates and not oxides or sulfates, which have no or limited ability to get to your plant in highly basic substrates...the sucrate forms stay available even in those high pH environments for a good amount of time and present your best hope of getting them to look good. My ultimate suggestion would be to get some Syagrus sancona, the "Colombian Foxtail," and let that be your substitute. They are easy and beautiful palms!

I don’t have much interest in Foxtails myself.   Just in my neighbor’s as “canaries in the coal mine”.  I wonder why two groups separated by 100 feet and both non-fertilized vary from terrible to pretty good looking.   I do think about sneaking next door with a bag of palm fertilizer and langbeinite some night though.   I’m more interested in helping my Carlsmithii.   It only responds a little to EDDHA iron, through it is still putting out about 2.5 11 foot pale leaves per year.  

[Silas_Sancona]

13 minutes ago, Looking Glass said:

I would assume that red lava rock is higher in iron oxide due to the color.  This might be good, bad or neutral depending on the environment.   The sand-soil here has a lot of issues with iron, potassium, and sometimes magnesium.  I hate the look of it also.   Don’t much care for red wood mulch either. 
 

Since it contains the same high Iron / Magnesium properties, you could use black lava as well. There is also a stone offered there ( or, maybe it isn't available any more?? ) called "Timberlite" that is essentially earth tones ..Tan, sandy light brown, brown ..with hints of Red, and Black in it. Is supposedly a type of Volcanic rock, but have also heard it was man made. Regardless, is essentially " Lava" rock, and is very porous ( and light ). I have some, but wish i had brought several bags w/ me when i moved..

Red lava, like how you're using it, is ok.. but yes, lol.. A yard full of it is pretty harsh on the eyes ( red colored mulch as well, lol ). Don't know of any part of the desert around here that is that red, lol..

44 minutes ago, Fishinsteeg234 said:

@Looking GlassGood question, I’m curious to what fellow PT’ers have to say about the lava rock/gravel experience. The first pic of the yellow stressed foxtails makes me think they could have exposed to chemicals from keeping the paver driveway clean. The driveway appears to slope towards the garden bed, and those pavers appear well maintained and regularly bleached clean. Maybe environmental factors such as chemical runoff is possibly causing the long term yellowing and stunting? 
 

I’m a believer in heavy wood mulch as opposed to gravel mulch beds here in hot and humid florida. I have always believed the quick breakdown of wood mulch into black gold nutrient-rich soil is the key to successful paintings. I was also under the impression rocks and other gravel/stone material take millennia to break down into finer, usable minerals. Lava rock is probably quicker to break down than other rocks, but probably still much longer a palm’s life cycle if I were to guess. 

How quickly certain types of stone "decompose" / Weather down,  ..whatever you want to call the break down process occurs depends on the composition of the stone itself, and other factors like how much heat / cold exposure, wind, water and chemical weathering it experiences.. Obviously, softer stone like Mud, clay-ey Limestone or Gypsum, softer Lava, Pumice,  and Sandstone can weather faster than really dense Schist or Marble ...or certain fine-graned Granites and Rhyolite. 

That said, i can visit the same areas out the desert and see where massive boulders ( Mainly Granite and Rhyolite in those areas ) have shed pieces, sometimes massive slabs, or shattered into large sections fairly recently..  There are also certain types of large-grained Granites here that will break apart in your hand, almost like Styrofoam, or with fairly light pressure. Much less than you'd assume it would take to break a basketball- sized chunk into hundreds of pieces.  On a larger scale, it is easy to see that, at least w/ those rock types, decomposition is pretty quick.

 

[Silas_Sancona]

23 minutes ago, Looking Glass said:

It’s hard to figure out just surfing around, but it appears that there are mineral differences based on the color also, which would make sense.  I wonder how readily they leach out….  Is it like limestone?  Or more like granite?  

Figure that every time it rains, a pulse of nutrients is being washed off the rock, into the soil, no matter what the composition of the stone is..  I'm sure there is a way to measure it, but think the set up would getting " base" readings from the stone,  and the soil ..then taking readings of collected water that had washed off the stone after a good downpour, and also testing the soil to see what differences the stone might be making compared to an area w/ out rock laid down..

I'm sure you know this but the other important thing to factor too is, if the soil is low ..or devoid of Mycorrhize  that work to make X element available for uptake by X plant's roots,  then adding something like Lava / other specific rock, which might act as a slow, but steady long term source of Iron ..or whatever other element that might be needed.. isn't going to produce the same, or as good results as if there is a healthy population of those organisms already thriving in the soil. Obviously, that is where a steady supply of organics comes in.. 

Whether that means throwing down mulch once or twice yearly, or allowing all ..or a comfortable level of..  leaves, spent flowers / fruit shed by everything growing in that area ..or the yard, to decompose on top of, then down into the soil..  all of it works as an organic material source to feed the microbes below.. Keep them happy, they'll keep everything else happy.

[Silas_Sancona]

One last thing i'll add that many people may not be aware of,  Lichen which colonize rocks, help break down rocks,  and contribute both to nutrient cycling, and soil building.  "Moss" that grows on rock performs a similar job.

Here's one article w/ a quick discussion of how the process occurs. https://coloradolichens.org/2013/12/26/lichens-and-rocks/

[Mr. Coconut Palm]

I have heard on a Texas all organic weekend gardening program called South Texas Gardening with Bob Webster on San Antonio AM 550, that lava rock is very good for plants.  He has a guest on his program on Saturday mornings at 8:00 am Central Time, named Howard Garrett (the Dirt Doctor) who has lots of good information and a very informative program himself, as well as an extremely informative website at the DirtDoctor.com

With that said, I have used red lava rock around the base of my two in ground Coconut Palms here in Flour Bluff on the east side of Corpus Christi, Texas, near the Laguna Madre (Climate Zone 10A).  I did this mostly to improve wintertime soil temps, since Coconut Palms are marginal here, and we get some chilly winters at times, but I also did it based on the info I heard on the above mentioned program of how lava rock benefits plants.  Hawaii, being all volcanic islands seems to have the most beautiful, luxuriants tropical trees and plants in the whole world, so there must be something to it.  My Coconut Palm closest to my house, planted just off the front patio is a Green Malayan Dwarf that is about 11 ft. tall in overall height, and has been in the ground since May of 2021, and is growing very robustly, with large new leaves emerging now.  The other one I have, is planted further out into the yard, with no real protection from the house, and is also about 11 ft. tall in overall height.  It is a Panama Tall, but has less robust leaves, but a slightly wider base of the trunk.  They were both pretty badly injured from 4 freezes and about 20 nights in the 30'sF last winter, with only protection in the form of blankets, sheets, and towels wrapped around the trunks and base of the crown on the coldest night (28F) and the last cold night of the season (about 41F) in March, but no other protection the rest of the winter.  The Green Malayan Dwarf was quicker to recover and with more robust growth, but still took a while to start recovering than the Panama Tall, and the Green Malayan is about 4 or 5 months older.  I also have a cluster of 4, 6 ft. tall Christmas Palms planted at the south corner of the front flower bed (that was a cluster of 4 prior to last winter), that was planted at about the same time last year as the two Coconut Palms.  They also has had red lava rock around the base of it too all this time, and was only protected in the same way on the same two cold nights last winter.  They took a while to recover too, but were looking great about 3 weeks ago, prior to showing signs of cold weather (non freezing) stress from two straight weeks of highs in the 50'sF and low to mid 60'sF, and lows in the 40'sF to around low 50'sF (when highs and lows  should have been in the upper 70'sF and upper 50'sF to around low 60'sF) back in November.  I hope this info helps in answering some of the questions about the use of red lava rock.  At least these are my observations from growing two tropical species in a marginal climate for them.

John

[Looking Glass]

1 hour ago, Silas_Sancona said:

Figure that every time it rains, a pulse of nutrients is being washed off the rock, into the soil, no matter what the composition of the stone is..  I'm sure there is a way to measure it, but think the set up would getting " base" readings from the stone,  and the soil ..then taking readings of collected water that had washed off the stone after a good downpour, and also testing the soil to see what differences the stone might be making compared to an area w/ out rock laid down..

I'm sure you know this but the other important thing to factor too is, if the soil is low ..or devoid of Mycorrhize  that work to make X element available for uptake by X plant's roots,  then adding something like Lava / other specific rock, which might act as a slow, but steady long term source of Iron ..or whatever other element that might be needed.. isn't going to produce the same, or as good results as if there is a healthy population of those organisms already thriving in the soil. Obviously, that is where a steady supply of organics comes in.. 

Whether that means throwing down mulch once or twice yearly, or allowing all ..or a comfortable level of..  leaves, spent flowers / fruit shed by everything growing in that area ..or the yard, to decompose on top of, then down into the soil..  all of it works as an organic material source to feed the microbes below.. Keep them happy, they'll keep everything else happy.

I agree.  I’m a firm believer in soil composition and health.   It’s everything.  My grandmother taught me that as a small child in her beautiful massive garden.  A fraction of her green thumb, and love of nature, lives on in me, to some degree.  

I lay down mulch and compost and other detritus as much as possible.  If you dig in the beds near the house, it’s all white fungi strands and worms.  When I moved in, I put down a foot of manure, peat, and topped it with wood mulch.  Now I mulch 2-3x per year.  It decomposes fast in the heat and humidity.   

But trained in the sciences, I’m also not above a little help beyond this, and deep dives into “why and how?”.  I use quality fertilizers, lots of potassium too.  Iron sometimes.   Other additives too…

What you describe with the lava stone would be quite a project, and even if you could measure differences, they might not translate to measurable growth results, though if there were no differences, there would be no results either.  It would make a good grad school project.  You could devise a series of interesting quantitative and qualitative experiments for sure.  And results would vary based on your native ground composition.  

For now, I’ll have to settle on the weakest and lowest level of evidence…. Anecdotal results.  It often starts there though.  

I realize that I know little about stones in general.  
 

54 minutes ago, Mr. Coconut Palm said:

I have heard on a Texas all organic weekend gardening program called South Texas Gardening with Bob Webster on San Antonio AM 550, that lava rock is very good for plants.  He has a guest on his program on Saturday mornings at 8:00 am Central Time, named Howard Garrett (the Dirt Doctor) who has lots of good information and a very informative program himself, as well as an extremely informative website at the DirtDoctor.com

With that said, I have used red lava rock around the base of my two in ground Coconut Palms here in Flour Bluff on the east side of Corpus Christi, Texas, near the Laguna Madre (Climate Zone 10A).  I did this mostly to improve wintertime soil temps, since Coconut Palms are marginal here, and we get some chilly winters at times, but I also did it based on the info I heard on the above mentioned program of how lava rock benefits plants.  Hawaii, being all volcanic islands seems to have the most beautiful, luxuriants tropical trees and plants in the whole world, so there must be something to it.  My Coconut Palm closest to my house, planted just off the front patio is a Green Malayan Dwarf that is about 11 ft. tall in overall height, and has been in the ground since May of 2021, and is growing very robustly, with large new leaves emerging now.  The other one I have, is planted further out into the yard, with no real protection from the house, and is also about 11 ft. tall in overall height.  It is a Panama Tall, but has less robust leaves, but a slightly wider base of the trunk.  They were both pretty badly injured from 4 freezes and about 20 nights in the 30'sF last winter, with only protection in the form of blankets, sheets, and towels wrapped around the trunks and base of the crown on the coldest night (28F) and the last cold night of the season (about 41F) in March, but no other protection the rest of the winter.  The Green Malayan Dwarf was quicker to recover and with more robust growth, but still took a while to start recovering than the Panama Tall, and the Green Malayan is about 4 or 5 months older.  I also have a cluster of 4, 6 ft. tall Christmas Palms planted at the south corner of the front flower bed (that was a cluster of 4 prior to last winter), that was planted at about the same time last year as the two Coconut Palms.  They also has had red lava rock around the base of it too all this time, and was only protected in the same way on the same two cold nights last winter.  They took a while to recover too, but were looking great about 3 weeks ago, prior to showing signs of cold weather (non freezing) stress from two straight weeks of highs in the 50'sF and low to mid 60'sF, and lows in the 40'sF to around low 50'sF (when highs and lows  should have been in the upper 70'sF and upper 50'sF to around low 60'sF) back in November.  I hope this info helps in answering some of the questions about the use of red lava rock.  At least these are my observations from growing two tropical species in a marginal climate for them.

John

Definitely, Mr Coconut.  Any information helps.  Glad to hear of your successes.  I try to temper my emotions and see things clearly whenever possible, within the limits of my own foolishness.  I agree with a great deal of what you say, and have said in the past.  I try to keep a balance between hard science and the real-world experiences of others.  One foot in each world.  And that’s the beauty and power of this forum, and others like it.  I’ll soak up knowledge and information without prejudice.  Keep it coming.  I have not listened to your “Dirt Doctor” but I would like to hear what he has to say.   

Any thoughts from @sonoranfans…. What say you!?!  

Edited December 15, 2022 by Looking Glass

[sonoranfans]

Fe deficiency is usually a pH problem and adding Fe doesnt help since it is not bioavailable at alkaline pH.  Sand under and rock on top sound like a cation exchange issues as well, not much there.  Since you have sandy soil I suspect that overwatering is not an issue but that also causes Fe deficiency.  I would try chelated Fe and see how that works, but you might be trying to swim up a waterfall with foxtails in alkaline soils.  I would get some pH testing done, on soil at the two sites.  I don't see any kind of rock topping making up for really sandy soils, cation exchange wise.  In clayish soils red laval rock could work better since clay would in principle -with its high cation exchange- absorb and retain nutrients coming off the laval rock.  Sand doesn't retain anything.  Rain will wash it out fast.  The rock will dissolve slowly, perhaps too slow for feeding in sandy soils.  

[realarch]

Here in East Hawaii, some of us refer to foxtails as 'fertilizer hogs.' The Hawaii Island Palm Society maintains the palm collection at the local zoo and the Wodyetia require more regular fertilizing than any of the other plantings. There must be 24 of them, planted in turf, lining the entrance road to the facility creating a rather formal entry. The look is striking when they are at their best. You could probably mulch the heck out of them, but that would alter the look the admin is seeking. Because of the copious amount of rainfall, you see them yellowed out all over town regardless of the amount of black lava rock used as a soil medium. They do respond rather quickly to a good micro nutrient fertilizer and for a time look robust and green. Incidentally, they were planted many years ago when foxtails were rare and seed expensive and hard to obtain. 

Normanbya on the other hand, always look great with little care and maintenance.

Tim  

[Looking Glass]

4 hours ago, sonoranfans said:

Fe deficiency is usually a pH problem and adding Fe doesnt help since it is not bioavailable at alkaline pH.  Sand under and rock on top sound like a cation exchange issues as well, not much there.  Since you have sandy soil I suspect that overwatering is not an issue but that also causes Fe deficiency.  I would try chelated Fe and see how that works, but you might be trying to swim up a waterfall with foxtails in alkaline soils.  I would get some pH testing done, on soil at the two sites.  I don't see any kind of rock topping making up for really sandy soils, cation exchange wise.  In clayish soils red laval rock could work better since clay would in principle -with its high cation exchange- absorb and retain nutrients coming off the laval rock.  Sand doesn't retain anything.  Rain will wash it out fast.  The rock will dissolve slowly, perhaps too slow for feeding in sandy soils.  

Yeah.  It’s seems that 99% of it would be unavailable at my pH.  Alfredii responds well to EDDHA chelated iron, but Carlsmithii shows only slight improvement.  Otherwise overall fertilizer levels are pretty high for the rest of the elements.  

I cut the water way back on these two this year.  

B. Alfredii doing OK…..

 

C. Carlsmithii always a little limey-yellow….  Hard to get a decent pic, but puts out huge fronds from the ground.  

I think Foxtails do ok around here, if people dump tons of fertilizer and water on them, which regular folk don’t normally do.   They are pretty common here, and many pretty commonly look bad too.