Rocky soil

[Than]

I hope I am posting in the right subforum. So, to my dismay, I recently discovered that under the top layer of my newly acquired land, there are rocks. We are talking big and small rocks, everywhere. It was hard even for the hard machinery to dig. They suggested I add soil on top. The other solution would be to bring special machinery to try and break and remove as much stone as possible but that would be costly probably..

What depth should soil have for palms and other trees and shrubs? Would 15 inches (40 cm) suffice? 

Anyone else with rocky soil here? 

[Phoenikakias]

5 minutes ago, Than said:

I hope I am posting in the right subforum. So, to my dismay, I recently discovered that under the top layer of my newly acquired land, there are rocks. We are talking big and small rocks, everywhere. It was hard even for the hard machinery to dig. They suggested I add soil on top. The other solution would be to bring special machinery to try and break and remove as much stone as possible but that would be costly probably..

What depth should soil have for palms and other trees and shrubs? Would 15 inches (40 cm) suffice? 

Anyone else with rocky soil here? 

 

You are f*. Imo 3 ft top soil will be necessary. A very famous palm collector in SCa with probably the best collection of Malagasian palms beyond the tropics, Mardy Darian, had created a top soil of 9 ft. If your property is flat, you can at least create some planters with top soil.

[Than]

2 minutes ago, Phoenikakias said:

 

You are f*. Imo 3 ft top soil will be necessary. A very famous palm collector in SCa with probably the best collection of Malagasian palms beyond the tropics, Mardy Darian, had created a top soil of 9 ft. If your property is flat, you can at least create some planters with top soil.

9 feet????? That's 3 metres! My property will rise above the surrounding roads, will have to build concrete fence.. oh dear... 😭

[Phoenikakias]

I did not suggest that you follow this example, I mentioned it only to show how far one may go lol. Hopefully Californians will post here their own personal experience and the usual depth of top soil.

[Navarro]

Es tierra de relleno la que tienes en tu propiedad ?  o es la de origen?

[Brad52]

I have at most 2-3” (yes, inches) of ‘soil’ before hitting solid lava so I’m envious of your situation!  You can make it work with berms/mounds and effort, I have planted hundreds of plants of all types and many are thriving despite the lack of soil.  Granted I’m in Hawai’i where growing is year round but when we go weeks with no rain, moisture becomes the biggest challenge and yet most of my palms do just fine w/o any rain and no ground moisture to tap into.

 

[Darold Petty]

Chamaerops can grow in areas of very poor and sparse soils. 

[Silas_Sancona]

Me myself?  i'd rather have my soil rockier than not..  Many of the coolest plants on the planet like their " dirt " chunky and well drained.   Look at Gary's ( Levine ) place..  Palms ..and other stuff planted certainly aren't " struggling " to survive there.

Plenty of photos of palms growing out of straight rock shared by various PT members  who have had the privilege of exploring various areas of the Caribbean / Mexico, Hawaii,  etc.. over the years.

More rocks,  please.. 

[Las Palmas Norte]

😄

[Phoenikakias]

50 minutes ago, Las Palmas Norte said:

😄

I can see already potassium deficiency!

[Las Palmas Norte]

4 hours ago, Phoenikakias said:

I can see already potassium deficiency!

That photo was taken in 2009 and is 20' tall now. 

[happypalms]

Rocky soil is one of the best for cool climates with thermal mass realised during the cool night I have rocks the size of cars right down to 10mm in fact I have rocks lots of them sandstone a very pourus rock it works to my advantage and sometimes to my disadvantage use them to your advantage for landscaping or thermal protection placed around the top of your plant my sandy rocky soil heats up faster in winter giving my garden an extra winter warmth one disadvantage is water drains away very quickly invest in a digging bar a long hardened piece of steel with a chisel point (best if you lend to a friend and he never gives it back) they are hard work to use one but will dig a hole to China very easily in rocky soil given strong arms doing the work look at a rainforest mostly a thin layer of topsoil and mulch with rocks underneath but given enough moisture they provide some of the best habitat for palms find pockets of soil and raise the sides with the rocks it increases the soil depth with amendments even better rocks will become your friend my days of lifting and moving them are over two double hernias later I realised to work smarter not harder go with the flow of your land and create your paradise just keep planting trees or palms install irrigation as well growing moisture loving plants irrigation is the way of the future and much better growth good luck 

[Brad52]

I’m curious how long this can last…

[SoFlo]

Don't despair! Florida Keys are rock islands with shallow to no soil and plenty of palms and plants. I've experienced T. radiata growing on the limestone and large mahogany trees in very shallow soil. Sorry Brad, I don't have any pictures. I also agree with Ph that some go to arduous lengths to accommodate certain species. I know a collector who didn't need deeper soil but used cement block to raise a couple sections of the backyard a few feet. It looked cool.

[Than]

Thanks guys, you gave me some hope.

The problem (should've mentioned in the beginning) is though that the stone will most probably be limestone which means very alkaline soil, that many (most) tropicals hate.. Not all stones are made equal. I was planning to use Syagrus as my main palm feature but it loves acidic soil.

Apparently, it is not mere stone under the ground but also building materials, bricks, concrete etc from an old building that used to exist there. Concrete is also very alkaline..

Edited February 3 by Than

[Phoenikakias]

32 minutes ago, Than said:

Thanks guys, you gave me some hope.

The problem (should've mentioned in the beginning) is though that the stone will most probably be limestone which means very alkaline soil, that many (most) tropicals hate.. Not all stones are made equal. I was planning to use Syagrus as my main palm feature but it loves acidic soil.

Apparently, it is not mere stone under the ground but also building materials, bricks, concrete etc from an old building that used to exist there. Concrete is also very alkaline..

Concrete is good, if you want blue leaves in some spp! One Californian used to plant concrete chunks in the root zone of Brahea plants in order to enhance blueness of the foliage!! (Seriously) You can also plant Thrinax, Coccothrinax and Pseudophoenix as perennials. (not seriously). 

[Phoenikakias]

Check first please the soil and irrigation water pH and in the first case of samples taken from various depths. You can buy in Temu an electronic pH tester like I did. It works with desionized water. Here are the test results reg the tap water I use also for irrigation.

 

[Tyrone]

It’s not all bad having rocks. Definitely great drainage would be guaranteed. I’d invest in a Jack hammer, or hire one and find out what is going on underground, and then try going with what you’ve got. Build up some areas. Use some rocks you’ve dug up to retain that build up soil. Leave other rocks exposed for integration with water features or be features in themselves. It’s challenging but it could be an incredible garden in the end. 
 

I visited Hyophorbe indica in the wild in Reunion island last year. There’s about 50 left in the south near Port Phillipe.  They grow on an 800 year old lava flow. Great drainage but not much soil. It’s the only place where you’ll see remnant primary forest in all the Mascarenes and there are huge trees on it. 

[James B]

Spending on you climate rocky soil is a benefit. Places with long cool winters that have clay soil can be a recipe for palms getting pink rot or other ailments that good draining soil helps protect against. In my current garden my soil full of granite rocks. My last yard had it too but not as extreme. Really the hardest part is digging holes. No issues with my palms so far.

[Than]

Some very interesting insights, thanks a lot!

Today an earthmoving technician visited my plot and told me that most stones are concrete and debris from the old building and not so much natural stones. This is good news as they can be easily removed. He told me these without digging at all (stones are not visible, they are all underground). When I asked if he would like to dig first to check he said he doesn't have to as he can tell from just looking at the soil! 🥴 He then quoted a price for removing them, which wasn't too bad.

@Phoenikakias Blue leaves?? Brahea?? NEVER! Not my cup of tea. Blue leaves should be illegal.

I do have a pH tester already and I check my water. I add a bit of vinegar every time I water (my plants are all in pots for now so it is easy). I will also do a professional soil test once earthmoving is done. My neighbour has 15 cats which sh!t the cr@p out of themselves in my plot so I expect lots of free organic matter!

@Tyrone true, I will have to build raised beds and do some extra work but some stones may be used to my benefit. Of course I cannot compare lava to our ^#&%^*(&^% limestone..

Edited February 3 by Than

[Than]

1 minute ago, James B said:

Spending on you climate rocky soil is a benefit. Places with long cool winters that have clay soil can be a recipe for palms getting pink rot or other ailments that good draining soil helps protect against. In my current garden my soil full of granite rocks. My last yard had it too but not as extreme. Really the hardest part is digging holes. No issues with my palms so far.

Oh I wish it were granite.. It'll probably be limestone and debris. If I do find granite though, I'll def leave it there.

[Phoenikakias]

15 minutes ago, Than said:

Some very interesting insights, thanks a lot!

Today an earthmoving technician visited my plot and told me that most stones are concrete and debris from the old building and not so much natural stones. This is good news as they can be easily removed. He told me these without digging at all (stones are not visible, they are all underground). When I asked if he would like to dig first to check he said he doesn't have to as he can tell from just looking at the soil! 🥴 He then quoted a price for removing them, which wasn't too bad.

@Phoenikakias Blue leaves?? Brahea?? NEVER! Not my cup of tea. Blue leaves should be illegal.

I do have a pH tester already and I check my water. I add a bit of vinegar every time I water (my plants are all in pots for now so it is easy). I will also do a professional soil test once earthmoving is done. My neighbour has 15 cats which sh!t the cr@p out of themselves in my plot so I expect lots of free organic matter!

@Tyrone true, I will have to build raised beds and do some extra work but some stones may be used to my benefit. Of course I cannot compare lava to our ^#&%^*(&^% limestone..

 It is really a matter of pay now or pay double and triple and multiple amounts later. I use frequently lava chunks in potting mix without hesitation but lime turns organic matter quickly to mud, the perfect recipy of disaster.

[Rivera]

Inspiration to be found in the limestone cloud forests of Mexico and Guatemala. Chamaedorea species abound.

Limestone deserts and rainforests of Brazil.

Spectacular agave of Mexico's limestone cliffs in La Huasteca Canyon.

[Dr. George]

I saw this post shortly after it started on Thursday. I wanted to take a few current pics before replying and it has taken me a bit to get around to doing it, so my apologies for the delay.

First, a couple of comments, then some pics

1. Rocky soil can be your friend. Here on the Big Island of Hawaii very few of us have much soil but lots and lots of rocks. We have very rocky ground and very little natural topsoil. The important thing is making sure that you have good drainage in the holes that you prepare for planting. Dig the hole at least 12 inches wider than the pot. Fill around the root ball with good, amended soil and then mulch around the planting. If you put 4 inches of mulch around the planting yearly for 3 - 4 years you will develop a good organic base (more and much better than your neighbor's cats will do).

2. I will not pretend to know how to best deal with limestone soil as I have no experience with it.  Other folks from Florida would be more experienced and better able to discuss dealing with gardening in limestone.  As for soil ph, acidifying soil with the use of sulfur is a common practice. Takes some time, but likely will be more effective than the broad application of vinegar. Am attaching a monograph about the use of sulfur for lowering soil ph.

Lowering_Soil_pH_with_Sulfur.pdf

So, now some pics.

When we started our farm development in 2007 we brought in a Cat D9 to clear the brush, move the 4 to 6 inches of top soil and break up the underlying layers of lava down to about 3 ft depth. Then smoothed out the surface and replaced the soil. We did this on the whole parcel except for 1 acre that had ancient Hawaiian rock walls and terraces that we wanted to preserve.

 

In the 1 acre that we preserved, there was at best 1 inch of organic debris then pretty much solid lava. In the first 2 pics you can see the guys using a jack hammer in 2010 to make holes for the palm plantings. Following is a picture of the same area today.

 

This is a Royal palm in 2010, planted as a 1 gal size in 2008. You can see how rocky the ground is and our plentiful use of mulch.

This is the same spot today.

 

2010 - Very rocky environment

Same spot today.

 

2010- Very rocky environment

Same spot today.

 

2010- Very rocky environment

Same spot today.

 

Hope something here is encouraging and helpful - gmp

 

 

[Than]

1 hour ago, Dr. George said:

I saw this post shortly after it started on Thursday. I wanted to take a few current pics before replying and it has taken me a bit to get around to doing it, so my apologies for the delay.

First, a couple of comments, then some pics

1. Rocky soil can be your friend. Here on the Big Island of Hawaii very few of us have much soil but lots and lots of rocks. We have very rocky ground and very little natural topsoil. The important thing is making sure that you have good drainage in the holes that you prepare for planting. Dig the hole at least 12 inches wider than the pot. Fill around the root ball with good, amended soil and then mulch around the planting. If you put 4 inches of mulch around the planting yearly for 3 - 4 years you will develop a good organic base (more and much better than your neighbor's cats will do).

2. I will not pretend to know how to best deal with limestone soil as I have no experience with it.  Other folks from Florida would be more experienced and better able to discuss dealing with gardening in limestone.  As for soil ph, acidifying soil with the use of sulfur is a common practice. Takes some time, but likely will be more effective than the broad application of vinegar. Am attaching a monograph about the use of sulfur for lowering soil ph.

Lowering_Soil_pH_with_Sulfur.pdf 153.02 kB · 0 downloads

So, now some pics.

When we started our farm development in 2007 we brought in a Cat D9 to clear the brush, move the 4 to 6 inches of top soil and break up the underlying layers of lava down to about 3 ft depth. Then smoothed out the surface and replaced the soil. We did this on the whole parcel except for 1 acre that had ancient Hawaiian rock walls and terraces that we wanted to preserve.

 

In the 1 acre that we preserved, there was at best 1 inch of organic debris then pretty much solid lava. In the first 2 pics you can see the guys using a jack hammer in 2010 to make holes for the palm plantings. Following is a picture of the same area today.

 

This is a Royal palm in 2010, planted as a 1 gal size in 2008. You can see how rocky the ground is and our plentiful use of mulch.

This is the same spot today.

 

2010 - Very rocky environment

Same spot today.

 

2010- Very rocky environment

Same spot today.

 

2010- Very rocky environment

Same spot today.

 

Hope something here is encouraging and helpful - gmp

 

 

Lovely reply, so informative. It seems that I had the wrong idea about rocky soil. I'll do a soil test and if its too alkaline I'll add sulphur systematically. 

@Phoenikakias gave me a great idea to drill holes and fill them with sand to improve drainage in case the soil is pure impenetrable rock. Let's see.

Btw what are those two trees in the background in the 7th photo?

Edited February 5 by Than

[Phoenikakias]

56 minutes ago, Than said:

Lovely reply, so informative. It seems that I had the wrong idea about rocky soil. I'll do a soil test and if its too alkaline I'll add sulphur systematically. 

@Phoenikakias gave me a great idea to drill holes and fill them with sand to improve drainage in case the soil is pure impenetrable rock. Let's see.

Btw what are those two trees in the background in the 7th photo?

Actually fill in should ideally consist of larger particles than sand but I assume that granite or lava  would be too expensive, sandstone is fragile and of course peebles from the quarry are out of the question, as they are full of lime. It is essential that you check soil pH and drainage capacity. Clay is anything else than ideal draining material, much more in a plain, which receives a lot of precipitation for the Greek standards. I am in a slope, with an uber rocky soil and yet I wish I had better drainage during rainy, winter days. Best gardens are created, where radical soil manipulation takes place before initiation of planting. If soil is alkaline and you decide to go down the path of amendment with sulfur, better do it before planting and depending on degree of alkalinity, you may need up to three years.

[Dr. George]

1 hour ago, Than said:

Btw what are those two trees in the background in the 7th photo?

Young Monkeypod trees (Samanea saman) - gmp

[Than]

3 hours ago, Phoenikakias said:

Actually fill in should ideally consist of larger particles than sand but I assume that granite or lava  would be too expensive, sandstone is fragile and of course peebles from the quarry are out of the question, as they are full of lime. It is essential that you check soil pH and drainage capacity. Clay is anything else than ideal draining material, much more in a plain, which receives a lot of precipitation for the Greek standards. I am in a slope, with an uber rocky soil and yet I wish I had better drainage during rainy, winter days. Best gardens are created, where radical soil manipulation takes place before initiation of planting. If soil is alkaline and you decide to go down the path of amendment with sulfur, better do it before planting and depending on degree of alkalinity, you may need up to three years.

Three years..hmmm.. I'm too impatient for that. Can't I add the sulphur gradually after planting?

[Merlyn]

@Than you can always add smaller amounts of sulphur later, as part of decomposing compost, sulfur-rich fertilizer, sulfur pellets or powder, etc.  But adding large amounts could screw up the nutrient absorption of your plantings, or even kill some stuff if there's too much at once.  If you are planning on using a contractor with a bulldozer or tractor, they can mix in (amend) your top foot or so of rock with topsoil/mulch when leveling things back out.  Another option is to start out with palms and plants that tolerate (or prefer) alkaline soils, like Copernicia and Archontophoenix.  I have acidic sandy soil, so take my comments as just a guess.   

[redbeard917]

On 2/3/2024 at 3:05 AM, Phoenikakias said:

Concrete is good, if you want blue leaves in some spp! One Californian used to plant concrete chunks in the root zone of Brahea plants in order to enhance blueness of the foliage!! (Seriously) You can also plant Thrinax, Coccothrinax and Pseudophoenix as perennials. (not seriously). 

Is it too cold there for Pseudophoenix? Seems like a good choice in a limestone substrate.

By the way, palms in general perform so well with restricted root zones that people have experimented with, and had success, planting them still in the pot. Just search this site for pot planting. So I wouldn't concern myself with that. Further, amending the soil is fairly easy to do and a necessary prerequisite for successful gardening in most cases.

I find the idea that someone would position themselves as an expert, look at some dirt, and then claim to know what was under it very suspect. If he has the power of X-ray vision he could probably make a lot more money in industry or government. You should just dig down and see what you encounter. Any pics of the place?

[Jim in Los Altos]

Most palms are fairly adaptive. These palms are growing on less than 1 foot of soil on top of a solid concrete patio beneath it. Really just about 8-10” of soil. I recently opened up the area a few feet away and added more soil so the palms will eventually have more root space but you can see how well they’ve done with very little soil depth up ‘til now. 
 

[Than]

11 minutes ago, redbeard917 said:

Is it too cold there for Pseudophoenix? Seems like a good choice in a limestone substrate.

Ηοw so? I couldn't find any such info. I bet it is too sensitive as it is only found in Haiti. 

 

27 minutes ago, redbeard917 said:

By the way, palms in general perform so well with restricted root zones that people have experimented with, and had success, planting them still in the pot. Just search this site for pot planting. So I wouldn't concern myself with that. Further, amending the soil is fairly easy to do and a necessary prerequisite for successful gardening in most cases.

Oh I am not so concerned about palms; their root systems are small so I can easily amend the soil around them. I am concerned about other trees and shrubs.

 

28 minutes ago, redbeard917 said:

I find the idea that someone would position themselves as an expert, look at some dirt, and then claim to know what was under it very suspect. If he has the power of X-ray vision he could probably make a lot more money in industry or government. You should just dig down and see what you encounter. Any pics of the place?

I know, right? I am also curious. Tbh he sounded the most honest of all contractors I spoke to. You're right though, I will talk to him and ask him to explain how he could tell without digging. I am curious to hear what he'll say.

[Than]

17 minutes ago, Jim in Los Altos said:

Most palms are fairly adaptive. These palms are growing on less than 1 foot of soil on top of a solid concrete patio beneath it. Really just about 8-10” of soil. I recently opened up the area a few feet away and added more soil so the palms will eventually have more root space but you can see how well they’ve done with very little soil depth up ‘til now. 
 

Every photo of yours is a treat for the eyes Jim! 

How about other trees, not palms? Do they cope too?

[Merlyn]

@Than Psuedophoenix Sargentii is surprisingly cold hardy, I have a couple of young ones (1-1.5m tall) that went through 25F with frost and took no damage.  A good reference for this is kinzyjr's compiled spreadsheet of cold damage reports.  It's a handy way to look up a palm and see if it's got a chance at your location.  You can find the latest sheet in his thread here:

Keep in mind that these are observations based on single cold events, and not necessarily a true measure of hardiness.  But, for example, if you routinely get 30F with frost...then that rules out a large number of palms.

[Than]

41 minutes ago, Merlyn said:

@Than Psuedophoenix Sargentii is surprisingly cold hardy, I have a couple of young ones (1-1.5m tall) that went through 25F with frost and took no damage.  A good reference for this is kinzyjr's compiled spreadsheet of cold damage reports.  It's a handy way to look up a palm and see if it's got a chance at your location.  You can find the latest sheet in his thread here:

Keep in mind that these are observations based on single cold events, and not necessarily a true measure of hardiness.  But, for example, if you routinely get 30F with frost...then that rules out a large number of palms.

Florida's hardiness and ours cannot be compared. My climate is similar to North California's

[Merlyn]

@Than yeah, a cool and wet winter might kill a lot of palms that are otherwise hardy into the 20s.  I see a few reports on Psuedophoenix Ekmanii in CA, lots of Sargentii in FL, but the only Sargentii report outside FL was aztropic's dozen in Arizona.  That might not be too similar to your climate either.  My winter enemy is usually frost.  🥶

[Jim in Los Altos]

4 hours ago, Than said:

Every photo of yours is a treat for the eyes Jim! 

How about other trees, not palms? Do they cope too?

Thanasis, Thank you! It really depends on the type of tree. Some will tolerate shallow soil, some won’t. It would be beneficial and pleasing to the eye if you could create contouring (mounding) of your garden’s planting areas. That would give you more soil depth in areas as well as create a more natural appearance. Multi-level gardens are usually more attractive than flat ones. 

Edited February 5 by Jim in Los Altos

[Than]

9 hours ago, Jim in Los Altos said:

Thanasis, Thank you! It really depends on the type of tree. Some will tolerate shallow soil, some won’t. It would be beneficial and pleasing to the eye if you could create contouring (mounding) of your garden’s planting areas. That would give you more soil depth in areas as well as create a more natural appearance. Multi-level gardens are usually more attractive than flat ones. 

What material did you use to keep the soil in place on the contours? And how did you hide it afterwards?

[Phoenikakias]

1 hour ago, Than said:

What material did you use to keep the soil in place on the contours? And how did you hide it afterwards?

One thing are raised beds for multiple planting. For idividual mounds there has been special equipment devised (special colars deployed around each plant's base)  which is absent in the Greek market. But if you have clay in the soil, some bricks may do the job, because clay acts as a plaster! Lol

[Than]

4 minutes ago, Phoenikakias said:

One thing are raised beds for multiple planting. For idividual mounds there has been special equipment devised (special colars deployed around each plant's base)  which is absent in the Greek market. But you have clay in the soil, some bricks may do the job, because clay acts as a plaster! Lol

Hmmm, yup I guess I could use old bricks and then plant small plants in front of them to cover them.

Yesterday I spoke with another "expert" who told me the soil on my area is mostly sandy. Good news I guess but I'll only be sure once I do the soil test.