Lava Rock Mulch rich in micro-nutrients, but too Acidic?

[Mauna Kea Cloudforest]

I've always heard that the Hawaiian islands have very acidic soil, which makes it difficult to grow palms like brahea. Is that because of the lava based soil? I've been using red lava rock to mulch a lot of my palms. My concern is to use it with palms that like calciferous soils. Does lava rock change the soil pH to acidic?

Apparently, lava rock is chuck full of nutrients, so it's going to be of tremendous benefit to palms. But if it's acidifying, it would be a problem. See the video below on the nutrients aspect:

I have not been able to find any references in regards to pH. but I wonder if the improvements seen in the video are actually due to pH changes as opposed to micro-nutrients.

I've used it on a brahea super silver, and it seems quite a bit more unhappy now.

[Dypsisdean]

My understanding - although not researched or confirmed (just my understanding of chemistry) - is that Hawaiian soils are acidic because of two factors. 1) the absence of the abundant salts and minerals like limestone that are alkaline and/or basic and only present in the soils of older continents 2) and because of abundant rainfall and virtually no lakes or rivers that run over and/or collect all these disolved solids, there is no buffering ability in the water to counteract the acidification that all the decaying plant material imparts to the soil.

For example, SoCal soils are so high in pH because of a lack of organics, a lack of rainfall, and abundant mineralized salts - especially from irrigating with Colorado river water which runs over limestone deposits for great distances and is very high in pH and TDS.

In other words, I don't think lava rock affects pH much at all, it would have to dissolve in water for that to happen - especially when compared to all the other factors. It is used as filters in ponds and fresh water tanks - so I doubt it affects pH much at all.

[Mauna Kea Cloudforest]

My understanding - although not researched or confirmed (just my understanding of chemistry) - is that Hawaiian soils are acidic because of two factors. 1) the absence of the abundant salts and minerals like limestone that are alkaline and/or basic and only present in the soils of older continents 2) and because of abundant rainfall and virtually no lakes or rivers that run over and/or collect all these disolved solids, there is no buffering ability in the water to counteract the acidification that all the decaying plant material imparts to the soil.

For example, SoCal soils are so high in pH because of a lack of organics, a lack of rainfall, and abundant mineralized salts - especially from irrigating with Colorado river water which runs over limestone deposits for great distances and is very high in pH and TDS.

In other words, I don't think lava rock affects pH much at all, it would have to dissolve in water for that to happen - especially when compared to all the other factors. It is used as filters in ponds and fresh water tanks - so I doubt it affects pH much at all.

Thanks dean, that's exactly the answer I was looking for. The mulch works well for keeping the soil moist and provides additional soil warming as well. If it adds micro nutrients, it's even better. And it looks beautiful. So if it doesn't change pH the. It's even better.

I am going to replant the brahea, I'll surely find out what the issue is.

Any comments on the video from anyone?

[rick]

That video is a prefect example of a little bit of knowledge used the wrong way. Yes it is true that plants need trace elements and lava rock contains trace elements BUT this guy's experiment is so fundamentally flawed that the results are meaningless. First only having 2 plants gives no statistical power. For all we know the lava rock plant may be a naturally more robust grower. Anyone that's grown a tray of seedlings has seen that some plants just grow faster than others even in the same conditions. Second he only gave the plants 2 weeks. Im not an expert on geology but I would think that the amount of minerals that could be dissolved out of the rock and absorbed by the plants would be infinitesimally small in that amount of time. Even if we are to assume that the rocks are providing enough trace minerals the rocks only have a limited supply of them so the rocks would eventually need to be replaced at a great cost. Third the video was posted in on april 28th of this year. Im assuming then that it was filmed in march or april. Those are one of the driest times in south florida. Those cacao trees were fairly large and would require a large amount of water. The lava rocks, as he acknowledged in the video, acted as a mulch which helped the pot retain more moisture than the unmulched pot. Since the benefits of mulch are well known and proven to be effective, a real control would need to have used some other type of mulch. This by itself most likely accounts for the bulk of the differences seen. Also if you look at the two plants when he first started the lava mulched plant had slightly larger growth to begin with. As far has the whole putting diluted sea water on the plants you can read up on why homeopathy is worthless.

Axel for your purposes I think the rock would be of benefit to warm the soil and retain that heat at night as well retaining moisture. Over time the rock would break down and release trace elements but they would be minute compared to a single application of a good fertilizer with trace elements.

[Mauna Kea Cloudforest]

That video is a prefect example of a little bit of knowledge used the wrong way. Yes it is true that plants need trace elements and lava rock contains trace elements BUT this guy's experiment is so fundamentally flawed that the results are meaningless. First only having 2 plants gives no statistical power. For all we know the lava rock plant may be a naturally more robust grower. Anyone that's grown a tray of seedlings has seen that some plants just grow faster than others even in the same conditions. Second he only gave the plants 2 weeks. Im not an expert on geology but I would think that the amount of minerals that could be dissolved out of the rock and absorbed by the plants would be infinitesimally small in that amount of time. Even if we are to assume that the rocks are providing enough trace minerals the rocks only have a limited supply of them so the rocks would eventually need to be replaced at a great cost. Third the video was posted in on april 28th of this year. Im assuming then that it was filmed in march or april. Those are one of the driest times in south florida. Those cacao trees were fairly large and would require a large amount of water. The lava rocks, as he acknowledged in the video, acted as a mulch which helped the pot retain more moisture than the unmulched pot. Since the benefits of mulch are well known and proven to be effective, a real control would need to have used some other type of mulch. This by itself most likely accounts for the bulk of the differences seen. Also if you look at the two plants when he first started the lava mulched plant had slightly larger growth to begin with. As far has the whole putting diluted sea water on the plants you can read up on why homeopathy is worthless.

Axel for your purposes I think the rock would be of benefit to warm the soil and retain that heat at night as well retaining moisture. Over time the rock would break down and release trace elements but they would be minute compared to a single application of a good fertilizer with trace elements.

Rick, you hit the nail on the head. I thought two weeks was also rather short. I use it for moisture retention and heating the soil but not as snake oil to make my palms grow. It does generate a lot of dust so over time (many months) it should add some trace minerals but not enough that I would stop using palm fertilizer.

As you suggest, For pots it might also help with heating and moisture retention.