Lithic Multch : using rocks.

I ran across this while reading Collapse : How Societies Choose To Fail Or Succeed, by Jared Diamond.

In marginal dry, windy areas such as Easter island and the American south west, the natives were using rocks as mulch. The rocks decreased surface evaporation and effect soil temperatures. In some cases increasing crop yield quite a bit. I saw no reference on permies.com to lithic multch. I felt compelled to post it.


Some googling :

http://www.solar783.com/solar783/1317.pdf
http://www.bahs.org.uk/44n2a4.pdf
http://www.springerlink.com/content/x7725npp48626482/
http://weltanschuuang.blogspot.com/2008/08/lithic-mulch.html
http://www.earthwatch.org/images/Pdfs/.../05_stevenson_freport.pdf

This is quite cool, I've used rocks around new fruit trees for suntraps per Holtzer reading. If I had enough gravel I'd try this, I know the Eden fella used stones as mulch too. I use large rocks, I wonder about the different beneficial characteristics.

The native folks in Maine use rocks in their three sisters. When they create a mound for planting the squash, they place stones in the bottom of the rounds. The extra heat from the thermal mass is supposed to quicken germination. I tried it last year. But did not have a control plot to contrast the results.

Karin Schott wrote:The native folks in Maine use rocks in their three sisters. When they create a mound for planting the squash, they place stones in the bottom of the rounds. The extra heat from the thermal mass is supposed to quicken germination. I tried it last year. But did not have a control plot to contrast the results.

I can attest to the rocks hastening germination. I had two areas for raised beds last year. One was lined with stones and the other was lined with some pine logs. I had greens and squash in both beds amongst other things. The bed lined with stone germinated faster and grew faster. The stone bed also had collards that made it all the way to December before freezing to death. And the roots lived through the winter and already have a small bunch of leaves now. The bed lined with pine died off in early November and nothing survived the winter.

While I'm not native, I am living on the midcoast of Maine. Stones are easy to come by here.

I think another thing worth considering about rock mulch is that by reducing absorbent surface area you get better water penetration when it does rain. It also removes the impact of rain on potentially bare ground, removing the chance of loss of soil which can become hydrophobic after prolonged periods of drought. Another factor that I believe would be of most interest to investigate would be the potential for the rock, over time, to leech out mineral nutrient into the soil itself. I know generally that it is proven that rock dusts provide a huge benefit to soil fertility, I just wonder whether the interaction between soil microbiota and the surface of the rock would also have that potential.

In reference to the pine logs, think part of the issue there would be how new the logs were, their potential for raising soil acidity, and the tendency of wood to remove nitrogen from the soil. Better to do the hugelkultur thing and bury them under a good layer of soil, manure, mulch and plant them out the following year.

There are two major drawbacks to rock or pebble mulch.

First, rocks and shovelfuls of pebbles are heavy.

Second, in researching pebble mulch I found that long term use of pebble mulch causes a depletion in soil nutrients because the mulch does not allow organic material to be integrated into the soil (though my experience with stone and gravel mulch in landscaping shows that windblown dirt and leaves will create a rich soil in between the stones, creating a thriving weed bed, if you are unwilling or unable to use weed killer -- or chickens). With power equipment, you could probably move the lithic mulch around easier, but it would still be tedious and somewhat expensive to clear your beds every one to three years to incorporate compost and/or fertilizer.

Liquid fertilizer and compost tea could be used, though I haven't found any research to show how effective it would be.

It may be wise to put in aerating soil amendments that will not break down over time, such as charcoal, expanded clay and shale, etc., before covering with lithic mulch.

I have used pebble mulch in small beds to good effect in the dry climate I live in. I gave it up when my back started to go. I could have used it with my container garden this Summer. I often needed to water the pots more than once a day, when the humidity was below 10%, the temperature was above 95 F, and the wind was blowing. I will try it next year.

I don't know how effective gravel sized expanded clay or shale would be as mulch, since it is porous. It would certainly be easier to move around, but you can't get it for free.

Water is so expensive here that a large garden is a luxury. It is often cheaper to buy vegetables at the grocery store. Any way to reduce water consumption is worthwhile.

spray some lichen on the rocks, the ones that have blue grey algae associated with them are nitrogen and co2 fixers too.

prob wont have to dig to add more biologics if you do that and have added biochar soaked with manure tea as foundation soil.

Just today I was moving some rocks out of the small paddock where I keep small piglets (till they outgrow it or escape). I notices lots of earthworms under the rocks and was trying to decide what it meant.

This area has a very thin layer of topsoil and it has been raining quite a bit of the last few weeks. Maybe the worms were just getting out of the weather?

Picking rock is a regular post tilling job around here. Many folks have helped ends meet by this odd job. I found myself unpicking out of a 100 year old pile. Maybe in another 100 years we'll have put them all back where we found them.

Worms under rocks, get moisture, and shielding from a hot surface, plus birds can't get through their armour casing.

Ludens talked about this often in his Texas garden; I surprised he didn't pop in yet.

Its use I feel is best for low organic soils in the semi-arid and arid regions of the world.

The Anasazi lived by this method with Agave species for sometime.

In general a slow, high producing low input plant seems best; Agave, Enset, & Cordyline.

Another poster already mentioned the downsides to this; in the right conditions and maintance however its use could be very useful.

Another downside to rock mulch is that is rather rapidly sinks into the soil and, in this dirt, creates a barrier almost like concrete. I have a section of my property that used to be a gravel driveway (greater than 50 years ago) but has about 4" of dirt on top now from erosion. Only a few hardy weeds and grasses will grow there, and their roots don't penetrate the rock layer. Forget digging there with a shovel; I've tried. It would require a mini-ex.

Also, getting the rocks out later on is nearly impossible. Whenever I use rocks (like in my creekbed), I put down a porous but sturdy barrier like weed cloth that keeps the rocks on top. Dirt and weeds still collect on top, but you have a little assistance when it's time to remove the rocks.

Now mind you guys do realize the size being talked about; at first I thought they meant pebbles and at most golf ball size; turns out fist size at the smallest is what's being talked about 8-o

James Slaughter wrote:I think another thing worth considering about rock mulch is that by reducing absorbent surface area you get better water penetration when it does rain.

Are there some sources for this? I'd like to read more about how that works.

Thank you,
Bryan

Hmm.. looks like I'll be covering my hugel beds with rocks! Solar gardening is awesome sauce.

Bryan, doesn't the Easter Island reference in the first post say the opposite about rainwater penetration? I am guessing that there are a lot of variables that need to be addressed when considering lithic mulch. What works in one area may not work in another (and what doesn't work in one may work in another).

Use of cobble mulch augments, traps, and retains available runoff moisture, elevates nighttime temperatures, and decreases soil erosion.

http://www.fs.fed.us/rm/pubs_rm/rm_gtr272/rm_gtr272_181_188.pdf

M Troyka wrote:

Use of cobble mulch augments, traps, and retains available runoff moisture, elevates nighttime temperatures, and decreases soil erosion.

http://www.fs.fed.us/rm/pubs_rm/rm_gtr272/rm_gtr272_181_188.pdf

Thank you. It makes a lot more sense now, there are more crevices for the rain to fill as the rocks do not pack as densely as finer materials.

The document appears to be filled with conjecture, as are the documents referenced in it, but then they are archaeological studies . It also mentioned that lithic mulch is usually found in conjunction with sandy soil.

There is a Chinese (or Indian, I can't remember for sure) experimental study of lithic mulch, but it is behind a pay wall (very pricey, if I remember correctly).

Moving gravel and stone is hard work. If I were you, I wouldn't commit to extensive use until it is proven to work in your area. If you are going to experiment, start with something small like containers or a small bed. Do your soil amending and fertilizing before you cover it. It might work well with underground soaker hose and liquid fertilizer.

As I mentioned earlier, I have used it in small beds and it does seem to help with my soil and climate conditions, but I cannot move the gravel around anymore.

I have only a couple areas of rock mulch, where there are cactus, rosemary, agave, hesperaloe, and sotol. I have a lot of rock piles for erosion control and critter habitat, but not using rocks much as mulch, definitely not in the vegetable garden.

yes, this seems right to me, regardless of understanding the specifics. i think maybe theres some other stuff that happens in the synergy of rocks and plants that arent apparent to humans.

i have always sensed that the plants LIKE the rocks around =) and always used rocks on top and bottom.

they are even sort of tied into how i garden. like if i go out with a fork to loosen up a bit, theres some re arranging of the rocks...and once the rocks are rearranged right i am done. i dont know if thet makes sense, but it works for me, without thinking bout it too much -they somehow help out =)

I found a bit more info on rock mulching, and it turns out there is a disadvantage to it. A layer of rock mulch, as it was used in the US Southwest, prevents organic material from being effectively returned to the soil. Or, at least laying down organic mulch on top of rock mulch negates the benefits of the rock mulch, and lifting up the rocks after every harvest to lay down the crop residues would be a ridiculous amount of work. As a result, rock mulching led to long term soil loss.

http://www.persee.fr/web/revues/home/prescript/article/quate_1142-2904_1998_num_9_1_2107

I came up with an interesting solution though. Someone mentioned using a rock border around raised beds and got clearly superior results, so I figure you could use rock borders to protect the sides of hugelkultur and improve the performance. Use big rocks to anchor the bed in place, then use small rocks to fill in the spaces between the big rocks. Organic material/crop residues can still be added to the top of the bed, while the rocks should improve the temperature and microclimate, improve water absorption by stopping water from running down the sides, and protect the pile from erosion by water and from drying by wind. Of course, this would only work if you built shorter, more round-ish beds like what I have rather than 6 foot tall pyramids like Sepp does. I'm pretty sure that building tall beds like that would only increase wind exposure and thus dry the beds out faster, and a tall bed would be a nightmare to rock mulch against the wind.

Nutrient depletion was/is also a problem in China and other locations. A compost tea might be the way to get nutrients back in the soil without scraping the mulch off every two or three years.

I remember seeing in one of the photographs of the lithic mulch beds in the South West US, that lithic mulched beds alternated with open beds.

Why would you be using lithic mulch in Georgia? Don't you have plenty of organic mulch available?

I think the lithic mulch referred to in Collapse, was for temperature. From memory, the lithic mulched gardens were up on hills where it got quite cold in winter, and perhaps wouldn't support crops otherwise.

Well, originally I was going to cover the beds with rocks, but after further reading I've decided to use them just as a border and to reinforce the sides of the hugel beds.

The main reasons for using rocks:
1: Sometimes we get heavy rain here, which flows around my beds and can erode the corners especially badly. Some big rocks ought to fix that.

2: Sometimes we get light rains, and the rocks around the edges stop the rain from falling straight off.

3: The rocks around the edges can increase the moist area of the hugel beds, so that they store more water overall, and prevent drying by wind so they stay wet longer.

and

4: The rocks should store a lot of heat and block wind near the ground, and should extend my growing season, possibly to 365 days.

Organic mulches can only do maybe half of those things, probably not quite.

I am using rocks in my hugel culture beds and I have made a few observations:
-If you make small beds and use rock mulch it will compress the bed. If you build large beds and use rock mulch there is less compression because the angle of the bed wall is more vertical.
-Plants germinate a lot faster and more profusely around rocks mulches.
- If you place rocks on only one side of the raised bed ( the south facing side) and create gaps in the rock mulch for organic mulches there should be no issue with the addition of organic matter to the soil. Plants growing near and between the rocks will get organic matter from nearby organic mulches, roots, and the organic matter building on the other side of the bed.

though i wouldnt lay down a legit "mulch" of small rocks suc as convevtional landscapers do, i think that stacks of rocks and scattered stones can cause immense benefit to the system they are in
as for landscaping sized pebbles i think i shall like to try pourig them into a cylider of chicken-mire or some such to allow air to flow through and condese in the pillars that have been created

Using smooth and flat ~6 inch river rock just inside a raised bed, up against the frame, creating a 6 inch wide strip around your veggies, works very well. Is easy enough to move twice a year, when applying a heavy mulch Growing a carpet of clover, such as Dutch or New Zealand, works extremely well, in my limited experience

M Troyka wrote:

I came up with an interesting solution though. Someone mentioned using a rock border around raised beds and got clearly superior results, so I figure you could use rock borders to protect the sides of hugelkultur and improve the performance. .

Large rocks work excellent here in Zone 5 to absorb heat during the day then release this heat during the evening - creating a microclimate. Peppers do not like chilly nights and are one crop I use rocks for. Also, it is important to shield heat-loving plants from the cold north wind, that blows in from time to time.

http://www.youtube.com/watch?v=SUnH57a8ASU