Troughs or tufa, only?

I have enjoyed some success using Bank Run (Glacial Till) from a quarry about a half mile away.  I saw this technique at the EWSE a couple of years ago in Virginia.  I just set up a perimeter of large stones and filled the middle with the Bank Run.  A few larger boulders in the interior provided an area with some elevation.  I call it my Bear's Grave as it is much too large for a Dog's Grave.

Most plants, I think, are used to the natural soil particle make up of larger aggregates at the surface, and smaller particles as depth increases.  This is not to say that large (or larger) rocks do not exist the deeper you go, but that the air spaces are filled with increasingly finer aggregate.  While I can't say this is always true for alpines, I don't think the opposite is ever true.  Upon further reflection, where soil aggregate is dumped in an individual event rather than gradual, this would be true. (More explanation in post below.)  (Comments?)    This is the first time I have heard of the terms "bank run" and "mine run".  I know what glacial till is like here in Minnesota, a mix of aggregate sizes of mineral base, but is it the same as other places?  Certainly it can be made up of different minerals.  I am baffled by "mine run".

As in any situation, and with just about any plant, the climate will play a big factor regarding how a plant grows and what its needs will be in that particular place.  Changing one environmental factor might be compensated by changing another.    For instance, comparatively better drainage is needed in areas with more rainfall.  So when we read about how others grow a plant, we must adapt it to our situation.  Tufa, or the exacting soil make up that goes into troughs, may be the easy way to success, but not the only way.  Prevailing opinion should be understood, but not necessarily heeded.  I don't really know if there is more than one way to skin a cat, but there is certainly multiple ways to grow just about any plant.

The time when I stop tweaking (or at least thinking about tweaking) soil mixes would be a sad day.  It would mean I have lost my passion for betterment, I am arrogant, or I don't care anymore.

Many times, the secrets of growing certain plants, in my opinion, are just that.  Secrets.  Because they are hard to grow is merely because these secrets have not been found.  In some cases, the "difficulty" is just a myth.  

Okay Charles, I'm not sure if I helped answer you question, told you what you already know or just provided more food for thought.  In any case, I listening for others' viewpoints, too.

Charles asks: "So what is the magic of troughs?  It might be in part a totally prepared soil mix somewhat disconnected from the earth? Or might it be the extra TLC that is likely to be extended to troughs or crevice gardens?"

I have often pondered this question.  I believe it is partly the total exclusion of garden soil that contains pathogens and other organisms that some alpines cannot tolerate.  I have tried to replicate trough conditions in the garden by completely lining a sand bed with thick landscape fabric but I am not convinced that you get the same results as a trough.  Another characteristic of a trough is that it contains plant roots very firmly.  I have noted that some alpines do not like loose soil around their roots, Lewisia cotyledon for example. A third characteristic of troughs is that they deter predators.  In our area slugs are a problem but also larger creatures such as rabbits.

Troughs thus provide a more controlled environment than the open garden but there must be more to it than the few items I have outlined above.

I'm quite intrigued by this, Rick.  Can you suggest some reading on soil formation that I might be able to access to learn more?

RickR wrote:

Most plants, I think, are used to the natural soil particle make up of larger aggregates at the surface, and smaller particles as depth increases.  This is not to say that large (or larger) rocks do not exist the deeper you go, but that the air spaces are filled with increasingly finer aggregate.  While I can't say this is always true for alpines, I don't think the opposite is ever true.  (Comments?)

The geological perspective, given my passing familiarity with it at any rate (the study of soil being, admittedly, not at all a big factor in what I do, as opposed to, say, the mere recognition of soil zones and their implications to the geological history, which is that the presence of a soil is related to a period of exposure), is that the longer a surface is exposed, the more advanced the progress of soil formation... i.e. the more advanced the breakdown of minerals and particles, which would occur at the surface faster than at depth... ?  It all depends on what the exposed surface consisted of to begin with, though - in other words, how advanced was the erosional/chemical breakdown at the time of deposition?  Climate also plays a role, which may be needless to say.
Anyway, it is something I am interested in learning a bit more about, if there are some accessible (internet?) references that you could recommend.

David wrote:

Charles asks: "So what is the magic of troughs?  It might be in part a totally prepared soil mix somewhat disconnected from the earth? Or might it be the extra TLC that is likely to be extended to troughs or crevice gardens?"

I have often pondered this question...

... A third characteristic of troughs is that they deter predators.  In our area slugs are a problem but also larger creatures such as rabbits.

Troughs thus provide a more controlled environment than the open garden but there must be more to it than the few items I have outlined above.

An additional feature of troughs, not yet noted, is the superior drainage provided by a raised planting area that is separated from, and raised above, the level of the soil... I suspect this must have an effect, that would be especially significant in higher-rainfall areas. 

David, unfortunately, over the last 3 years or so, the native jack rabbits have learned that my troughs out along the driveway provide a smorgasbord of early season treats, Draba being a favourite!

Skulski wrote:

RickR wrote:

Most plants, I think, are used to the natural soil particle make up of larger aggregates at the surface, and smaller particles as depth increases.  This is not to say that large (or larger) rocks do not exist the deeper you go, but that the air spaces are filled with increasingly finer aggregate.  While I can't say this is always true for alpines, I don't think the opposite is ever true.  (Comments?)

the presence of a soil is related to a period of exposure), is that the longer a surface is exposed, the more advanced the progress of soil formation... i.e. the more advanced the breakdown of minerals and particles, which would occur at the surface faster than at depth... ?  It all depends on what the exposed surface consisted of to begin with, , though - in other words, how advanced was the erosional/chemical breakdown at the time of deposition?  Climate also plays a role, which may be needless to say.

I did think about this very effect (of exposure time), but only in one situation of many in the alpine environs:  In the case of the relatively loose "rock pile apron/shelf" at the base of high mountain rock peaks, one must think of exposure in terms of millennia.  Assuming these aprons build up over time (from fallen rock for the peaks) rather than individual events, and climatic/erosional/chemical being relatively constant through time, the rocks at depth would have been at the surface just as long as what is at the surface presently, plus the added time under the surface, but still (at least somewhat) exposed to environmental factors that encourage breakdown.

But, when the original soil aggregate was dumped as a whole in an individual event, such as glacial till, I must concur with Lori: here, surface soils would certainly be exposed to the elements vastly longer, and breakdown would be more rapid in the upper layer.  (Thanks Lori, for pointing out my narrow vision.)

I suspect that we are talking about quite different perceptions...
If one is really thinking about soil generation from rock slides off outcrops, I think the time frame is not even millenia but truly the scale of geologic time (within which a millenium is the blink of an eye). 
Correct me if I'm misinterpreting, but I suspect that what you are considering "soil" in the instance of a modern day talus fan is either windblown mineral particles (coming from downslope, and filling crevices between rocks with finer material), or is largely created by the decomposition of plant material over time (starting from the beginning of plant colonization after the glacial recession), rather than actual significant breakdown of rock or even minerals.

Anyway, a fascinating subject and probably far too complex to tackle here!  :)

Agreed on all accounts.  I knew I would have problems without the correct wording.  And too much to wrap my little brain around...

Here in E New England USA we have mostly granite and basalt.  It's clear from observation elsewhere, that even a solid metamorphic sand/mud rock, can internally have no visible change over 200 million years or so.  Limestone and marble, though, can maybe have 2 or 3 mm+ of surface deterioration in 100 -200 years.

Here on my ride home we have road cuts in relatively solid basalt with fissures and surfaces of 50 years age or less.  Sadly these only support Pinus strobus and birch sp. These trees have grown as much as  8 to 14 feet.  There can scarcely be any significant organic matter or deteriorated rock, or so I'd think.  Other than in road cuts, most of our exposed stone does have mats of humus with a few rock type plants, but mostly climax  or second growth mixed forest tree species.

I'm still wondering about growing in tight crevices with added stone dust.  I guess the already accepted use of clay is an option.

Clearly, nothing constructed; is going to approximate natural fissures in bedrock.

Charles Swanson

Just thinking about the past discussion about the source of the magic of troughs.  If isolation from the native soil is an important factor, then one might think that a trough placed on or above asphalt, cement or stone might do better than a trough placed on or above soil?

Seeing how my weeds and weedy garden plants move around, I'm guessing stuff at every level of evolution moves around, though.

Charles Swanson NE Massachusetts

I think the difference, if any, would not be measurable or observable, given the limited contact, if any, of soil inside the trough with soil outside the trough via the trough's drainage holes... so long as the trough was not sitting in a place where water could actually collect and be wicked into the trough (although even that would be very limited).
If the trough was set up on blocks, as often is the case, the nature of the underlying surface should have no influence at all.  I could believe that setting a trough up on blocks may possibly affect the ability of the plants within to winter-over in very cold climates though.