Planting alpines in marble stone or even cobblestone - Am I crazy ?

[Maggi Young]

Is there a Dr Rock?

Oh yes!   Dr  David Millward is a geologist. Many posts in the Forum and articles in the main SRGC Website:
http://www.srgc.org.uk/monthfeature/content.html "Land of the upside down Tulip"  in two parts
and for the Rock Garden, the IRG  and , and    ....



Alpine Plants: Ecology for Gardeners

By John E. G. Good and David Millward
Alpine Plants: Ecology for Gardeners explores ecosystems above the treeline on mountains and beyond the treeline in sub-polar regions from a gardener's perspective. It looks at the effects of geology and soils, low temperatures, precipitation, drought, and snow on the morphology and life cycles of alpine plants — including perennial herbs and grasses, annuals and biennials, prostrate and dwarf shrubs, bulbs, and cushion plants. Armed with an understanding of how plants function in these extreme environments, gardeners will be able to tailor their cultivation practices in lowland gardens to mimic the alpine habitat as closely as possible. A concise introduction to the science behind the success of alpine plants, this fascinating and accessible book is an invaluable complement to more plant-focused references.


http://www.timberpress.com/books/9780881928112   

[Leiomerus]

Hmmmm, maybe it should read this .....
I might become a bit less crazy.

[Leiomerus]

I do not only plant saxifrages inside my marble stone, here are some pictures of other plants :

1/ Androsace hirtella x (of course not the real one, mostly you get hybrids between Androsace hirtella and cylindrica)
    Although this high alpine requires a lot of drainage, it feels fine without it. It grows inside this marble rock in a single hole I drilled, about 10 cm deep. The growing         
    medium consists of the leftovers from the drilling job, coarse sand and crushed shells. Normally the birds are fond of this Androsace, but for now, they leave it alone. I   
    seem to have found a good spot for it. When the sun shines in summer, the Androsace gets about 7 hours of sunshine. Of course the slope of the rock tends towards
    the east.

2/ I also recently planted an Asperula sintenisii, I think it will feel good inside its marble rock.

3/ I can't end without a Saxifraga : this is Saxifraga bryoides planted to enjoy a cobblestone.

[Leiomerus]

Now a Sax. I planted this summer inside a beautifully coloured marble stone. Sometimes I think I'm rich, there was a time that only rich people owned marble in the form of stairs or a mantelpiece. I have more than 50 tonnes of marble stone, so I call myself rich. Lol. 
Of course, I use it for other purposes.

Here is Saxifraga 'Jaromir', I will be amazed when it will flower, for it's rather a big Sax, but you never know .....
Anyway it will make a nice hard cushion on this rock. The cushion will absolutely be hard, it's a hard stone after all.

[Leiomerus]

A Sax. that is also always nice for the cushion alone is Saxifraga paniculata minutifolia.
So, it also deserved a place to live inside a marble rock.

[DaveM]

Sorry for not replying sooner to Luc's "challenge", but things have been hectic here lately. References to DrRock remind me of some colleagues of mine on the staff of the Geological Survey here in the UK from the 1980s and 90s, by the name of Drs Rock, Stone and Basham - yes really, I'm not making this up!! Drs Rock and Basham were both petrologists, and Dr Stone a field geologist like myself.

Leiomerus, this is indeed a fascinating experiment. I hope you will continue to keep us posted on how the plants perform in the longer term.

I'm not sure that commenting on the rock types you have from the photographs will be very reliable but I shall try anyway. I know of no rock called moonstone here in the UK. This name is usually reserved for a semi-precious "stone" used in jewellery where moonstone is the mineral adularia (one of the feldspar group of minerals, that is: sodium potassium aluminium silicate). The rather knobbly and 'holey' appearance suggests to me that this is a limestone. The weathered surface of many limestones show such holes as a result of dissolution of the rock by the slightly acid rainwater. Such crevices in limestone areas are a distinct habitat for all sorts of small plants, including bulbs.

Some of the other rocks you have also seem to be a limestone. The name marble is used in the stone industry for a wide range of rock types, many of which are not made of calcium carbonate. In geology marble refers to a limestone that has been metamorphosed deep in the Earth's crust.
By contrast, the rocks in which you have Saxifraga matta-florida and 'Niobe', and Silene acaulis for example are igneous - you can clearly see the crystalline character of these. Both of these rock types will have almost no porosity and therefore will not allow water to flow through their mass. Water will only flow in these rocks both when the rock is fractured and that the fractures form an interconnected network. Such fracture crevices are a major site for alpine plants in the wild.

This is very different from tufa, a freshwater limestone. As has been said this is often highly porous - but very importantly the pore spaces are interconnected, allowing root penetration and water to be drawn through it by capillary action. Pumice (a volcanic froth) has a similar interconnected structure and ought to be a similarly good growing substrate: unfortunately it is not easy to obtain large blocks unless you live in a volcanic region.

I was interested in your comment that your sandstone block drains well. It seems likely here that the rock has many tiny, interconnected pore spaces between the sand grains - you can see small holes on the surface; any "open" fractures would enhance the water flow. So, in a sense the structure of your sandstone is superficially quite similar to that of the tufa and pumice.

So in summary, we have two quite separate groups of rocks - those that have interconnected porosity and those that are impervious without fractures. Intuition says that the former ought to perform well in the garden whereas I'm not sure about the latter, particularly over the longer period. There is plenty of good evidence that alpines will grow well and live for long periods in tufa and, by extension in your porous sandstone. But do remember that not all sandstones have pore space.

One particular concern is with those plants in the impervious rock - the plants seems to be doing well whilst they are young and small. However, Saxifrages like many alpines have a huge root system compared with the growth above ground. Growth of the root system will be severely restricted as there is no space for the roots to penetrate the rock unless it is fractured. What will happen to the plant as it gets older - will it maintain good health and flower power or will it gradually dwindle?? So please do keep us posted.

[Luc Gilgemyn]

Many thanks Dave ! 
A much appreciated scientific look on things.  I'm sure Leiomerus and many others will be very interested !

[Tim Ingram]

Soft sandstones do sound good possibilities in the absence of being able to locate tufa - I wonder how they get colonised with plants in the wild, even in the absence of fractures? I suspect that the crevice garden is always going to be the most effective way to grow a lot of plants in the long term because of the extensive root systems that Dave refers to - surely only lichens and maybe mosses (in very wet places) are likely to grow for really long periods on 'hard' rocks?  I would have thought holes would need to be drilled right through to the substrate below if plants were really to establish.

[Leiomerus]

Thanks for the appreciation, Mr 'Doctor Rock'.
Of course I will experiment further with planting alpines in 'hard stone', there's no doubt.

Thanks for the information about the stones.

Here is mine : the 'moonstone' is indeed a type of limestone, I already knew that the holes in this limestone are created by acid water, which dissolves the softer limestone. The harder limestone is left with a lot of holes in it.

The marble stone is indeed the result of the enormous pressure executed on deep buried limestone by the earth above it. This way a hard limestone is created.
Ideal for lime loving plants like saxifrages. At least, that's what I think.

The cobblestone or I rather think it's porphyry, should be igneous. That's why I planted Silene acaulis, Androsace vandellii, Saxifraga bryoides and Sax. 'Niobe' inside these.
These plants all love rather a more acid medium than lime.
Now I know for sure it's igneous, thanks for that.
Of course these are the hardest stone's there are, but they do have some porosity.
I did an experiment and drilled a hole in this cobblestone. Than I filled it with water.
After a day the water had dropped 1 cm, this means the stone had swallowed some water. It was only 5 degrees Celsius when I did this, so it was not by evaporation.

My sandstone is much appreciated by the plants (and by me). It surely has an open structure, but not as open as tufa. When you poor water on tufa, it's away after a few seconds, whereas this sandstone makes the water disappear in ten minutes.

Now some explanations about the plants. High alpines are adapted to grow inside rocks, in cracks, in little holes. But by doing this, they also grow inside the rock where they have found a home. Of course, these high alpines have not much food, when they grow in a rock. They make a cushion, and the old leaves, on which the new leaves grow, are used by the plant as food and also as a water reserve. Most of the energy comes from the sun, so the plant can also grow through fotosynthesis. The rest of the food the plants needs, is taken from the rock it grows in. The plants roots even will penetrate the hardest rock. This they perform in symbiosis with the little creatures that live en masse on their roots : bacteria and fungi. With the help of these, plants can grow inside rocks. The roots of plants in combination with bacteria and fungi do dissolve rocks. To explain it in a very simple way : bacteria get carbon from the plants, the bacteria produce acids when they digest the carbon, these acids help to dissolve the rock. A bit like bacteria that make nice holes in your teeth when you eat candy (or sugar or carbon)
I have written a whole explanation on this topic at my website : www.rots-plant.be

Of course, I'm not a scientist, but that doesn't mean I'm not interested in this matter.
Not everything I write can be true, but a great deal is true, I believe, especially because of the things I see with my own eyes.
I do like to experiment and I think I already have proven that for instance saxifrages can prosper several years growing inside a little hole of a big, hard rock.

You already saw Saxifraga 'Winifred', this one is planted in 2002 inside a 'moonstone' and inside a marble stone. That's more than 10 years.

These are all pictures from today : full of promising buds and as healthy as can be :
1/ Sax. 'Winifred' in 'moonstone'       11 years
2/ Sax. 'Winifred' in marble              11 years
3/ Sax. 'Your Song' in 'moonstone'    I think more than 15 years
4/ Sax. 'Excellent' in marble             3 years 

 
 

[Maggi Young]

After a day the water had dropped 1 cm, this means the stone had swallowed some water. It was only 5 degrees Celsius when I did this, so it was not by evaporation.

I don't think it needs to be very warm for there to be evaporation of liquid. There will be some wind, perhaps and that can also cause water loss, don't you think?

[Tim Ingram]

Leiomerus - it is certainly impressive to see that you have plants over ten years in limestones, and it will be encouraging to try something similar (although it would be really nice to use tufa!) - I suppose in a way it resembles gardeners growing bonsai, so long as there is moisture available and a small amount of nutrient they will grow very slowly. The 'proof is in the pudding', but scientifically the important way is to compare different methods of growing plants; and Nature must provide the best examples, so I still think cracks and crevices with deeper root run will be more successful. Even though stone will be slowly broken down, this occurs very slowly, more in geological time, and plants naturally are adapted to easier situations.

What would be really interesting would be to plant up similar sized blocks of different materials (like this block of tufa) and compare how plants develop over long periods. It certainly looks as though some of the stone you have used can be very effective, and I'm not sure many gardeners would ever thought of using them. There are also good examples from years ago in the AGS Bulletin of gardeners using 'Hypertupha' very successfully, and there must be great opportunities to play around with these ideas.

[Leiomerus]

I don't think it needs to be very warm for there to be evaporation of liquid. There will be some wind, perhaps and that can also cause water loss, don't you think?

This week I will drill another hole in this cobblestone, fill it with water, cover the hole with a plastic bag and a stone, so no evaporation can take place.
Then I will see if the water level drops or not. 

[Leiomerus]

Thanks Tim.
Of course, the more nutrients and space for the roots a plants has at its disposal, the better it will grow.
But alpines are sometimes a different matter.
There are some rock plants I lost over the years, but luckily I still had some growing inside a stone.....

I'm already comparing the results of the same plants (mostly Saxes) growing in different type of stone.
For instance, I have Saxifraga 'Cumulus' growing in my sandstone, in marble, in the limestone with the holes (what we call 'moonrock' in Belgium) and in tufa.
Saxifraga 'Your Song' I have also growing everywhere.
I have already compared Saxifraga 'Jaromir'. One in marble and one in tufa, planted at the same time.
The one in the marble looks the best for now.

The experiment with the cobblestone is only going on for three months, so I can't  see the results yet. Therefore you certainly need a whole year.
I planted 2 little plants of Androsace vandelli inside a hole in this cobblestone, this is a plant which needs a lot of drainage and in this hole they get none.
After 3 months one is dead, because of too much water, I also planted it a bit too deep,  but the other one stills looks very good.
I already planted an extra one to replace the one that died.
We will see what the future brings.


Hypertufa is a stone that you can make yourself, I suppose ?

[Tim Ingram]

Yes - 'hypertupha' was described by Fisher way back in 1936 - a mix of Cement (1part), sand (1 part) and Peat (2 parts), all by volume. It is much more used for covering old glazed sinks (or making sinks) than for actually casting 'stone', but Fisher showed a nice example of it planted up in a trough after five years, with saxifrages and sempervivums and it looks very effective.

He used a box of fine sand and a range of good jagged pieces of stone to make moulds to cast the 'tupha', and there must be a lot of gardeners who have tried this since. There are many more recent descriptions but I don't think many gardeners have actually shown examples of plants growing after quite a few years, and these would be really interesting.

[gote]

One has to be little careful when dealing with materials bound by portland cement (yes the "portland" is often dropped) The pH is initially very high. Too high for plants. Fortunately this extra alkalinity is eventually neutralized by carbon dioxide in the air and water. I would be worried about growing directly in hypertufa that has not been aged long time enough. A through covered by hypertufa would be less of a problem since the high alkalinity would be restricted to the interface between the container and the compost.

Aerated concrete (Thermalite, Durox, Celcon and that ilk) is porous and has connected pores but also that has a pH that is too high for plant life. Again: it can be neutralized by carbon dioxide.

It is possible to neutralize using other acids than carbon dioxide but the result tends to be disintegration of the binder.

I would buy a roll of the type of paper that shows pH by changing colour and test before using any of these materials unless properly aged (meaning years).

Good luck

Göte