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

[Leiomerus]

I have planted alpines in sandstone, in tufa, in marble stone and in stone that we call in Belgium : 'moonstone', because there are a lot of holes in it.
Most people think it's only possible in tufa, but as you will notice, there are a lot more good options.
Of course, the most crazy option is of course : cobblestone. I think it's the most hard stone there is.

But let's first take a look what results one can achieve in some 'normal' stones :

Of course only pictures of Saxifraga, firstly because I'm very fond of them and also because it is a natural rock loving plant.

1/ Saxifraga 'Cumulus' growing well inside this 'moonstone' (I don't know how it's called in English ?)
2/ Saxifraga 'Red Poll', very happy to have a spot inside a sandstone.
3/ Saxifraga 'Winifred' planted in 2002 inside a little hole in a big marble rock. As you can notice, 'Winifred' loves its rock.
4/ Some Saxes planted in sandstone.

[David Nicholson]

Very effective Leiomerus. You might have seen that Ian Young has had some success planting into old concrete blocks too.

[astragalus]

Very interesting to see how well the sax is doing in marble, which is usually not very porous.

[Leiomerus]

Now some pictures of alpines I'm trying to grow inside cobblestones, even harder stones than marble. That's what my good stone drill (Dewalt drill) told me, because the drill had some trouble when I drilled some holes inside the cobblestones. When I used a smaller size of drill bits it went better.

1/ This is the little rock garden I made, only using cobblestones.
2/ This is a picture of the hole i drilled inside a cobblestone after a day of rain. When it stays dry for a day, the level of the water in the hole drops 1 cm. So, even
    a  hard cobblestone is still a tiny bit porous.
3/ Androsace globifera inside a cobblestone. It's only one rosette, but it had an amazing amount of roots. I managed to put all the roots inside the little hole.
    If you look carefully you will notice an other  little hole I have drilled a bit lower, this hole connects with the one the Androsace is planted in. So the surplus of water     
    can get  away.
4/ Normally I don't do that with my marble stones and it might be hard to believe, but the plants don't bother. Here is a picture of Saxifraga 'Your Song' inside a marble   
    stone when it's raining. This Sax. is growing in a hole with no other connections, it's only a hole 15 cm deep and the surplus of water can only get away because of
    the effect of the wind, the sun or the draining capacity of the marble stone. This Sax. also grows on an almost flat surface. The first year is always difficult, but the       
    plants growing in marble never die, only birds  sometimes like to destroy these little plants.

[Leiomerus]

This is another example. You will see a picture of Saxifraga 'Excellent' from March 2012. This Sax also grows inside a little hole on top of a big marble rock. So it also gets a lot of water. It was planted in Spring 2011.
The second picture is from December 2012.
Compare the two pics and you will also jump to the conclusion that it has grown a lot in only a few months.
 

Although the marble is far from porous, the plants do like to grow in it.

[gote]

Most rock is far from porous. If porosity were a "must" the alpine flora would be confined to very small patches. Most plants will grow very well in granite, limestone or indeed, as Ian has shown, in old concrete blocks. (Fresh concrete would have a too high pH) It is the substrate between the rocks that is important.
Göte

[Leiomerus]

Of course, most people use tufa rock to grow alpines inside a stone. It works very well.
This is why I started this, to prove it is also possible in many kinds of type of stone.
If you walk around in the mountains, you don't see tufa, but other types of rock and full of plants in the cracks and fissures of even hard rock.

Of course it is possible in old concrete too, but I prefer 'real' stones.

[Leiomerus]

Here are some other rock plants I have planted inside cobblestones :

1/ Saxifraga matta-florida, a Sax. that does not produce many flowers. So, let's see if the hard life inside these hard rocks will stimulate this Sax. to take care of some offspring. 

2/ Saxifraga 'Niobe', a nice Sax. which makes a nice cushion with sometimes a few sessile flowers. It's already a 'big' plant, but it hadn't many roots so I managed to squeeze the whole root system inside the little hole. It's always important that all the roots are kept, otherwise it's much more difficult for the alpine to grow inside the rock. Especially the lowest roots, the 'delving' roots should not be damaged. Therefore it's always wise to only plant little alpines inside rock, since they have not yet an extensive root system.
Of course I'm not always that smart.

3/ The last one is a part I detached from a bigger plant of Silene acaulis.
Silene acaulis grows very well in my situation, but no way you will see any flowers. And in the mountains you will see thousands of flowers on it.
Maybe we should deprive the Silene of too much food, starve it a bit. So I planted it in a cobblestone.
I will be very excited when this should work ......

We will notice in a few months if the plants will be happy ..
and me too. 

[astragalus]

You seem to be having wonderful success.  I always think of tufa and I know that the roots will really delve into that rock.  I also grow in crevices, real and man-made, and the rock is not tufa.  With the crevices, though, there is a lot of depth for the roots because the rock (graywhackie) is
quite hard. I've never tried planting in the rock because it doesn't drill well at all.

[Lori S.]

It looks great.   It will be interesting to see how the plants do with time.  If the rock is as tight as it sounds, their root growth will be restricted pretty much to the size of the originally-drilled hole.    As long as the root mass is enough to sustain the plant, I imagine the top growth may be able to spread out across the surface of the rock with time?
The difference with planting in holes drilled in tufa is that the rock itself usually has quite high porosity and permeability such that roots may be able to penetrate beyond the originally-drilled hole and, I suppose, collect some water and nutrients (there can be a fair bit of organic matter trapped in tufa due to its origins, i.e. algal binding of sediment and precipitated calcium carbonate).   It might still be a somewhat restricted environment but in nature, life exists wherever and for as long as it can... 
I agree that planting in crevices though (in nature, these would be along bedding planes and fractures) would give the best opportunity for roots to go as deep as they might want. 
Great experiment!
 

[Leiomerus]

Of course you need a good drill. When I first tried this, I borrowed a Hilti, a professional drill. Of course, I needed a good stone drill of my own.
At first I tempted to drill a hole in marble stone with an ordinary Black and Decker drill. After 10 minutes the Black and Decker was broken. It was still under guarantee, so I got a new one, but I didn't use it for this purpose anymore. 
12 years ago I bought a good stone drill : Dewalt. It  costed at that time more than 8000 Belgian francs, that's now 200 Euro.
But it's really a good one and it still works fine.

You should try it, Astragalus, it's amazing, but it works.
I never had any tufa, I only bought some last year.
Maybe the plants will grow faster in tufa, but I'm not sure. If I compare, there is not a lot of difference.
I also grow a lot of plants in sandstone, and it's much cheaper than tufa.
This sandstone is not that hard, to give you an idea, if you drill a hole in it and you fill it with water, the water will be vanished (or swallowed by the rock) after 10 minutes.

Here some pictures of (of course) Saxifrages in sandstone :

1/ Saxifraga 'Ann Beddall' in sandstone, planted in 2011
2/ Saxifraga 'Your Smile' in sandstone, planted in 2009
3/ Saxifraga 'Peach Melba' in sandstone, planted in 2011
All pictures are from Spring 2012

[Leiomerus]

I do not agree, Lori.
The plants do grow inside the rock, either if it's tufa, marble, cobblestone or sandstone.

All plants only have a restricted room for their roots : 10 cm deep and 0,8 cm wide. But they grow and flower each year more and more.
Just take a look at the picture of Saxifraga 'Winifred'. Its cushion gets bigger every year, if it would not grow inside the rock, it would have starved a long time ago.
This nice Sax. is growing in marble rock since 2002.
They grow inside the rock by using their delving roots with the help of bacteria and fungi, in this way the plants are capable of dissolving the rock and doing so, taking the rock's nutrients.
It's also a fact that plants which are growing inside rocks are much stronger than the ones growing in the open rock garden.

When I plant an alpine inside a little hole in the rock, I use the dust produced by the drill (in fact very little rock particles), I mix it with coarse sand and some fine sand. That's the only medium I put inside the hole I drilled. That's it, no peat or compost. In this way the plants will have to look for nutrients inside the rock.

[astragalus]

This is a fascinating discussion.  You've given a lot to think about and I'll be doing some experimenting this season.  Thanks for starting the topic.  One question - are your drilled rocks in full sun or are they shaded?

[Luc Gilgemyn]

It would be most interesting to hear if Dr Rock (Dave Millward) has any views on this ??

[Leiomerus]

Just do it, Astragalus, you will be surprised. Of course, when you plant a preferably small alpine, you should give it water when it doesn't rain, but only for some weeks. After that the plant should be able to take care of its own.
A long time ago, I think in 1996, I also planted some alpines in this sandstone rock (the same one of which I posted a picture in the beginning, with all those Saxes, now in a better place)  But the stone got sunshine almost all day long and it was not a success. I think the most plausible reason was also that I made the mistake to plant the alpines in a mixture of mostly peat and chippings. Maybe it's strange, but by using peat the plants are initially not stimulated to grow inside the rock. This also means they are more prone to sun burning.

I have planted a Saxifraga marginata in a marble stone, it's there more than 10 years. I never really looked after this one. Never gave it water when the weather was hot, I forgot all about it. Between 2003 and 2009, I had some other hobbies and so I rather neglected my alpines. So they had to take care of them selves.
Talking about this Sax. marginata, this plant is on top of a big marble rock, very exposed and gets all weather elements, including a lot of sun.
After all this neglect, it's still alive and kicking.
Most saxifrages will never get burnt from the sun, as long as they have water at their roots.
Now, if a hard stone like a marble rock, takes up very slowly water, this means that it also very slowly loses its water reserve by evaporation. So, since it rains a lot in Belgium, its water reserve should always be at a good level. This is probably the reason why I have never ever lost a plant, growing inside a marble rock. 
When I say never, I lie a bit, because I did lose plants growing in it, but this was only due to blackbirds who love to play with little plants, especially young ones that are planted only a few months. It also depends on the spot. Some spots are frequently visited by these feathered devils and other places are always left in peace. You never know it beforehand, only by trial and error.

Is there a Dr Rock, Luc ?
Interesting, some people call me Mr Stone.

1/ Here is a picture of that Saxifraga marginata I talked about, its grows together with a splendid yellow lichen. Also a recently planted Saxifraga 'Sissi'.
2/ This is the rather little rock my Saxifraga 'Winifred' is growing in. 'Winifred' is now happy to have the company of a lot more Saxes. Some were planted a few years ago, the lower ones. The others only in 2012. Also an Androsace. The names you will see.
This side of the rock gets only 2 hours sunshine. There I took some precautions.