The Gardened Wall - Alpines at the Edge

[Tristan_He]

I've mentioned to this in some posts before but I thought it might be interesting to bring some of this together and try to explain what I've been doing with / to some of my plants! I live in a cottage in the hills of North Wales, and quite a bit of our garden has walls of various types and standards of construction. I've wondered about what sorts of plants could grow in these conditions. Lately green roofs and green walls have been quite in fashion, but the types of plants grown in these have been quite unadventurous (Sedums and er.. more sedums). So... I have been playing around with my own walls. Here they are:



This is a dry-stone boundary wall with mortar cap and coping at the top. It was raised about 3 years ago to make it sheep-proof. Although south-facing the lower, older part gets a good bit of shade from the house and has a good coating of mosses. The north face is not really cultivatable sadly as there is a nettle-bed, and it would be accessible to sheep grazing. I'll call this the heath wall.



Self-sown Polypodium and moss on the heath wall.



We also have a ruined outbuilding that we have capped off to stabilise it. This is also dry stone I think but with a strong vertical face. It's sunny and faces west, so gets the full force of the prevailing weather.



I'll call this the road wall. It is the boundary wall that runs north-south, then does a right-angled turn to run east-west before doing another shorter north-south run. This wall is mortared so no opportunities for alpines there (should have thought of that when we built it...). But there is a deep slate coping on top which provides lots of potential crevices.



Finally this is the boundary with next door. It's a pretty rough bit of stonework - I think about the best you can say is that it hasn't fallen down. However, it faces north and is shady, so lots of potential niches. I haven't really done much with this yet but the polypody seems to like it.

Obviously this is an extreme environment. To start with there isn't any soil. Some needs to be provided, but then again many alpines in the wild seemingly grow with minimal soil anyway, in tiny crevices in boulders or even among mossy cushions. I didn't have the luxury of building soil in with the walls (and I'm not sure if this is really a good idea anyway, too many weed opportunities). There will also be extremes of temperature and water. So... what survives, what thrives and what dies? And how do you establish plants in an environment where it's difficult to get soil into cracks, and which is really difficult to water?

[Tristan_He]

At the tops of the walls, the copings are an obvious place to start. The heath wall copings are fairly shallow:



But the slate copings on top of the road wall are deeper. Even so, there is only room for an inch or two of soil.





Houseleeks (Sempervivum) are an obvious choice in this environment. I've lost the label for this one but I think it might be an S. calcareum clone. It's a good doer. The poor soil helps them develop a good colour. I used garden soil for this and you can see there is a volunteer primrose in the background! Also a few celandines have popped up, though they don't flower.



S. 'Sprite' is a favourite of mine.



I can't remember what this one is. There is a label but it is buried and I'd have to pull apart the plant to find out! Anyway, it's a nice tight cushion.

[Tristan_He]

Here are some more plants on top of the road wall.



Veronica sp. prostrata - thanks Trond! This was here when I bought the house and should really have found out what this is by now. It seems to like the wall and stays more compact than elsewhere in the garden. You can see Sedum anglicum in the background - unfortunately this is rather a nuisance as it has seeded liberally into the rockery below. S. reflexum, album and spurium are all doing fine as well, not surprisingly.



Geranium cinereum, again nice and compact in this sunny nutrient-poor location. I thought it might suit Erodiums too but they have mostly died.



A Lewisia cotyledon hybrid has not done too well either. It is surviving but not really growing or flowering.



Globularia meridionalis is growing, but rather slowly and hasn't flowered this year. I'm hopeful it will do something though. Maybe I will give it a weak feed to encourage it.


This Campanula cochlearifolia is from seed I collected last year, and I was quite surprised to see it flower already. Hopefully it will establish.

[Tristan_He]

Dianthus 'Whatfield Magenta'. This seems a good place for pinks, the white unidentified 'not superbus' that I posted earlier in the year on another thread also does well here. However, it is a bit too dry for D. deltoides which shrivelled up during a dry spell in June. It has perked up again now but does seem to struggle a bit.



I have also planted some spare seedlings of D. pavonius in among the coping.



Saxifraga sp - I'm not very careful with labelling pieces that I tear off but I think this may be cochlearifolia?



Sedum sexangulare.

[Hoy]

Tristan,

a very exciting project! Seems you have found several suitable plants already. I can recommend several of the silvery saxifragas. Here they seed in the thin moss cover of rocks and stones. They also like mortar. (Maybe the Lewisia dislike too much Calsium?)

Saxifraga cotyledon do not need much soil, just a crack or a thin layer of moss is enough.



Small ferns like Aspleniums do very well in such walls. Also sea thrift will grow there. They are best planted as small seedlings!

[Maggi Young]

Brilliant idea to  start this thread, Tristan!  Thanks!

[ashley]

I second that Maggi.  As a lover of plants in stone walls I'm fascinated to see your experiments and results Tristan

Here in Ireland many villages and rural communities like to participate in a 'Tidy Towns' competition.  Unfortunately this may include 'tidying up' old stone walls by removing vegetation.  Ironically this reduces the charm of old bridges and similar structures built with soft mortar that could be colonised over time.  More serious harm is done by spraying glyphosate on our traditional ditches (earth banks faced with stone, widespread in Ireland) which depended on plant roots for stability and therefore begin to collapse

Could your Veronica sp. be officinalis, the heath speedwell?

[Hoy]

I go for Veronica prostrata

[Tristan_He]

The great thing about this kind of garden is that there is virtually zero maintenance. Weeds don't really seed into it and if they do, growth is slow and they are easy to remove. Slugs don't make it to the top and it's not necessary to worry about drainage or watering (at least once the plants are established). Planting is more of a challenge however! I wedge in a couple of stones at the end of the crevice to help stop soil washing out.

[Tristan_He]

Hi Trond, I think this is my Sax cotyledon (or a hybrid of it). It's on the heath wall and definitely seems to like it! The Lewisia looks a bit underfed to me, maybe I just need to give it a weak feed. What is the Campanula in the background of your photo? I think this environment could be quite good for saxatile campanulas, not as many slugs.



Also thrift is a great idea, I'll collect some seed when we go to the beach.

[Gabriela]

Yes, this is an exciting thread Tristan and I think everyone can contribute a bit to it and maybe help you with the plants choices.
I find a great similitude between your stone walls and the alvars habitats from Ontario, especially the shoreline alvars. It is fascinating to watch plants growing in thin rock fissures on just tiny amounts of sediments/moss.
Campanula rotundifolia does very well there, accompanied often by other species like Primula mistassinica, Viola nephrophylla, Packera, a dwarf Solidago and so on....

And as you just mentioned, there is no weed competition in these tough situations

[Tim Ingram]

Campanula rotundifolia, to which Zdenek Zvolanek replied with - "I like this mighty circus of walls" - when I put this picture at Malham Cove on Facebook. They do really well in the sand bed in our garden, seem to grow on nothing!

[Tristan_He]

C. rotundifolia is a lovely thing isn't it? We don't grow it enough in gardens, I suppose as the saying goes, familiarity breeds contempt. There is a nice patch along the road not too far from here, I always mean to collect seed.

'A mighty circus of walls' is a brilliant description of Malham Cove - a bonkers landscape that looks as though it cannot possibly be natural.

I've put a couple of pieces of Campanula pulla on the top of the wall today, the rain will help water it in.

[Tristan_He]

Ashley, I agree, very sad how some people feel the need to 'tidy' everything.

'Tidy Towns' always makes me laugh. In Britain we always seem to give things grandiose or impressive sounding names - Royal this and that, or Britain in Bloom. Ireland is so much more down to earth.

[Tristan_He]

Gabriela, had never heard of alvars, just Googled them. They look fascinating, perhaps worth a thread in their own right?