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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!
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