Plants That Grow on Walls
I love the sight of a wall covered in flowers, especially if they are actually growing out of the wall as opposed to being a climber growing against a wall or part of a "living wall" setup such as the woolly pocket system. To me the best displays of plants that grow on walls look as though they occurred naturally without any human intervention. As some of the pictures below show, nature often is the best gardener when it comes to colonising a wall with plants. Nature is also the place to look to for inspiration when choosing plants to grow on a wall. Plants growing on cliff faces and in rocky crevices will usually be at home growing out of gaps in a domestic wall.
It's Not a Hanging Basket!
What Affects Plants Growing in Walls?
Plants growing on a wall are effectively living on a cliff face. They have very little growing medium, may be subjected to windier conditions and will get limited water and this will usually dry quickly, unless yours is a water-splashed wall near a waterfall or leaky gutter, for example.
Wall Material - If the wall is made from limestone or has a lime mortar, then it will be alkaline, so unsuitable for acid loving plants such as the lady fern, Athyrium filix-femina.
Wall Attitude - Which way does the wall face? North-facing walls may be more suitable for ferns such as the magnificently named maidenhair spleenwort. A south-facing wall would suit sun-lovers such as thrift.
Wall Purpose - If a wall is structural, e.g., part of a house, you probably ought to avoid growing plants in it, because if there is space for plants, there is space for damp to get in, and the structure may be deteriorating. On a boundary wall or one held together by mortar with just a few little gaps for planting, smaller plants such as corydalis are best. A dry stone wall gives you the most options for planting; these naturally have a host of gaps between stones, which can make great planting pockets and their open construction allows for thicker stemmed plants such as valerian or foxglove.
How to Make Plants Grow in a Wall
Because the planting spaces in a wall tend to be small, it doesn't work trying to push well-established plants into them. Even if you manage to squish a well-grown plant in place, it will be prone to falling out of the wall from not having had a chance to get its roots into all the crevices.
Instead, start with seeds or very small plants which can then send out roots to establish themselves firmly. Either pop a seed into a marble-sized ball of moist compost and press that into a gap in the wall or sow some seeds thinly in to a seed tray and, rather then pricking them out to grow on in pots, prick them out with a bit of compost attached and slot them gently into the planting gap in your wall. You might find that a palette knife helps you slide them in.
The other method is to plant well-grown plants on top of the wall or in pots right next to the wall and hope they spread or seed themselves into the wall. This can be a bit hit or miss!
Have you grown any plants in a wall?
Good Plants for Growing in a Wall
Plants which naturally grow cliff faces such as sea thrift are likely to tolerate growing in a wall and succulents such as stonecrop, which don't need much water, can work well. Plants with a trailing habit, such as ivy leaved toadflax, are designed for cascading down rock faces or scree slopes and can thrive in a wall.
Alpine plants, which often dislike wet conditions and are adapted to growing in poor soils, are another option as are many wild flowers, such as Welsh poppy, which thrive in poorer soils.
Because it's not practical to change the display of plants in your wall from season to season, it is good to choose plants with long flowering seasons, attractive foliage or which are evergreen so that you get a pleasing display for longer.
As a general rule, plants which have a thick taproot are best avoided because these will grow thicker and may start to make the space it's growing in bigger and eventually weaken the wall. Plants with single stems, such as foxgloves, are best avoided in windy positions because these snap off more easily.
If you want inspiration, a walk around your neighbourhood should provide some with a combination of self-sown wild plants and intentionally sown garden plants growing on walls in your vicinity.
Bell Flower: Campanula
The smaller campanulas are very suitable for growing in a wall, such as Campanula cochlear (fairy thimbles) or Campanula poscharskyana. Both of these produce runners which help them spread along the wall and establish a good show quite quickly.
They will flower from May to September. A downside of these is that the can look quite tatty when the first flush of flowers starts to die away or if there is a spell of heavy wind and rain.
Creeping Jenny: Lisimachia nummularia
Creeping Jenny doesn't so much creep as run. It has trailing stems and short stemmed flowers which don't get badly affected by the wind. You can get a yellow leaved variety "Aurea" which is less vigorous. I prefer the ordinary one as the green leaves and yellow flowers together look nice and fresh growing on a wall.
Fairy Foxglove: Erinus alpinus
The fairy foxglove is also known as summer starwort. It originates from the mountains of Europe and though not native to the UK has escaped from gardens and naturalised. Since it prefers poor soil without much competition from other plants, it hasn't become problem. There are pink, white and crimson varieties which all love growing in walls.
Although it is only a short-lived perennial it seeds freely and will keep the wall covered without further intervention from you once it has established. It does well in full sun and prefers poor soil—hence its suitability for growing in walls.
It flowers from April to August. Whilst it doesn't have the longest flowering season, it does produce abundant flowers which are a very cheering sight.
I was quite surprised to see foxgloves which had seeded themselves in this dry stone wall around a field in Burnley, because they a quite heavy plants and could easily be rocked and dislodged by strong wind. They also like a semi-shaded spot and quite a lot of water. Foxgloves are a good choice if you want to attract bumblebees to your garden.
This particular wall is actually a retaining wall for the field, so rather than being open backed, it is backed by soil and as a result retains a lot of moisture, making it suitable for the foxgloves. It is also east-facing with a hedge opposite, so rarely gets full strength sunshine.
If you are going to try growing foxgloves in a wall a west or east facing aspect is best as is planting them lower down the wall where they will be less affected by the wind. They have quite thick stems and strong roots, so avoid using them in a wall whose purpose is structural.
Ivy Leaved Toadflax: Cymbalaria muralis
Native to Southern Europe, Ivy leaved toadflax has naturalised in the UK and easily colonises walls. It is a perennial which trails gracefully. It has the advantage of a long flowering season from April to November and is very hardy but doesn't become a nuisance.
Visually the leaves are slightly reminiscent of ivy, but it is no relative of that plant. It is part of the figwort family which includes snapdragons (Antirrhinum).
Maidenhair Spleenwort: Asplenium trichomanes
As a fern, maidenhair spleenwort spreads by means of spores rather than seeds. You may need to establish it by buying an adult plant and leaving the soil undisturbed around it allow it to produce spores which will grow into tiny plants that you get then transfer into planting gaps in your wall.
It will grow quite happily in limestone walls or where there has been a limestone mortar used. It is native of the UK and can be found growing amongst the limestone of Lancashire and Yorkshire.
Red Valerian: Centranthus ruber
There are red, white and pink varieties of red valerian. It grows wild in France and Germany and flowers from May to September. Red valerian has naturalised in the UK, but is none the less popular as an easy garden plant for a dry situation.
I think it's a bit heavy looking to work well higher up a wall, but planted below knee height, it can be effective. A plant for a dry stone wall, rather then a mortared wall with small gaps.
Self-Heal: Prunella vulgaris
Self-heal is a good choice for growing in a wall if you want a later-flowering plant. It is a naturally low growing plant whose leaves will flatten themselves against a wall rendering it virtually immune to wind damage. It flowers from June to as late as November. It isn't a particularly showy flower and the violet/blue flowers don't stand out very well against a natural grey stone wall, but it could look more effective against a white painted wall.
Stonecrop: Sedum acre
A number of different sedums, as well as Sedum acre, are known as stonecrop. They are all suitable for growing in walls being a hardy, drought tolerant succulent. Most have yellow or white flowers. The downside is a fairly short flowering season of June-July. However the leaves are quite attractive on their own ranging from greys and creams to green with a red tinge.
I thought the stonecrop looked especially lovely flowering out of the mossy wall, which is an effect that can be replicated at home on a wall which is damp or partially shaded.
Yellow Coryadalis: Pseudofumaria lutea
Yellow corydalis looks very attractive growing in a wall and will flower between May and November. It originated in southern Europe, doesn't like getting too damp and as a garden escape has naturalised on walls around villages in the UK. It's not at all thuggish though, so no need to feel hesitant about using it in your wall.