TALES OF PLANTS FROM THE URBAN CRACKS AND CREVICES: HOW YOUR WALLS BECOME A PLANTS FAVOURITE HOME


 

Have you ever looked at a crumbling brick wall or an old stone fence and noticed tiny plants growing out of it? 

No soil, no garden bed, just a few cracks, some moss, and suddenly there’s a whole ecosystem clinging to the masonry.

It’s not just poetic, it’s botanical brilliance.

In this post, we’ll explore how plants manage to grow on vertical, seemingly inhospitable surfaces like walls, and what it tells us about plant survival, urban ecology, and nature’s incredible resourcefulness.

Walls Are Not as Barren as They Look

To us, a brick wall or concrete structure may seem hard, dry, and lifeless. But to a plant, it’s a world of tiny opportunities.

Walls offer:

- Microhabitats in cracks, mortar gaps, and surface textures

- Moisture retention in shaded or porous areas

- Protection from ground-level competition and some herbivores

- Wind-dispersed seed catchment (especially near ledges)

Even a few millimeters of accumulated dust, moss, or decaying organic matter is enough to germinate seeds.

Step-by-Step: How Plants Take Over Walls

Dispersal

First, seeds have to arrive. This happens through:

- Wind (e.g., dandelions, ferns)

- Bird droppings (seeds from berries)

- Water runoff

- Insects or ants

- Gravity (falling from nearby vegetation)

Many wall colonizers produce tiny, lightweight seeds designed for long-distance travel.

Germination

Once a seed lands in a crack or crevice, it needs:

- Moisture

- A bit of substrate (dust, sand, organic debris)

- Light (though some shade-tolerant species thrive in dim spots)

Some plants have adapted to germinate in shallow soil or bare rock, using minimal resources.

Root Infiltration

The roots begin to explore the surface, anchoring into:

- Mortar gaps

- Weathered stone

- Natural fissures

These roots secrete acids and enzymes that can gradually break down minerals and widen crevices, especially in porous stone like limestone.

Growth and Expansion

Once anchored, the plant:

- Grows upward or outward, following the surface

- Collects rainwater and dew

- Photosynthesizes from even partial sun exposure

- Accumulates leaf litter, creating more micro-habitat

This creates a mini ecosystem sometimes supporting insects, fungi, and even mosses and lichens.

What Types of Walls Support Plant Growth?

Different wall types offer different challenges and opportunities:

Wall Type

Colonization Potential

Notes

Old stone walls

High

Porous, often cracked, ideal for mosses and ferns

Brick walls

Moderate

Mortar gaps allow root entry

Concrete

Low (but possible)

Harder, smoother, but cracks can support mosses or small ferns

Dry-stone walls

Excellent

No mortar, full of gaps, and rich biodiversity potential

Walls exposed to weathering (rain, sun, frost) are especially likely to support plant colonization over time.

Why This Matters: Plants as Urban Pioneers

Wall-dwelling plants are part of a larger process called ecological succession. It is the natural progression from bare surface to complex ecosystem.

In cities, these pioneer species:

- Add greenery to grey infrastructure

- Provide microhabitats for insects and birds

- Capture dust and CO₂

- Cool surfaces through transpiration

- Slow down water runoff

They’re the quiet rewilders of the urban landscape.

Common Traits of Wall-Colonizing Plants

Wall plants tend to be:

Trait

Example

Small & compact

Ferns, mosses, succulents

Drought-tolerant

Sedums, wall pennywort

Shallow-rooted

Annual herbs, certain grasses

Clinging or trailing

Ivy, maidenhair fern

Tolerant of poor soils

Almost all pioneer species

Some even exhibit crassulacean acid metabolism (CAM), which is a water-saving photosynthetic process common in succulents.

Final Thoughts from the Biolab desk

Walls may not seem alive, but they are. Over time, nature finds its way, often seed by seed, crack by crack, until even the most unyielding surfaces host green life.

Understanding how plants colonize walls isn’t just a curiosity. It sheds light on plant adaptability, urban biodiversity, and how resilient ecosystems can take root in the most unexpected places.

So next time you walk past a weathered wall with a fern poking out of the mortar, take a moment to appreciate it, not just as a weed, but as a survivor.

What are some of the places you have seen plants grow on walls? Let us know in the comments.


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