GROWTH AT THE CRACK OF THE WALL: HOW ROOTS FIND THEMSELVES THROUGH YOUR WALLS, PAVEMENTS AND ROADS



Plants growing on walls may seem like a botanical paradox. I mean, how can delicate roots possibly penetrate stone, brick, or concrete? 

Yet, many species do exactly that, defying the odds and turning seemingly inhospitable vertical surfaces into thriving green pockets.

You tend to see this happen in the roads we drive on, the pavements we walk on or even sometimes, the edges or corners of our houses compounds.

So without further ado, let us explore the fascinating mechanisms roots use to infiltrate hard surfaces, the science behind their persistence, and the consequences for both plants and structures.

The Challenge: Growing Where There’s No Soil

Unlike garden plants rooted in loose, nutrient-rich soil, wall plants must, find tiny crevices and gaps to anchor, extract moisture and nutrients from minimal substrates and overcome mechanical barriers like dense stone or mortar.

Their roots don’t just grow, but they also engineer their own habitats.

Chemical Root Weathering: Nature’s Tiny Rock Breakers

Roots aren’t passive. They actively secrete organic acids (like citric and oxalic acid) and enzymes that chemically dissolve minerals in stone and mortar. This process is called biochemical weathering.

If you are interested in learning more about weathering, check out the article by National Geographic below.

National Geographic cover on weathering

It helps roots expand cracks and access deeper layers and over time, this leads to the gradual breakdown of rock, contributing to soil formation.

Some root-associated microbes and fungi enhance this process by producing additional acids or enzymes.

Mechanical Force: Roots as Natural Wedges

In addition to chemistry, roots exert mechanical pressure. As roots grow thicker, they physically wedge apart tiny fissures, even a tiny root can generate enough force to pry apart brittle mortar or soft rock.

This repeated growth cycles (root thickening and shrinking with moisture changes) can progressively enlarge cracks.

This combination of chemical dissolution and physical pressure makes roots formidable wall invaders.

Root Adaptations for Wall Life

Wall-rooting plants often display special traits:

Adaptation

Purpose

Thin, flexible roots

Navigate tight crevices

Root hairs

Increase surface area for water/nutrient absorption

Symbiosis with fungi (mycorrhizae)

Enhance nutrient uptake in poor substrates

Ability to enter dormancy

Survive dry periods in harsh microhabitats

These adaptations maximize survival where conditions are tough.

Impact on Walls: Friend or Foe?

Ecological Benefits

- Roots contribute to biodiversity by creating microhabitats.

- Aid in soil formation on vertical surfaces.

- Help retain moisture, benefiting other organisms.

Structural Risks

- Root growth can weaken mortar joints, accelerating wall degradation.

- In older or poorly maintained structures, roots may cause cracking or displacement.

- This can increase repair costs and safety concerns.

Balancing appreciation for these plants with structural preservation is key.

Examples of Wall-Rooting Plants

Some common species known for their root ingenuity include:

Plant

Notes

Ivy (Hedera helix)

Roots cling tightly, penetrate mortar

Maidenhair spleenwort (Asplenium trichomanes)

Fern with delicate root system

Wall pennywort (Hydrocotyle spp.)

Shallow roots, spreads over surfaces

Sedum spp.

Succulents with shallow roots, drought-tolerant

These species showcase different strategies for rooting in tough spots.

Final Thoughts from the Biolab desk

The ability of roots to penetrate stone and mortar reveals nature’s incredible resourcefulness and persistence. Through a combination of chemical weathering and mechanical force, plants engineer their own living spaces and turn walls into vertical ecosystems.

Understanding these processes helps us appreciate the delicate balance between nature and human structures, reminding us that life finds a way, even where we least expect it. What are some of the places around your region that you have noticed roots growing the hard surfaces? Let us know in the comments

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