Su Kahumbu Stephanou’s passion for soil health is deeply personal. Her journey into this field began with a harrowing experience over two decades ago.
“In 1999, my mother and I were tending to tomato plants on our farm. The plants had a pest problem, so we decided to use a pesticide. While spraying, my mother suddenly became very ill from the toxic chemicals. Thankfully, she recovered, but that was the last time I used pesticides,” Su recalls.
“Although I didn’t know it then, pest infestations are often a symptom of poor soil health. Weak plants attract pests like an open dinner invitation.”
This realisation became the cornerstone of Su’s advocacy for healthy, living soil.
From farmer to educator
In 2000, Su expanded her organic farming business by working with smallholder farmers to meet the growing demand for organic produce. She also began writing for The Organic Farmer magazine to share her knowledge.
By 2003, she had opened Africa’s first organic retail store, The Organic Shop, in Nairobi. But she soon realised her passion lay in teaching rather than trading.
“I wanted to empower farmers with knowledge, not just supply them with products,” she explains.
Recognising the challenges farmers faced—degraded soils, poor yields, and climate change—she launched iCow in 2010. This mobile agricultural platform delivered timely, actionable knowledge to farmers, even those with basic mobile phones.
Freshly harvested vegetables at Su Kahumbu’s kitchen garden in Karen, Nairobi on January 18, 2025.
Photo credit: Billy Ogada | Nation Media Group
Despite these efforts, persistent problems such as pest infestations and soil degradation persisted. When the Covid-19 pandemic struck in 2020, Su seized the opportunity to deepen her understanding of soil science. She enrolled in the Kiss the Ground Soil Advocacy Course and Dr Elaine Ingham’s Soil Food Web School.
A new understanding of soil
“Soil is alive,” Su emphasises. “It teems with bacteria, fungi, protozoa, and nematodes that play a crucial role in plant health. If we destroy this life, we undermine the foundation of agriculture.”
Her first experience with soil microscopy was transformative. Inspired by what she learned, Su launched the iCow Soil Advocacy Programme, a five-week virtual course that has trained hundreds of students across Africa.
The programme began with a unique group: 30 boda boda riders who were trained to educate women in their communities about soil health. Today, the course has reached students from 28 countries.
Su is now Kenya’s first certified Soil Food Web Lab technician and is working to establish Africa’s first soil microbiology services and a digital soil and BRIX lab platform. Her goal is to provide smallholder farmers with affordable, science-based solutions to improve soil health.
Why soil health matters
Healthy soil is the cornerstone of sustainable agriculture. Rich in organic matter and microbial life, it produces resilient crops that resist pests and diseases without synthetic chemicals.
Beetroot at Su Kahumbu’s kitchen garden in Karen, Nairobi on January 18, 2025.
Photo credit: Billy Ogada | Nation Media Group
“Healthy soils create nutrient cycles, ensuring plants have access to the minerals they need,” Su explains. “They also sequester carbon, retain water, and prevent erosion.” Living soils support the growth of nutrient-rich crops, which are more profitable for farmers and better for consumers.
Common challenges and solutions
One of the biggest challenges farmers face is a lack of knowledge about soil health. Many current soil tests focus solely on chemistry, often recommending synthetic chemicals that harm the soil microbiome.
In Kenya, for example, over 60 percent of soils are acidic due to poor practices that have decimated the microbiome.
“Healthy soils are essential to prevent the collapse of civilisations,” Su warns. She advocates for practices like bio-complete composting, minimum tillage, and planting cover crops to regenerate soil.
For home gardeners, Su recommends keeping soil covered with living plants, using mulch, and avoiding tillage. Simple tests like water infiltration and soil integrity can help assess soil health.
“A clod of soil that stays intact in water indicates good microbial aggregation,” she notes. “These small steps can make a big difference.”
A vision for the future
At 60, Su’s mission is clear: to transform agriculture from the ground up. Through education, she hopes to empower farmers and young people to restore degraded land and combat climate change.
“If we want to heal the planet, we have to start with the soil,” she says. Her work is about more than agriculture; it’s about securing the future of food systems and the planet itself.
Her message is simple yet profound: soil is alive, and by caring for it, we can heal the Earth.