Slowly he explained how he had seen the weather change: seasonal rains have turned to seasonal floods and dry spells have become droughts in recent years around the village of Kibweze.
"But I don't think it's my fault," he added, shaking his head.
Yet the softly spoken farmer finds his small plot in rural Kenya at the centre of a storm over climate change.
Environmentalists are putting pressure on western supermarkets to reduce imports of fruit, vegetables and flowers from Africa.
They are keen to reduce the amount of carbon dioxide pumped into the atmosphere by the cargo planes that transport the produce.
Now the Kenyan horticulture industry is fighting back. It is trying to win over ethical shoppers by spelling out the environmental and ethical benefits of buying green beans and mange-tout from Africa.
In a country where two-thirds of the population lives on less than 50p a day, the chance to grow fashionable vegetables for British supermarkets has helped lift many farmers out of poverty.
Mr Muyu is typical. His earnings have rocketed since he signed up with a company - which is backed by the charity Care - that sells his aubergines and baby corn to British supermarkets.
He has more than doubled his income since switching from maize and onions.
"There's been a big difference," he said. "Now I have to have a proper system of farming but I can send my children to school."
He has earned enough to invest 20,000 shillings (150) in a small shop run by his wife.
The signs of the village's new-found prosperity are everywhere.
Two banks have opened branches and shiny new bicycles fill the dirt tracks that criss-cross Kibweze.
Vegcare, the company which collects the produce and sells it on to Britain, estimates the trade is worth more than three million shillings (23,000) a month to the village.
George Osure, general manager of the Vegcare operation in Kibweze, which lies about 140 miles from the capital, Nairobi, said shoppers in Britain needed to know how their purchases were helping develop African communities.
"The consumer is aware of the transport and air freighting but there are other things," he said.
"We are creating a socially responsible farming community. Their children go to school, they pay their workers on time and they are careful about any chemicals they use on their farm."
But the farmers of Kibweze are under threat from the British environmental lobby.
The Soil Association, which certifies organic food in the UK, is reviewing its policy on air-freighted produce.
The organisation is considering withdrawing its organic stamp from all produce flown in to Britain from abroad.
Several supermarkets, such as Tesco and Marks & Spencer, have already tried to reduce their carbon footprint by labelling air-freighted flowers, fruit and vegetables with an aeroplane logo to allow customers to decide. But the impact of a reduction in trade could be huge.
Fresh flowers, fruit and vegetable make up two-thirds of exports from Kenya to the European Union, according to the Fresh Produce Exporters Association of Kenya.
Half of this goes to British supermarket shelves and is worth 100 million each year to the country's economy. The trade supports about 135,000 jobs.
To protect its farmers, the Kenya flower and vegetable growers associations is launching its own label, with a design based on the sun.
Its "Grown Under the Sun" campaign is designed to show that Kenya's fruit and veg are produced with little in the way of artificial inputs.
For now, said Romano Kiome, permanent secretary of Kenya's agriculture ministry, African farmers are in danger of being shut out of the globalised marketplace.
"I do not question the desire to improve local trade but in our globalised world one should approach this in a manner that takes into account issues of fair trade.
"Discriminating against air-freighted produce amounts to protectionism through the back door," Mr Kiome said.
'FOOTPRINT' FIVE TIMES SMALLER
THE Kenyan industry says it is plain wrong to assume that importing from Africa is any worse for the environment that buying tomatoes which are grown closer to home.
Farmers like Mr Muyu simply cannot afford the fertilisers, pesticides and artificial lighting and heating used in Europe.
The result is that flowers which grown in Kenya have a carbon footprint five times smaller than those grown in heated European greenhouses, according to Erastus Mureithi, chairman of the Kenyan Flower Council.
"Some of the communications and the inadequate labelling that has been introduced encourages people to draw conclusions which simply aren't true," he said.