“We’d sold out of porridge oats and muesli by lunchtime and fusilli pasta is getting low,” said Tor Harris, pointing to the rainbow-like row of 28 vertical perspex dispensers filled with dried foods from red lentils to pumpkin seeds and quinoa.

Harris, head of corporate social responsibility for Waitrose, was striding the aisles at the store in central Oxford to gauge customers’ reactions to the first day of the upmarket grocer’s most groundbreaking green initiative to date, aiming to reduce unnecessary packaging and single use plastics.

“The idea is to find out how far our customers are prepared to shop in a completely different way and just how far they will change their behaviour,” she said.

The shake-up – part of an 11-week trial – starts at the store entrance, where the cellophane wrap has been removed from all flowers and indoor plants and replaced with 100% recyclable craft paper and fibre-based pots.

For those who have arrived unprepared for the opportunity to ditch all conventional packaging, reusable plastic containers are for sale ranging from tiny pots to 3.6-litre food canisters.

The store offers reusable cotton bags for fresh fruit and vegetables. Photograph: Alecsandra Raluca Drăgoi/The Guardian

In the fresh fruit and vegetable section, packaging has been removed from 160 lines – 75% of Waitrose’s fresh produce offering. Dozens of lettuce heads spill over a display, like a market stall. Pak choi, mangetout and spinach are piled high. Customers can put them in compostable bags or reusable cotton bags. Soft fruits and tomatoes, which are vulnerable to damage, are contained in cardboard punnets.

At the back of the store is the refill station – where customers can bring in their own containers, tubs and jars to stock up on dried goods – with a 15% saving on the packaged alternative. Containers are weighed separately and the price is then calculated and printed on a barcoded sticker for payment at the checkout.

Four different wines and four beers are available on tap to take home in reusable bottles.

Customers can also grind any of four coffees to take away, while a large freezer contains loose frozen fruit. Ecover washing up liquids can be bought from a refill fixture.

Waitrose chose Oxford for the experiment, according to Rachel Edmonds, the company’s customer proposition manager, “because it is a large and busy store, and one where we know there is a wide range of different shopping styles – everything from a major weekly shop to popping in for the ingredients for the evening meal.”

Customers will be asked for feedback on the retailer’s website, Twitter and Instagram and the findings will determine which of the ideas will be rolled out to other stores.

The vegetable section looks like a market stall, with lettuce heads spilling over wooden boxes. Photograph: Alecsandra Raluca Drăgoi/The Guardian

Customers were curious about the changes, and having heard about the initiative on the radio or from their newspapers, had arrived with their own containers from home.

Hundreds of hand-written notes had been posted on to two noticeboards that asked for suggested improvements. “It would be better if cider was on tap,” read one.

Pam Matthew, who lives nearby in Cumnor Hill, bought a bag of pumpkin seeds for £1.55. “I’d normally have to buy a much bigger bag than that, when I don’t need very much. I like the refill idea, but I’m a little bewildered by it and it is a bit time-consuming. Until I get used to it all it’s going to take me longer to do my shopping.”

Claudia Reed, an accountant from Poland, said she was an instant convert. “It’s all very easy to use. We have refill systems back home in Poland and it makes so much sense” she said, weighing her bag of frozen blueberries, which cost 50p per 100g. “It’s greener and cheaper.”

Christine Jacques, who was shopping with her daughter Katy, said she was more sceptical. “I think it’s going to take a long time to get used to. It actually feels quite old-fashioned. But it’s a matter of learning as you go along.”

The supermarket has pledged to remove black plastic – the one used for microwave meal trays – from all its own-brand products by the end of 2019, and recently launched the world’s first home compostable ready meal packaging.

Environmental campaigners welcomed the initiative. Daniel Webb, of the campaign group Everyday Plastic, said: “Offering less packaging through refill initiatives at major supermarkets presents a massive step towards reducing the amount of plastic being thrown away. Let’s cross our fingers that other supermarkets will follow.”