As millions look forward to Bank Holiday in the garden, there is rising concern about one of the most popular horticultural products.
The sector agreed the voluntary deadline with government eight years ago because harvesting the ingredient for compost is environmentally damaging.
The programme’s findings have led to fresh calls for a legally-enforced ban on peat sales.
The gardening industry has responded with a new pledge to reduce peat sales, giving consumers more environmental information in future.
Footage for ITV Tonight shows large scale peat production continuing this summer in Ireland, as agricultural vehicles remove it from land where it has taken centuries to form.
UK garden centres are the biggest market for Irish producers.
As peat goes from bog to bag, the production process destroys a unique habitat and releases greenhouse gases.
Peatland is one of the most efficient “carbon capture” environments, preventing carbon dioxide reaching the atmosphere.
The ITV investigation reveals no major garden centre chain has yet completely stopped selling peat and that “reduced peat” compost can still contain up to 90%.
James Barnes, the chair of the Horticultural Trades Association which represents garden centres, said: "I think in all honesty the 2020 target will be very difficult to reach."
He said by introducing reduced peat compost the industry has achieved a 56% cut over recent years, but he admits more is needed.
Now the gardening industry is to launch a new labelling scheme giving more detailed environmental information.
Mr Barnes told ITV Tonight: "I think we need to make strides to make that clear. What we are hoping to launch later this year is a responsible sourcing scheme ... to inform the consumer what is in a bag of growing media."
Some campaigners reject the garden industry's voluntary efforts at peat reduction and now want a legal ban.
Dr Catherine O'Connell of the Irish Peatland Conservation Council described peat extraction as a "total disaster".
She told ITV Tonight: "I'm very disappointed that peat sales continue in UK garden centres.
"We now need clear leadership from the top and a legal ban is the solid way forward."
The UK government responded to the programme's findings saying it is "working with the horticultural sector to overcome barriers to going peat free" and is "considering further measures".
The Trouble with Garden Centres? - Tonight is on ITV on Thursday 22 August at 7.30pm