Ethical Consumer Research Association (ECRA) report author Katy Brown said that while garden centres can play an important role in making a positive environmental contribution, from growing your own to wildlife gardening, private investment firms with "less-than-clean ethical records" are spoiling the green image of many centres.
Tesco-owned Dobbies scored 0/20 in ECRA's "ethiscore" table, while Sir Tom Hunter-owned Wyevale scored just 5/20. Focus scored 7/20.
The research looked at company owners' policies on environment, animals, people and politics. Areas such as policies on animal testing, ethical supply-chain policy, ethical environmental reporting and ethical use of habitats and resources scored poorly.
Dobbies, Wyevale and Focus scored badly for "anti-social finance" - because they are owned by Tesco, WCC (a Hunter investment vehicle) and Cerberus Capital Management respectively.
Use of peat, rainforest timber, abuses of workers' rights, selling garden chemicals and animal testing on those chemicals were all criticised.
Brown said: "The poor ratings for Dobbies, Tesco and Wyevale are because they are owned by companies you would not necessarily associate with the garden centre itself. There's a disparity between the policies of Dobbies and Tesco for instance. We rate on the parent company but take into account strides taken by the company in question.
"Tesco has a good record on CSR (corporate social responsibility) according to its website but Dobbies has no supply-chain policy of its own, so scores worse than Tesco on this.
"Areas that haven't received much attention in garden centres are animal testing and supply chain. All centres sell garden chemicals that have been tested on animals but none have a credible animal-testing policy in place. We want to flag up the issue to the sector as it was to the cosmetics industry decades ago.
"Garden centres sell products that have been quarried in very harsh conditions overseas and garden furniture also has sweat-shop labour issues, as has been highlighted in the clothing industry.
"We tried to be positive where there are positives. This is a sector that has made leaps and bounds in recent years but we don't want to paint a false rosy picture."
Dobbies chief executive James Barnes said: "The score allocated to Dobbies by Ethical Consumer magazine is apparently a joint Dobbies/Tesco score, a fact not made clear by the publication when it approached Dobbies for information, or in print to its readers. Both Tesco and Dobbies have excellent records on corporate responsibility and entirely reject these findings.
"Speaking for Dobbies, we are extremely disappointed by the score allocated. We do not feel this is an accurate or true reflection of our company's position and our developments in the field of corporate responsibility.
"We have made very significant and extremely innovative strides in improving our environmental credentials over the past four years and have invested substantial sums of money in doing so."
A Wyevale representative said: "We don't understand the methodology they have used. We don't think it is rigorous. It is a shame they know absolutely nothing about the business and the way it is structured.
"The scoring seemed to be driven by a wider set of issues that are not relevant to us, such as animal testing, where we got a black mark for having no policy. The whole thing seems opaque."
- Dobbies 0/20
- Wyevale 5/20
- Focus 7/20
- Homebase 7.5/20
- B&Q 8.5/20
- Notcutts 9/20
- Klondyke Strikes 10/20
- Squire's 10/20
- Wickes 10.5/20