More than 90 of the former Wyevale Garden Centres are opening on 4 April for an "exclusive open day" for its 892,000 garden club members.
The Sunday Trading Act 1994 does not allow shops over 280sq m to trade, with fines of up to £50,000 per shop. GCG said its restaurants will be open and staff will run planting demonstrations, though tills will only be open to buy food and drink.
GCG chief executive Nicholas Marshall said: "With this poor spring we must try every way we can to regain sales. But we are opening to garden club members only. We won't be able to sell anything - you can sell porn but not plants on Easter Sunday - but you are allowed to run a restaurant and man the centre, so people can get advice and look at our ranges.
"We have taken advice and as long as we don't have any retail sales you're not breaking the law. You are allowed to provide a service, otherwise we would have to close hotels and restaurants and we would be a puritan country. It is a particularly silly law but that's not why we're doing this. It is an opportunity for garden club members to have a day with us."
The garden centre industry estimates losses caused by not opening on Easter Sunday at £10m. Klondyke Strikes chairman Bob Gault said the law was "a farce" that costs his company between £250,000 and £500,000 a year.
Gault owns six centres in Scotland that can open on Easter Sunday, but his 18 in England cannot. "We have been advised that it would be illegal even to open as a showroom. We'll have staff on duty at the entrances with a voucher for a free coffee on a future visit - and an apology."
HTA marketing director Andrew Maxted said: "Our understanding of the law is that even talking to customers and giving them advice is prohibited. We would be interested to see the legal advice GCG has had on this because our advice suggests this is not a route the Government is happy to see followed."
He added: "Our position on Sunday trading laws are that they are a mess and we are trying to encourage the Government to do something about that.
"As far as garden centres are concerned, there is a clear demand from the public for them to be open on Easter Sunday. Our most recent IPSOS Mori survey showed 47 per cent said they should be open and 39 per cent wanted them closed. This is a debate that has been going on for many years."
Maxted said the HTA continued to lobby on the issue but that "no meaningful" discussions are expected to take place until a new Government is formed. "We think that garden centres have a unique place in the British psyche. Garden centres are not viewed in the same way by the public as DIY stores or grocers, for instance, and we're keen to promote that," he added.
Trading Act history
Pre-1986: Sunday trading in England and Wales was not generally permitted until 1994, but garden centres, small corner shops and chemists often opened.
1986: Government failed to get Sunday trading extended. A Keep Sunday Special campaign was launched.
1994: Sunday Trading Act allowed large shops (greater than 280sq m) to open on Sundays for six hours, but Christmas Day and Easter Sunday were excluded.
2006: Government decided there was no consensus for change.