Kings Seeds intended to donate 50p to services charity Help for Heroes from each packet of Poppy Victoria Cross that it sold.
The firm lost 18 employees during World War One and had 18 benches commissioned, bearing the employees' names, that it placed between Coggeshall and Kelvedon in Essex.
Kings Seeds said it was "fitting" to support Help For Heroes to recognise and support the men and women of the armed forces still fighting in wars today to mark the centenary of the start of World War One in 1914 and the 70th anniversary of the D-Day landings in 1944.
However, company representative Claire Hart added: "Kings Seeds has been told that despite their wish to raise funds for services charities - be that Help For Heroes and/or the Royal British Legion - they are not able to do so by selling poppy seeds because the Royal British Legion has a sponsorship relationship with B&Q, hence it has expressly advised Kings that they cannot do so, even anonymously.
"This is extremely disappointing for Kings Seeds, who only wanted to follow in their founders' benevolent footsteps and support worthwhile causes."
She added: "Because the poppy is the Royal British Legion's own emblem, they won't let us donate. We will donate behind the scenes if necessary without flagging it up to the paying public."
Help for Heroes press officer Richard Miles said: "The poppy is the symbol of the Royal British Legion and their annual poppy appeal. So the public isn't confused between donations to Help for Heroes and the Royal British Legion, we aren't able to accept money from the sale of poppy-related products. We direct those wishing to make donations using a poppy symbol to contact the Royal British Legion."
A Royal British Legion representative added: "We cannot take any donations from them because we have an exclusive deal with B&Q for the next 12 months.
"Kings cannot donate anonymously to the Royal British Legion because of our partnership with B&Q. It would be unusual for a poppy to be used to raise money for another charity."
"We are delighted to be partnering with the Royal British Legion for the next 12 months, selling poppy seeds in store to raise money for the centenary poppy campaign that remembers and pays respect to those who gave so much during World War One."