The move followed a review of supply-chain costs and reflected increasingly challenging markets, the Chester-based firm said.
Fertiliser markets had become more "volatile" while logistics costs had gone up, said sales manager Richard Huxtable.
"It also reflects our increasing focus on efficient ammonium nitrate and granular NPK production at our Ince and Billingham facilities," he added.
The company employs 600 staff on the two major sites in Britain, which produce 1.6 million tonnes of products to supply a total market of 4 million tonnes.
Huxtable said: "This move is regrettable, but following the closing of supply options from Denmark and Belgium it has been difficult to meet the needs of Irish markets."
GrowHow employs two business managers across Ireland and is talking to them on their future roles in the company or redundancy.
Marketing manager Ken Bowler said the firm had been "scaling down" for "a couple of years".