William Sinclair warned investors that the shortage will lead to a fall
"The performance in the year ending 30 September 2012 has been badly affected by unprecedented weather conditions and is not a reflection of the long term prospects of the business," the company said in a statement.
Chief executive Bernard Burns will step down as of early 2013 but will retain responsibility for the resolution of a complex compensation claim for the halting of harvesting at a now protected bog area at Chat Moss in Lancashire.
The horticultural supplier made a pre-tax profit of £3.2m pounds in 2011, on revenues of £54.3m.
The company owns about 810 hectares of peat bogs in England and Scotland.
Bord na Mona has revealed it has harvested only 37 per cent of what it expected this year.