Robert Ropner, who oversaw the enterprise on the Camp Hill estate where he lives with his wife, Jo, pleaded guilty at Leeds Magistrates Court to offences under the Health and Safety at Work Act of 1974.
The prosecution was brought following an investigation by Hambleton District Council into the accident in 2017.
The groundsman was struck by a 4x4 all-terrain work vehicle which crushed him against a tree and was airlifted to James Cook University Hospital in Middlesbrough, where he spent six weeks for treatment.
An investigation by Hambleton District Council found the vehicle was in a poor state of repair, had worn brakes, and had not been subject to regular maintenance.
District Judge Holland fined the company a total of £45,000, awarded the council its full costs of more than £14,000 and imposed a victim surcharge of £190 at a sentencing hearing on Friday last week.
Paul Staines, the director of environment at the council, said: “This case was completely avoidable. The standards of health and safety at Camp Hill fell far below the standard expected for a business of this nature.
“It ultimately led to an employee being put at unacceptable risk and suffering very serious and life changing injuries. "Businesses have a legal duty to ensure work equipment is maintained in a safe condition and staff are suitably instructed or trained on the safety features of the equipment.”
Mrs Ropner, the Queen’s representative for North Yorkshire, and her husband were both directors of Camp Hill Ltd, which was based in Kirklington, to the west of Thirsk, before it went into administration earlier this year in the wake of the Covid-19 pandemic.
Mr and Mrs Ropner’s solicitor, Ridwaan Omar, said: “Guilty pleas were entered on behalf of the company and the judge noted numerous mitigating features including no previous convictions.
“This was a regrettable incident at the time involving an employee. That employee has made a fairly good recovery and went back into their employment.
“Not taking anything away from the seriousness of the incident, the level of fine reflects what the court felt.”