Joyner, 51, rented out land near his home at Cockwells Nursery, Harbertonford, Totnes, Devon to two men who used it to store a huge 130,000 tons of wood, earth and building waste. A fire broke out on 16 May 2016 after he evicted them after finding out about the dumping, which he was then responsible for clearing up.
He admitted on 19 November at Exeter Crown Court keeping controlled waste between February and May 2016 in a manner which was likely to cause pollution to the environment or harm human health.
The fire has burned for three days before Public Health England ruled it was a hazard and asked the fire service to put it out.
Joyner runs Plants Galore garden centres in Newton Abbot, Exeter, and Plymouth.
He was fined £3,600 with £5,000 costs and £4,250 compensation by Recorder Mr Timothy Kenefick at Exeter Crown Court.
He said: "The fact remains that you were warned of the risk of fire if the waste was left on the site. Despite that warning, you did little to any effect to remove it or protect against the risk.
"This was reckless rather than negligent, but close to the borderline. There was a short term but substantial impact on air quality caused by smoke and ash from the fire.
"This was undoubtedly a rural area of outstanding natural beauty which was more likely to be adversely affected by a fire of this nature."