The company also confirmed that Marcel Willems has left. Willems was at Mahood Brothers, which Glendale bought in 2014.
Bennett was managing director at Merediths, which Glendale bought in 2013.
Glendale Horticulture also owns Coblands Nurseries in Kent.
Glendale's parent company Alston Investments published its annual accounts recently, with Glendale Horticulture having revenues of £8.4m and a loss before tax of £355,000.
Bennett was at Four Oaks trade show in a personal capacity after having left the business, which was exhibiting at the show, late last month.