Hunter's purchase of 315,783 shares at 1,845p a share brought his holding in AIM-listed Dobbies to 25.57 per cent.
Last week, Tesco unveiled a£15-a-share recommended cash offer for Dobbies, valuing the retailer at£155.6 million. The grocer intends to extend Dobbies' product offer into a wider range of environmental lines and appeal to emerging green consumers.
The pounce was widely seen as a threat to Hunter, who has led consolidation in the gardening retail sector after acquiring market leader Wyevale last year.
Broker Seymour Pierce said Hunter is 'in a position to block Tesco's offer, irrespective of what it may increase to'.