Speaking at Gardening Scotland, Philip said: "We've had the best May ever, beating 2004. People accept the weather killed a lot of plants. Half (of our customers) are pleased to get space back and half want to replace them."
He added that Rosemary, Bay, Phormium, Ceoanthus, Cordyline and Pittosporum were among the worst hit, with container-grown plants especially vulnerable.
Philip explained: "Scotland has been hit hard but the south has been hit much, much harder than they're used to. We've not had a bad winter for 10 years. People expected to lose these plants once every five years before."
He said there was a direct link between being seen on The Beechgrove Garden on TV and garden sales. Co-owner and Beechgrove presenter Lesley Watson added: "People are going to garden centres from the show and buying."
John Frater, Miles Nelson, Maxine Cadzow, Inglis Thorburn, Karen McCullough and Pei-Ying Chou designed Avant-Gardens this year.