The awards recognises Lord Howick's work in establishing a collection of 11,000 trees and shrubs from 1,800 taxa and planted in six geographical groupings at Howick arboretum.
Howick Hall and its gardens have gone from strength to strength since the opening of the nearby Alnwick Castle gardens in 2001. Howick now attracts more than 30,000 visitors a year.
"We were getting 7,000 to 8,000 a year but once Alnwick got underway and there were a quarter of a million people coming to the area, we realised we could get some of them to come here," says Lord Howick. "So we put in a tea room and proper loos and started to advertise. It has gone from there."
Lord Howick's reaction on winning the VMH was one of pleasant surprise. "It is always nice to be given a pat on the back," says the former banker, whose City career included a directorship until 1982 of Baring Brothers & Co. "It's obviously a very nice compliment and it makes me feel rather pleased, but a lot of other people have put an awful lot of work into the whole project."
Planting began at the 65ha arboretum shortly after Lord Howick returned to the family home in 1982, following 20 years in London.
"The old garden had always been here and I was attracted by doing something surrounding it, which was following on from a naturalistic garden and doing it traditionally. It was all planted from seed but we were then able to exchange seeds and seedlings."
The first specimens in the ground came from a North American expedition in 1985. They included red and scarlet oaks and a tulip tree, which did not survive the Northumbrian conditions.
The site now has alders and birches approaching heights of 12m, although not everything has grown so fast. The Japanese umbrella pine has barely reached 1.8m about 15 years after it was planted. Lord Howick says: "Up here, I regard growing slowly as an important factor and I prefer it that way."
He is particularly fond of his Wingnut plants from China and Japan (part of the walnut family Juglandaceae). Eastern Asia has been a happy hunting ground for him; many of his expeditions, usually joining horticulturists from major botanic gardens, have proved fruitful.
"I particularly enjoy going to China and Japan; it always feels very exotic. China especially has an enormously rich flora. It is interesting to see what can and what cannot be grown."
More recent finds include Correa calycina and Xanthocyparis vietnamensis from Vietnam, a new genus that is closely related to Cupressus.
"Every other year people send out a list of what they have got," Lord Howick explains. "It's like small boys swapping stamps – it's tremendous fun. You can go and get trees from other arboreta but you have to decide what you are trying to do and you can bend nature so much but you are limited by what will grow well on the east coast of Northumbria.
"We have advantages in good soil and shelter but we have found by trial and error what grows. The most irritating ones won't grow well but won't die."
Though the future looks bright for the arboretum there are many unanswered questions. There is room for expansion, with at least 16ha of unplanted land around the arboretum, but such plans require careful consideration.
"The problem is that we've always thought about 40,000 (visitors) would be our limit and if we want to expand beyond that (we) need to build big infrastructure. We have always sold the place as completely uncommercial and we try to keep it as natural as possible. It is one of our main strategies."
Keeping the site natural is part of a wider conservation plan, although Lord Howick quips that climate change could be very helpful for growers up north.
Joking aside, he says the issue needs to be addressed urgently and small projects have an important part to play.
"What we are doing in the way of preserving things is really pretty minimal – if you look at what others are doing, we are another little piece in that jigsaw. I would describe us as a small piece in the large jigsaw of in situ conservation, and I belong to that school of thought that says in situ is more important."
1969-82: Director, Baring Brothers & Co
1973-82: Council member, Friends of the Tate Gallery
1973-85: Trustee and executive committee member, National Art Collection Fund
1982 to date: Manager of estate, Howick Hall
1987-2001: Non-executive director, Northern Rock Building Society; Trusteeships Lovaine Trust (Syon Park Arboretum); Chelsea Physic Garden; Kemerton Conservation Trust; The Botanics Foundation, Edinburgh; Royal Botanic Garden Edinburgh
Advisory roles: Member of advisory council, Westonbirt and Bedgebury arboreta.