Stormy weather failed to keep the visitors away attesting to the popularity of the attraction that officially opened on February 1, 2013 and allowed the public in the next day.

The 94 forests, made up of more than 44,000 trees have steadily grown since then, as have crowd numbers.

Already generating enthusiasm from 15,000 visitors from its opening day festival, the arboretum has gone on to attract more than a million guests over its three-year lifespan.

Two of those guests were Michael and Karen Adams, who so loved the arboretum that they tied the knot above its forests on Saturday afternoon.

They are among dozens of couples to wed at the arboretum, taking advantage of the views over Canberra and the natural beauty of the attraction itself.

Leigh Taafe, the curator of the arboretum's bonsai and penjing collection, said word-of-mouth and regular revisits helped guarantee the centre's popularity.

"It does feel like a long time, however only in that we've done a lot in such a short period," he said.

"I remember vividly the opening day and how many people were here enjoying not only my collection but the collection as a whole."

The bonsai exhibit, one of the most popular parts of the arboretum, attracts about 14,000 visitors every month.

Mr Taafe said the collection had attracted many more fans since it moved from the previous site at Commonwealth Park.

"Down there on an average weekend day you might see a dozen people come through," he said.

"Up here, on the other hand, on special occasions like public holidays, weekends, Mother's or Father's Day we get upwards of 2000 people in here."

The arboretum announced former ACT chief minister Jon Stanhope as its inaugural patron on Friday.

On Tuesday, the actual anniversary of the opening, coffee, cake and branded products will be discounted, while the Arboretum magazine will be issued for free.