Wednesday, the Atlanta Botanical Garden will break ground on a public garden on 165 rolling Gainesville acres that were donated in 2002 by Lessie Smithgall and her husband Charles, the late media magnate.

During the decade it took for the project to reach this milestone, a period in which the Atlanta garden completed two expansions of its own and managed through the recession, plans for the northeast Georgia project have evolved and expanded, including more than doubling seating capacity for an amphitheater. The first phase will open next year.

Now it is being positioned as an important cultural addition to growing Hall County, roughly an hour north of Atlanta, not just a woodsy satellite of the Midtown attraction.

What was originally announced as Smithgall Aboretum has morphed into Smithgall Woodland Garden, a suggestion of the broadening notion of it as more than just a haven of hardwoods and mountain laurels. Among other changes, plans for an 800-seat amphitheater have grown into one with a capacity of 2,000 — big enough to lure some of the major music acts that appear at the Atlanta garden every summer.

“I felt like ‘aboretum’ was a tough word to sell to the public,” said Atlanta Botanical Garden President and CEO Mary Pat Matheson, who arrived in Atlanta not long after the Gainesville project was announced. “They don’t understand it. It’s not sexy.”

Plus, Matheson wanted the new green spot to feature not just towering trees but also gardens boasting native Piedmont flowers and plants beneath and around them. The plan even came to include an “enchanted” children’s garden that was added after the project was announced. Featuring a steam-breathing dragon whose gaping mouth kids will be able to walk into, the children’s garden will come in the second phase of Smithgall Woodland Garden.

But first things first. The $21 million initial phase, targeted for a summer 2014 opening, will comprise a winding, wooded entry road, a visitor center, 5 acres of display gardens and the amphitheater.

Beyond the children’s garden, the second phase will include a native plant conservation nursery and a student training and education center. Its budget and completion date are still to be determined.

A 5,000-square-foot greenhouse has operated on the property just off U.S. 129/Cleveland Highway since 2004, as has a 3-acre conservation nursery. Neither has been open to the public, however, so Smithgall Woodland Garden has existed as something of a secret, even in the Gainesville area, until now.

“It’s a great market,” Matheson said. “I think in a few years this garden will be the largest cultural institution in the community — (in terms of) the size of the garden and the programs that we will do.”

She also expects the garden to draw North Carolina-bound travelers off I-985. For those already members of Atlanta Botanical Garden, admission will be free.