History of the Gardens

The Mercer Legacy

In 1949, Thelma and Charles Mercer purchased a 14.5-acre tract of natural land along Spring Creek in Humble, Harris County, Texas.

Initially, Thelma Mercer was someone who, in her own words, “didn’t know one plant from another” but soon became an accomplished horticulturist spending much of her time digging flower beds, planting and potting plants, which over the next 24 years, became a garden paradise.

Husband, Charles Mercer, a Lt. Colonel (Ret.) was a decorated soldier and recognized engineer. Together, they began to selectively clear this “wild, wooded, burned-out area” to make room for trees such as dogwoods, parsley hawthorns, rusty black-haw viburnums and several species of hawthorns.

Thelma also planted large camellias that are still seen throughout the central garden and introduced several exotic tree species that are still growing beautifully, including gingko and bauhina. Over those twenty-four years, Mrs. Mercer planted numerous plant specimens that now form an impressive collection.

Charles’ abilities as an engineer were utilized on many projects.  One such project remains a favorite place at Mercer for photographers and children, known as “Thelma’s Pond,” a small pond with koi and large goldfish. When Thelma commented that she would like to have a pond, Charles had her layout the design with a garden hose, he then dug and constructed it. It became a joint endeavor as he did the concrete work and Thelma laid the bricks along the edge.

In 1973 Charles retired and the Mercers made the difficult decision to relocate to the Rio Grande Valley. Rather than see their beloved paradise in which they had invested so much labor and love be bulldozed by commercial developers, they wrote to Harris County Precinct 4 officials recommending that the county purchase the site.  Although the Mercers were not wealthy, they offered the property to Harris County Precinct 4 at a price far below its market value with a stipulation that it would grow and be maintained as a garden and horticultural education facility serving the people of Harris County, providing them the joy and tranquility it had given them. And, so it has.


“The idea of bulldozers coming in here and destroying the work of nature that we had tried to preserve and learn about and learn to love and enjoy is hard to take.”

—Thelma Mercer in a letter to Harris County in 1973

After Harris County purchased the gardens, a group of community gardeners interested in furthering the development of Mercer as a botanical facility formed the nonprofit group Mercer Arboretum Advisory Committee (MAAC). In 2000, the organization changed its name to The Mercer Society (TMS) with the purpose of assisting the Gardens by organizing and implementing activities that encourage membership support, expand community awareness and raise funds in support of Mercer’s strategic plan.

Much has changed at Mercer since Charles and Thelma labored together to clear trees and plant their garden, but one thing that has not changed is that Thelma and Charles Mercer’s vision become reality. Thelma’s personal desk where she wrote that letter offering their paradise to Harris County resides in the Visitor Center while her “spirit” as garden advisor lives on at Mercer.

This nationally recognized now 300-acre horticultural treasure now showcases the Gulf Coast region’s largest collection of natives and cultivated plants. Each year more than 250,000 visitors, including thousands of children, explore the beauty of the Gardens while learning how important plants are to the sustainability of the environment and the community’s quality of life.

-originally published in the Spring 2012 Issue of ParkScapes.