The Maze Runner Wiki
"They're the ones who take care of all the heavy stuff for the Gardens. Trenching and whatnot."
Zart to Thomas in The Maze Runner

Track-hoes do the hard work around the plants. Zart, who is the Keeper of the Track-hoes, mentions trenching as part of their job. Since their work is not regularly required, they also do other works in the Glade during off times.

Gardeners are similar to Track-hoes who take care of the plants in the Gardens: weeding, pruning, planting seeds, and harvesting veggies are examples of the things they do. On his second full day, Thomas works in the Gardens with Zart, who answers many of his questions.

Since these jobs are of minor importance to the development of the story they are scarcely mentioned and tend to get mixed up. In the movie, both jobs are not distinguished at all.