Wedged between the concrete jungle of Waikiki and the fenced-in wilds of the Honolulu Zoo lies a fertile patch of green and tiny ponds of golden tilapia.

The garden is an outdoor classroom that feeds the students’ appetite for learning at Jefferson Elementary School. Principal Garret Zakahi sees the vegetable beds, hydroponic and aquaponic systems, and native-plant garden as providing holistic learning in science, sustainability, cooperation, effective communication and responsibility.

“Students wanted classroom learning to be combined with real-world experiences,” Zakahi said.

The effort started in April 2015, when 20 hydroponics kits, which grow plants in a nutrient solution instead of soil, were purchased with community donations and installed on campus. Third-, fourth- and fifth-graders planted corn, kale, taro, radishes and ti. Students and parent volunteers learned how to monitor and adjust pH levels in the solution for optimal plant growth, how to add water and nutrients, and to identify sick plants.

About a month later, four aquaponics systems were installed, each containing water plants and 25 golden tilapia. These self-contained systems circulate water containing nutrient-rich fish waste to the hydroponic crops, which filter clean water back into the fish tank.

Each aquaponic system includes a 160-gallon plastic trough filled with fish. An aeration pump generates oxygen for the fish, and a separate pump and PVC pipes move water and fish waste to 3-by-8-foot grow beds filled with expandable clay.

Fifth-graders tend to the gardens along with parent and community volunteers. They’ve learned to maintain a careful balance between the number of fish in each system and the number and variety of plants.

“If the system is out of balance, you will see unhealthy plants and unhealthy fish,” Zakahi said.

Fifth-grade teacher Sarah Kim said the garden has inspired her students to undertake self-directed research and engage in problem solving.

“They’re working together. They can read about the nitrogen cycle but when they get to see it in the garden, it’s on a different level,” she said. “The hands-on learning is more meaningful to them.”

Working as a group, Kim’s students designed a fish feeder that could be used on the weekends when school is not in session.

“Gardening is fun and it makes it easier to learn than just reading books,” said Genesis Castaneda, 10. “It helps us to remember things (like how the nitrogen cycle works).”

Castaneda said the students brought home mint from the garden to make tea. And just like on a real farm, there have been failures and successes.

“Our broccoli didn’t grow but our tomatoes and basil grew good,” Castaneda said.

During a reporter’s recent visit, Christopher Kim, 11, was feeding the fish and looking for dead ones — another lesson in sustainable gardening. “We bury the dead fish to give nutrients to the plants so they will grow better,” he said. “I like taking care of the fish.”

Elephant dung from the Honolulu Zoo is used as a soil additive in raised beds that grow papaya, pineapple, kale, chard, daikon, eggplant, basil, carrots and herbs.

“Hardware Hawaii and Lowe’s donated lumber and supplies to make the beds,” Zakahi said. “The students determine what is grown.”

The garden, which has attracted visiting groups from other schools, is maintained by community volunteers during the summer months and other vacation breaks.

Jefferson students are working on a recipe book that features dishes with vegetables commonly found in their garden.

“Garden Party” spotlights Hawaii’s unique and exceptional gardens. Call 529-4808 or email features@staradvertiser.com.