Josh Egan-Wyer included the feature - a rope covered in wine and sugar to attract adult moths - as part of his insect-friendly garden.
The BSc horticulture student was one of six BSc and HND students to go before judges.
A tree forms a focal point with herbaceous plants, herbs, grasses and annuals to attract pollinating insects. "Nectar bars" include herbs and a camomile lawn while pollinator screens of old paperbacks and egg boxes will make good insect dens.
Judge and garden design tutor Tony Davy said the garden was eye-catching and educational. Egan-Wyer said he looked forward to following through the design with building his creation.