To prevent possums from damaging the garden, install fencing around the garden, or place wire cages around individual plants, and eliminate food sources and nesting sites on the property. Installing an electric fence around the affected area, removing other food sources and installing hardware cloth over potential nest entrances also effectively prevents possum damage.
If the possums are nesting on the property, apply 1/4-inch hardware cloth to the nest entrance several hours after dusk. Bury the hardware cloth 6 inches into the soil to prevent the animals from digging under it to enter the nest. Keep pet food stored indoors, and stop feeding birds for several weeks, or use a spill-proof bird feeder to further encourage the pests to move.
If fencing the garden isn't practical or possible, trap the possum using a live trap, and release the animals according to local regulations. Humane methods of killing possums include using a carbon dioxide chamber or shooting the animal. In gardens where possums aren't well-established, set up a motion-sensor-controlled sprinkler near the affected plants to scare the animals away from the area.
For long-term possum control, apply a product to the lawn to eliminate grubs in the soil, as grubs are one of the possum's main food sources.