Thieves have broken into the Unanderra Nursery and pilfered the potted plants for the 113th time in 13 years.

Nursery owner Gwen Reid said it was not yet known how many of the dwarf lime and lemon trees had been stolen after thieves scaled a wall and broke into the property in the early hours of yesterday morning.

She said the thieves threw the plants over the property's rear fence, which backs onto the railway line.

An alarm went off at 2.30am at the neighbouring steakhouse and must have scared them away, Ms Reid said, because a number of plants were still lying by the tracks when she arrived at work yesterday.

"Everything's a mess," she said.

"All these trees have been dragged everywhere.

"We haven't been able to count how many trees are missing yet because we only just got hundreds in yesterday. They had only just arrived and these people have messed them all up and pulled them all out."

Ms Reid said despite installing barbed wire, extra fencing and infrared cameras, her business continued to be targeted by thieves.