A notice posted by Southwark Council at the garden entrance says: "Constant anti-social behaviour and the on-going presence of vermin has forced us to remove much of the undergrowth and cut back the shrubs in this area."
"In the future we hope to implement measures which will encourage wildlife, but deter anti-social activities.
"We apologise for any inconvenience caused."
In March this year Southwark Police Cadets collected 20 used needles and syringes during a weapons sweep in the nature garden.
The wildlife area was established just over a decade ago with funding from the then Borough & Bankside Community Council in memory of murdered local teenager David Idowu.
The garden features a mosaic-covered memorial bench to David Idowu unveiled in 2011.