The institute, based in Tulse Hill, has been awarded the grant for its 'Plant recording for all ages' project, which will bring the herbarium up to date, make it accessible to all and enable visitors to use it for a range of activities. The project will start in May 2016 and will take two years.
The herbarium at the institute contains around 100,000 pressed plant specimens, some of them 200 years old. They are all housed in the original cabinets designed by institute founder Allan Hume over 100 years ago.
Conserving these fragile specimens and installing digital interpretation facilities so that visitors can view them online will be central aims of the project. The institute will also widen its range of already popular educational activities for school children, adults and young people to complement the refurbishments.
Stuart Hobley, head of HLF London, said: "Rare flowers, strange fungus, not to mention thistles and moss... the historic plant collections of the South London Botanical Institute are home to fascinating examples of our botanic heritage.
"Many of these are beautiful, extraordinary and intriguing but also very fragile. Thanks to lottery players, our grant will use digital technology to help many more people access and enjoy these remarkable plant specimens."
Marlowe Russell, SLBI trustee, said: "We are delighted to have received further support from the Heritage Lottery Fund. We have already made huge developments at the institute using their last grant and are looking forward to updating our herbarium so that visitors have even more to enjoy and learn about when they come here."
The SLBI was founded in 1910 by Allan Octavian Hume, a dedicated social reformer, with the aim of bringing botany to the working people of south London. This aim continues today, with people from local communities and further afield able to explore the plant world, enjoy the botanic garden and library and participate in a wide range of activities.