There is a mass freeze happening at the Natural History Museum. Three million plants from the Museum’s important botany collection are being frozen to make sure they stay free of pests.
This is before they move into their new home in the state-of-the-art Darwin Centre cocoon building, opening this autumn.
The 40-tonne Maersk freezers being used have one of the highest cooling capacities of any container
Each of the plant specimens goes through a 1-week freezing cycle in giant 40-tonne Maersk freezers. They were brought in especially for the massive task and have one of the highest cooling capacities of any container.
Once in the freezer, the temperature is taken down to a chilly minus 30°C and held there for 3 days. It is then raised slowly back to normal temperature. This process kills pests and their eggs without damaging the specimens themselves.
Staff are one third of the way through the continuous packing and unpacking process and they will continue until the end of the year before it is completed.
This historic plant specimen was collected on Captain Cook's first voyage
Many of the specimens in the Museum’s botany collection are very valuable and historic, for example the Banksia integrifolia plant collected by Sir Joseph Banks and Daniel Solander at Australia's Botany Bay in the 17th century on Captain Cook's first voyage.
The curators who look after the specimens have a constant battle trying to protect specimens from deterioration.
They are at risk from biological threats, such as carpet beetles, biscuit beetles and vodka beetles; environmental threats such as the wrong temperature, humidity, light and air quality; and physical threats such as mechanical damage from handling.
The move to the new cocoon building will reduce all of these risks. The cocoon has been designed to be as insect-proof as possible.
Big-cone pine, one of the 3 million botany specimens moving into the new Darwin Centre
It has 3.3km of purpose-built steel cabinets that have tightly sealed doors and minimum inaccessible areas where dust can collect.
There are few windows and the air temperature is held at 17°C with the stable relative humidity kept at 45%.
Two groups of plants will be left out of the freezing process, the ferns and lichens. They are not attractive to pests as they tend to be tough, unpalatable and contain toxic tannins, so they won’t be moving to the new Darwin Centre.
Lithocarpus ‘Stone Oak'
Flowering plants at the Museum were previously arranged by the Bentham and Hooker Genera Plantarum system where plants were classified based on their morphological features.
In recent years, however, the development of molecular systematics has resulted in a new classification of flowering plants based on DNA analysis. This is known as the Andiosperm Phylogeny Group or APG classification.
With the move to the new Darwin Centre, the scientists now have the ideal opportunity to update the arrangement of the flowering plant collection to reflect this new system.