Cognitive decline is not inevitable with advancing age. It’s common knowledge that various lifestyle factors – regular exercise, adequate sleep, mental stimulation, a positive outlook and a healthy social network – contribute to healthy brain ageing. Many people instinctively feel that time spent in nature, amongst plants, should be added to this list of preventative factors. This makes perfect sense according to the Biophilia hypothesis, which proposes that humans have a genetically determined affinity with the natural world and are more likely to thrive when connected to nature.

The Japanese have a particular term for spending time in nature that recognises its therapeutic benefits. ‘Shinrin-yoku’ means ‘forest-bathing’ and it’s at the core of preventative healthcare in Japanese medicine. The premise is simple: visit a natural area and walk in a relaxed way and there will be calming, rejuvenating and restorative benefits. The idea of nature as therapy is not unique to Japan, however.

Therapeutic horticulture encapsulates the process of using plants and gardening to promote, improve and preserve well-being of mind, body and spirit. It is a bourgeoning field of practice both in Australia and internationally.”

In October, the Australian Therapeutic Landscapes Conference will take place on the Gold Coast and presentations will address the use of plants and gardening to meet a range of needs such as mental health and perinatal care and social inclusivity for dementia patients.

Sensory gardens are often used for therapeutic purposes, with the potential to stimulate memory and cognition through sound, touch, taste, smell and sight. Aromatic plants are an especially potent trigger for nostalgia, memory and emotion. For me, the sweet scent of rondeletia never fails to evoke thoughts of playing in the front garden of my first childhood home, while frangipani perfume always transports me to my university days and those sultry, airless Brisbane evenings before the strike of a summer storm.

Undoubtedly, just being amongst plants will do positive things for your brain. Benefits may also be reaped from ingesting particular plants known for their cognition-boosting properties. Ashwagandha (Withania somnifera), a member of the nightshade (Solanaceae) family,  is an example of a herb prized for its neuroprotective qualities. Researchers at Newcastle University in the UK have found that ashwagandha inhibits the formation of beta-amyloid plaques. These plaques, considered toxic to brain cells, accumulate in the brains of people with neurodegenerative diseases, such as Alzheimer’s. (The studies were conducted in test tubes so the researchers emphasise that more testing is needed before people turn to ashwagandha as a reliable remedy for diseases of the brain).

In what could be good news for some elderly folk, a 2017 study published in Nature Medicine and carried out by researchers from the University of Bonn and the The Hebrew University of Jerusalem suggests that cannabis is another plant that may improve cognition in humans of an advanced age. In the study, low doses of tetrahydrocannabinol (aka THC  – the chemical responsible for most of marijuana’s psychological effects) were given to ageing mice before subjecting them to a series of cognitive tasks. The mice that had received the THC performed on par with much younger mice in their prime. But before you rush out to light one up in the name of dementia prevention, it’s worth noting that when THC was given to young mice the opposite effect was observed – the younger mice’s cognition was impaired and they performed worse on the tasks. What a cruel paradox.

My two grandmothers (one of whom is no longer alive) are women whose physical health outlasted their cognitive clarity. It’s sobering, and sad, to bear witness to the deterioration of a mind, especially that of someone you hold dear. It also serves as a reminder of the impermanence of something we take as a given while we’re young. I could adopt a defeatist attitude towards diseases like dementia and Alzheimer’s when there is a history of these conditions in my family. Maybe my brain’s future is already foretold. But it seems to me that causative and preventative factors are not so clear-cut when it comes to maintaining a healthy mind, and plants could be but one piece of the complicated puzzle.

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