Tucked away behind the Victorian Palm House at Kew Gardens in west London, a quiet allotment has been coming back to life with the arrival of spring and the help of one of its volunteers.

Kit Connor, 21, looks up at the oldest potted plant in the world, a 250-year-old cycad that threatens to shatter the ceiling of the Kew Gardens Palm House. Lush, green, and stretching over 330 ...