The chickweed seller would have earned his keep by gathering plants and weeds from the countryside to sell in the town. These plants might be for wealthier people to feed their pet birds on, or for posies to give to loved ones. Another name used to describe people like this was 'Botany Ben'.
The chickweed seller has collected groundsel, ivy, forget-me-nots and ferns. Ferns were often pressed and used in people's decorative collections.
Work such as this was often regarded as 'the lowest of the low', but Ford Madox Brown regarded the chickweed seller as having a place next to the navvies: he has not been taught to work, but is keeping himself busy and earning money, rather than turning to crime.