I have a fondness for walking the Washburn valley. This 26km (16mile) tributary of the Wharfe lies just to the north of Otley. If you avoid the busy paths around Swinsty and Fewston reservoirs it is both peaceful and beautiful.

Sat on the grassy dam bank of Swinsty reservoir last week for a picnic lunch while out walking, I am struck by the rich variety of flowers. Recent engineering works has left the soil disturbed, and given a chance for early colonisers to germinate, grow and flower.

The most noticeable of which is Weld (Reseda luteola). This stiffly erect yellow-green plant grows up to 1.5 metres tall, thriving anywhere that has seen recent soil disturbance.

Belonging to the Mignonette family, which includes garden plants of the same name, it has a tall spike of small yellow-green flowers. Like Foxgloves it is biennial, flowering in the second year, and starts from the lower flowers moving upwards over several weeks. When the top flower buds open, the lower ones are already in fruit. This long flowering period thereby increasing the chance of pollination.

It is not native but was brought to the UK from continental Europe probably in pre-Roman times for the purpose of dyeing. Hence its alternative name of Dyers Rocket, making reference to its tall spike of flowers. Together with Woad and Madder it constitutes the most common plants used to dye cloth. All are ancient introductions, Woad a member of the cabbage family, and Madder the bedstraws.

Weld stems and leaves produce a yellow dye, Woad blue and the root of Madder red. By a process of over-dyeing, it was possible to produce all the colours of the spectrum: woad and weld for green, woad and madder for purples and browns, and weld and madder for orange. Woad as a blue dye was surpassed by indigo from India in the 16th century. With all three-natural plant-based dyes ceasing to be of commercial importance following the discovery and manufacture of cheaper synthetic aniline dyes in the late 19th century.

My encounter with Weld continued, travelling home after our Washburn walk, I stopped in Otley and investigated the waste ground next to the newly built Wharfeside care home in Westgate. It may look like a large patch of weeds to most people, but for any botanist, it is a botanical garden waiting to be explored. Yes, and you guessed it, growing and standing proud is Weld or Dyers Rocket – waiting for take-off.