This week’s weed is one that is, thankfully, unlikely to be recognised by most Opotiki readers as it is not common in our district. However, I have found a small number of plants so be on the lookout for it. It was introduced to New Zealand from Central or South America and was first recorded as spreading into the wild in 1946.
Cathedral bells (Cobaea scandens) was cultivated as an ornamental garden plant and ornamental it certainly is. Its dramatic, purple flowers, borne on long stalks, may be 5cm across. Each flower is bell shaped (the cup) and has a large pale calyx (the saucer) at its base. Young flowers emit a rather unpleasant odour in the evenings. At this time of year many large oval seed pods are being produced which explode to release round winged seed.
Cathedral bells climbs over other plants by means of very fine twining tendrils and grows up to 12m a year. It is this habit that makes it so undesirable in the wild as it can rapidly smother native vegetation. It also grows prolifically from seed. Cathedral bells is considered a serious enough invasive weed that it is classified as a progressive control pest plant in Environment Bay of Plenty’s Regional Pest Management Strategy. Land occupiers are required to dispose of any cathedral bells plants growing on their property.
If you think you have cathedral bells in your garden, let me know and I may be able to assist with its removal. The best treatment is to cut it down and treat the stem bases with a strong glyphosate solution: one part glyphosate to five parts of water. The numerous seedlings will need to be pulled out during subsequent years.