We can see why Bob likes the Pickerel Weed (Pontederia cordata) growing by the side of the dam. It’s hardy and has glossy green leaves and spikes of attractive blue flowers that emerge in summer. They’re quite stunning and for now look lovely. This is why they have been commonly cultivated as an ornamental plant in garden features around the country.
The problem is that they have been naturalized and are now spread throughout slow moving waterways and wetlands of Australia. Once established in native areas, seeds can be spread downstream during heavy rain or floods. It is currently classified as an emerging threat and has the capacity to develop into dense clumps in natural wetlands and waterways, replacing native species and restricting water movement. On the southern coast of NSW it has been declared a noxious weed. They cover the surface and reduce light levels, temperature and oxygen in the water below, affecting the communities of native plants and animals. In addition they eventually interfere with water access, reduce water quality overall and block water pumps.
Whilst these plants are still small, they can be manually removed and will do little harm. However if they grow larger herbicides will be necessary and on a Conservation property we like to limit their use, if at all. Especially in or near our dams, they have a devastating effect on the wonderful ecosystem already established and reflected in a health population of frogs and aquatic animals.
I hope that in reading this that Bob will remove these plants from his dam. We are constantly learning about what is good and bad for the environment and it is sometimes hard to make a decision about what will be best in the long run, especially when they are hardy, grow well and there are flowers involved.
In a contained water garden they are a beautiful addition, they provide nectar for bees and butterflies and are a habitat for frogs and the flowers bloom throughout the summer. Perhaps a solution would be for Bob to plant them in a pot by the dam to contain them.
They are an edible plant and do have uses. The seed of the Pickeral Rush is nutritious and starchy and can be dried or eaten straight from the plant, apparently tasting like puffed rice. They can also be dried, boiled, roasted or even ground into flour. I must learn more about grinding seeds as this is also the case with the Bunya nut. The young leaf stalks can also be cooked or eaten raw in salads (I wonder if the bunnies would like them).
If you were to grow this plant in a contained aquatic environment, they can be planted in 20cm water depth, in a shallow container in full sun. Use 10 cm of heavy soil and top with 10 cm of gravel mulch. The only thing you would need to do would be to continually divide the plant as it grows prolifically. The flower stems can grow up to 1.2m tall.