What Are Environmental Weeds & How To Use Them
An environmental weed is a plant that is capable of invading, out-competing and preventing the regeneration of native vegetation.
These once well-loved plants are now on the ‘not wanted’ list in our gardens.
- Bitou bush (Chrysanthemoides monilifera), a yellow-flowering shrub with a spreading habit, is out of control in some coastal sand dunes.
- Cotoneaster is an evergreen, thornless, pest- and disease-free screening shrub with the bonus of red autumn to winter berries. However, this shrub is now spreading to bushland.
- Crocosmia (Crocosmia x crocosmiiflora), above, also called montbretia, is an easy-growing corm that naturalises in gardens. Loved for its carefree orange, yellow and red flowers that bloom in summer, it is now an invasive weed.
- Another weed is Dutchman’s pipe (Aristolochia macrophylla), a flowering climber related to native species. It attracts an endangered butterfly, the Richmond birdwing, but fails to provide food for the caterpillars.
- Gloriosa lily (Gloriosa superba), a herbaceous climber, has red and green trumpet flowers. It has invaded coastal areas in the tropics and subtropics. However, large- flowered named varieties, such as ‘Rothschildiana’, are not considered a problem.
- Gorse bush (Ulex europaeus) is a major weed in New Zealand. A yellow-flowering shrub with spiny leaves, it provides cover for rabbits and prevents stock from grazing.
- Ivy (Hedera helix) was once hailed as an ornamental solution to difficult, dry-shade areas but it can cause structural damage to buildings. It supports itself by means of aerial roots and once it gets into a tree, it can kill it. Ivy can also cause allergies.
- Lantana used to be popular as a drought-hardy shrub, but it is now regarded as invasive and is known to be poisonous to stock.
- Pampas grass (Cortaderia species) was a used as a garden accessory to the Spanish-mission style of architecture, which was popular in the 20th century, but it spread into bushland and coastal areas and is now considered a weed.
- Privet (Ligustrum species) was once popular as a tough, evergreen hedge for city gardens. Its berries are attractive to birds, which spread them into bushland. The perfume from its flowers can cause allergies.
- Trident maple (Acer negundo) is an easy-to-grow shade tree. Its seeds spread so easily it is now growing in areas where it’s not wanted.
- Willow (Salix species) was once considered a useful tree for damp spots. However, many species grow readily from broken branches and supplant native vegetation along water courses.