What does it look like?
Nasturtium is a rambling or trailing, hairless, aromatic plant that grows as an annual or short‑lived perennial. It often spreads along the ground but can climb up to two metres high. The plant has soft, succulent stems containing watery sap that can grow up to 10 metres long.
Its distinctive leaves are round and shield‑shaped, about 18 - 21 centimetres across. They are sometimes slightly uneven in shape, bluish underneath, and attached to the stem by a long stalk at the centre of the leaf. Flowers are tubular and can be scarlet, orange, or yellow. They appear from October to May and may grow singly or in clusters. Each flower is about four centimetres across and has five uneven petals.
After flowering, nasturtium produces soft, green, three‑sided seed capsules containing caper‑like seeds.
Nasturtium matures quickly and produces many viable seeds, smothering habitat. It tolerates salt, wind, hot to cold, semi-shade, damp, damage, and poor soil.
Why is it a problem?
Due to its smothering nature, it prevents the establishment of native plant seedlings. Nasturtium spreads by soil movement, dumped vegetation, scrambling stems and possibly birds and browsing mammals.
It’s likely to invade disturbed sites, especially adjacent to gardens and dumps, shrublands, herb fields, wetlands, and stream sides.
Control methods
Physical control
It’s easy to control - pull up all vegetation (all year round). Dispose of at a refuse transfer station or burn or bury deeply.
Herbicide control
Spray (spring-summer) using glyphosate (10ml/L + penetrant). Check for resprouting stem and follow up six monthly. Replant sites densely to lower the light levels.
CAUTION: When using any herbicide or pesticide, PLEASE READ THE LABEL THOROUGHLY to ensure that all instructions and safety requirements are followed.
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