Salem, the state capital, hired a herd of 75 goats to munch their way through plants like Armenian blackberry in the city's largest park.
But costs came to more than five times the city would have spent on human landscapers, a report found.
The goats also ate native plants among the invasive species, the report added.
The six-week pilot programme ended last November and there are no plans to renew it, city officials said.
Aside from their cost, the goats left behind a "heavily fertilized area", the city's public works operations manager Mark Becktel told the Statesman Journal.
The park was also said to have a "barnyard aroma" due to the goats' presence.
Oregon will not be renewing a scheme which uses goats to eat invasive species due to rising costs and complaints over the animals' odour.