The Seed Freedom Rotorua event is being held as part of worldwide protests across six continents to assert the rights of people to collect and save their own seeds rather than allow multi-global corporations to control the supply of all seeds.
Ms La Grouw said saving seeds was something people had done for generations. She said it was important people continued to do that and ensured the survival of different crops.
Ms La Grouw said there was no scientific proof genetically modified crops were safe, or decreased the need for the use of pesticides.
Seed Freedom spokesman Alan Solomon said action would continue with petitions to regional and district councils after Saturday's event.
He said if pending legislation was passed to allow widespread introduction of genetically-modified crops, there could be huge implications on Rotorua's tourist economy and agricultural and horticultural industry.
Mr Solomon said at the moment New Zealand was one of the only countries not to allow genetically-modified crops to be grown outside controlled environments.
The pair hope the current moratorium on growing GM crops will be extended another 10 years. Similar events are being held in Auckland, Dunedin, Hamilton, Thames and Wellington.