The first event will be the Southern Connection Congress, to be hosted by the University of Otago's botany department on January 21-25.
This will be followed by the fifth Global Botanic Gardens Congress, to be held at the Forsyth Barr Stadium from October 21-25.
At the same time, Botanical Gardens Australia and New Zealand (BGANZ) will hold its two-yearly conference.
Dunedin City Council botanic garden team leader Alan Matchett, who successfully presented Dunedin's bid to host the global congress, said the events would attract hundreds of participants.
Dunedin's botanic garden is the oldest in the country - 10 days older than that of Christchurch, he said.
Announcing the dates during a recent visit to the Dunedin Botanic Garden, world-renowned botanist and conservationist Emeritus Prof Peter Raven, of Missouri Botanical Garden, said the congress would have an emphasis on plants in southern lands and their conservation.
The convention was also an opportunity to monitor progress on the 16 targets of the global strategy for plant conservation.
These include increasing information about plants, developing plans to manage species that threaten plants, ensuring no wild flora is endangered by international trade, sustainable use of plants, and increasing the number of people trained in plant conservation.
Prof Raven, who during his visit gave the John Smaillie Tennant Lecture to more than 400 people in Dunedin, is keen for people to do what they can for conservation rather than become overwhelmed by the enormity of the problem.
He advocates such things as recycling, using less energy, using cars less and generally living more conservatively - "there can be a lot of pleasure in that".
To those people who might question whether it was important to save plants, Prof Raven said plants, collectively, supported everyone.
They provided food, medicines and materials for building and clothing.
Their potential was still not known.
"I would turn that question on its head. Why shouldn't we save as many as we can?"
He likened the situation to sitting on a plane, watching someone out the window pulling out rivets on the aircraft one by one.
That person might have pulled out only one or two, but "pretty soon the wing falls off. The problem is, we don't know at what point the wing will fall off."
Prof Raven would like to see more students study plants. Such study had been lagging behind the study of animals and micro-organisms in recent years.
He said a well-functioning university botany department, such as that at Otago, was very powerful in fostering that interest.
Otago is the only New Zealand university with a botany department.
Deputy department head Prof Katharine Dickinson said there were jobs "out there now which can't be filled because there are not enough people who know plants".
Prof Raven said parents could help develop their children's interest in the environment by giving them opportunities to learn about the world they were in through such things as visits to botanic gardens and wild areas near where they lived.
During the visit to the garden, Prof Raven and his wife, Dr Pat Raven, were delighted by the antics of a fantail, which they initially thought was a bird not native to New Zealand called a wagtail.
Botanical meetings
• Southern Connection Congress: Jan 21-25, 2013
• Global Botanic Gardens Congress: Oct 21-25, 2013
• Botanical Gardens Australia and New Zealand: Oct 21-25, 2013
