New Zealand has some rules on materials and stuff you can’t bring into the country at all. This includes any and all living organisms such as house plants (they wouldn’t survive the boat trip in the dark for 3 months anyway), but also seeds, parts of endangered species, anything with honey or made by bees, Christmas ornaments with natural elements such as pine cones and moss and a whole lot more. More information on this can be found here on the official website of the New Zealand Government. On the New Zealand customs website you can also find more information about what is prohibited and what needs declaring. We’ve found that the rules for shipping our items by sea and what we brought on the airplane are the same.
Identify all this stuff and either give it away or throw it away if there is no use for it anymore, like plant seeds past the expiration date. We rehomed almost all of our plants with friends and family and threw out old Christmas decorations that might not pass inspection.