At the most basic level (and somewhat unscientifically) - a weed is a plant growing where it’s not wanted. A plant can become a weed because of the way it grows, the way it reproduces and the way it impact on its surroundings. In some case these weeds can cause problems for our environment, our economy, our way of life, or our cultural values.
As you read more about weeds on other sites and sources, you’ll see that there are a heap of terms used to describe specific subgroups of weeds, and it can get confusing. Hopefully this will help a bit.
Plants that have always been in New Zealand, or have evolved from plants that have always been here, are described as native or indigenous. Plants which are only found in New Zealand are called endemic.
Plants that have been introduced in New Zealand from other countries are sometimes described as alien or exotic species.
A naturalised plant is one that has been introduced to New Zealand from elsewhere and can now grow and spread on its own without help from humans. Not all plants introduced from foreign places are able to naturalise, and not all naturalised plants are a problem.
When we want to emphasise the seriousness of a weed’s spread, we often describe it as invasive. This means it has the potential to invade the places that are special to New Zealand.
Some weeds are a problem in lots of different situations. Others become a problem for one type of land use but not for others. Agricultural weeds are a problem for farmers. Horticultural weeds are a problem for growers.
Garden weeds or nuisance weeds are a problem to gardeners in their own gardens. If they ‘jump the fence’ from gardens and become a problem in New Zealand’s natural areas, we call them environmental weeds.
When weed problems are being highlighted in specific ecosystems, you might hear them referred to as wetland weeds, dune weeds, coastal weeds, or perhaps riparian weeds.
Weeds don’t only occur on land. There are also aquatic weeds that cause problems in freshwater systems, and marine weeds that invade our coastline and coastal waters.
Pest plants are weeds that have legal status and rules for management under a Regional Pest Management Plan. Not all weeds are declared pest plants – sometimes weeds don’t make it into the regional plans because they are too widespread (or not widespread enough) to meet the criteria that councils use - but that doesn’t mean they aren’t a problem!
Pest plants are sometimes called plant pests, which can be confusing as this term is also used for insects and diseases that threaten non-weeds that we want to keep growing.
Plant pests are sometimes called noxious weeds, but you won’t hear that term used much now – unless you are talking to old timers who remember how things were on the farm ‘back in the day’!