I was attending a university-run seminar a couple of weeks ago and was rather shocked to hear the presenter mention oregano as an invasive plant in the PNW. I’ll note that the presenter was not an expert on invasive plants or even plant ecology, which is why their speaking on this topic while speaking for a large research institute surprised me. The presenter went as far as to tell the audience not to plant oregano and to remove it from their gardens.
This surprised me because I’m involved in this space of ecological gardening and invasive plants and I have never heard anything about Oregano being invasive, let alone weedy in the garden. An internet search revealed quite a few people calling the plant invasive with basically nothing to back it up.
It’s important to distinguish that invasive carries a very specific connotation. According to the Forest Service, a definition I happen to agree with, an invasive species needs to fulfill the following criteria:
An “invasive species” is defined as a species that is
Executive Order 13112
- Non-native (or alien) to the ecosystem under consideration; and,
- Whose introduction causes or is likely to cause economic or environmental harm or harm to human health.
So does Oregano qualify as invasive in the PNW, at least according to the US government?
The short answer is no. Oregano is not considered invasive anywhere in the US, and it is not on any official list of invasive species in any state. It has not been implicated in damage to any ecosystem or as causing any agricultural losses. It does not self-seed particularly easily, though in the garden it is hardy and persistent. It does not spread like mint does, however, and tends to stay in a clump.
This does not mean that oregano is completely innocent, however. It can thrive in our climate and survives fine without any additional water. This is why it has been recorded as an escapee in certain more populated areas of Oregon, though as I mentioned above it is not considered a noxious weed nor is it even considered invasive anywhere in the US, and the circumstances of those sightings is often unknown. Many of the sightings of wild oregano are decades old as well and the plant still has not become a threat in wild areas, nor does naturalized oregano seem to have become more common in general. Overall it is just not a concerning plant and probably should not be treated as much.
I think the mischaracterization of oregano as ‘invasive’ is unfortunate, as I believe that oregano is generally a very useful and beneficial plant in the garden. It needs basically no water and thrives in light shade or sun. It can handle any soil type. It is a culturally important herb that is important in many cuisines. Perhaps most interesting to me is that it is one of the plants that attract the most pollinators in my garden, in particular native long-horned bees which seem particularly fond of it. Because it flowers in the heat of summer it is often one of the most busy plants in the dry part of my garden, providing nectar during a rather hot and droughty time when many other xeriscaping flowers have gone to sleep.
There are many dangerously invasive garden plants, but I have seen no evidence oregano is one of them. I think the only precautions that need to be taken with the plant are keeping it away from natural areas, but I have never really seen it growing wild, it’s never self-seeded in my garden, and I can find little evidence of it becoming a common naturalized or invasive species in any state other than a few possible escapees near settled areas.