Ajuga reptans as an invasive weed
Taking a walk through a wealthy neighborhood is interesting, both from an anthropological and botanical point of view. The manicured lawns, symptoms of a deep-seated cultural neurosis, and regularly refreshed bark mulch around alien cultivars of plants that imply the regular presence of paid landscapers and herbicide. These neighborhoods also encourage a very different community of weeds, including many feral ornamental landscape plants.
This includes the curious patches of purple I kept seeing on peoples lawns. On further investigation it turned out to be one of these feral ornamentals, bugleweed.
Ajuga reptans is native to Europe, Western Asia, and parts of Northern Africa and is commonly found in woodlands, meadows, and along the edges of forests. It does particularly well in moist soils high in organic matter and provides excellent forage for pollinators. It is vigorous and quite attractive, with dark foliage and lovely blue spikes of flowers. This has made it a natural choice in landscaping, with many cultivars developed for a variety of landscape uses.
It has taken to captivity with enthusiasm, adapting to new environments to the point of escaping cultivation and becoming a weed. The Invasive Plant Atlas of the United States reports sightings of the plant across the US, with the most problematic behavior seeming to manifest in the wetter parts of the eastern and southern United States. It has managed to gain footholds in western Washington state, however, which is concerning for a variety of reasons.
A Mediterranean climate presents unique challenges for a plant like bugleweed. The summer is basically rain-free, meaning there is very little chance it will spread into non-irrigated areas, particularly those that receive decent sun. Seedlings would struggle to survive their first season and plant fragments would dry before they were able to take root. The fact that they are able to survive in Utah, Washington, and Oregon is not a great sign.
Of course, none of this applies to coastal, heavily forested, and riparian habitat where it seems likely Ajuga might be able to very easily gain a foothold regardless of climate regime. It does well even in soils that flood seasonally, waterlogged soil, and out in the open in moister coastal environments. It can spread very easily through vegetative or sexual means when the conditions are right and is challenging to completely remove.
So should we plant bugleweed?
If you are in an area that gets summer rain, probably not. I understand the utility of the plant – it is used as an herb (without much scientific backing) and is (kind of) edible, bees seem to enjoy it, and it is beautiful. It has enough invasive potential that planting it near forests or next to riparian areas is extremely dangerous to native ecosystems.
That being said, this isn’t Vinca. It suffers in drought, so those of us on the west coast might not need to worry as much provided we maintain the plant responsibly. I do not endorse planting it, but if you are going to plant bugleweed, keep it well-enclosed and far away from natural areas where it might be able to spread and keep a close eye on it if it is able to spread beyond your property.