Is Buddleja Butterfly Towers invasive?

Question

I bought a couple of young Buddleja Butterfly Towers "Magenta" plants a couple of months ago. They are happily growing away in my garden.

I have recently stumbled upon this article that describes buddleja butterfly bushes as worse than Japanese knotweed.

I did a lot of searching to find out whether all varieties of buddleja are invasive. Some are and some aren't. I found that the dwarf ones are not invasive.

I didn't find anything about the invasiveness of buddleja butterfly tower. Does anyone know? The shrub is widely available on websites such as Thompson & Morgan in the UK.

Answer 1

With regard to the UK, this quote is from the Royal Horticultural Society:

Known as the butterfly bush, the fragrant flowers of buddleja are a favourite nectar source for butterflies. These undemanding, mainly deciduous shrubs, deserve a place in every garden with their spectacular displays of blooms and honey scent.

No mention of the plant being invasive.

Here is the RHS list of invasive non-native plants covered by the EU Regulation on Invasive Alien Species (which still applies to the UK). Again, no mention of buddleja. There's a lot of scaremongering associated with so-called "invasive" plants. Not surprising really, as frightening house owners provides a living for businesses who eradicate those plants (the second link provided by @Jurp being an example).

I had a Buddleja davidii in my garden (20 miles north of London) for several years. I got rid of it not because it was invasive, but because it was too big for the available space (even after cutting it hard back each spring). Walking the local streets I can see no evidence that my ex-buddleja has self-seeded and taken over the neighbourhood.

My advice is not to believe everything you read in The Sun and enjoy your buddlejas.

Answer 2

I agree with Peter's answer; if you look at the images in the Sun, they demonstrate a complete lack of attention and neglect in earlier years. In my experience, yes, Buddleia does sometimes (though not often) produce seedlings which would get weeded out with all the other weeds and germinated tree seedlings; I always deadhead them as soon as the flowers fade, which helps to reduce seedlings. In fact, I find having a relatively mature Acer in the area more of a problem - those air plane seeds blow all over the place, and I end up pulling out masses of seedlings from it the following spring. Unless you intend to leave your entire garden untouched for the next ten years, any seedlings that pop up can easily be removed. On neglected or wild land, yes, Buddleia can be a big issue, but not so much in a reasonably well tended garden.

Answer 3

If you do a web search on "invasive buddleja" you will find loads of sites describing the plant as invasive (it's not invasive in my area of the world (yet) because it tends to die after one winter).

Here's a somewhat hysterical article from the US and one more pertinent to your location in the UK. Whether a cultivar is dwarf or not is irrelevant to whether they'll spread seeds far and wide - what matters is sterility. ANd this means total sterility, not reduced sterility or reduced fertility. As this site explains, even a cultivar rated to produce only 2% viable seeds can produce up to 60,000 viable seeds in a season.

Here's an excerpt from that site:

In 2019, the Ticino Society of Natural Sciences in Switzerland reviewed the available research on these [reduced fertility] B. davidii cultivars to assess how environmentally safe they are.

The Ticino Society review raised serious questions about how “environmentally safe” B. davidii cultivars are. It concluded that:

• Reduced fertility is still fertility
• Cultivated reduced-fertile or sterile cultivars can cross with invasive individuals found nearby in the wild;
• Gene transfer from reduced-fertile or no-seed cultivars can modify wild individuals and, conversely,
• Gene transfer from fertile wild individuals can modify reduced-fertile or no-seed cultivars;
• Sterile plants can revert to fertile plants in time (by gene transfer or spontaneously) (Marazzi, B., & De Micheli, 2019).

So yes, it looks like all buddleia cultivars are invasive in the UK and everywhere else outside of their native range in Asia.