I had a great conversation with a volunteer last week on the topic of exotic, invasive species growing in one’s yard. What sparked the little chat was an observation the garden volunteer made about seeing some purple loosestrife growing in someone’s yard, and “isn’t that awful”? My response was, “well, that depends”. I tend to get an itch when anyone has strong knee jerk reactions to anything on either side of a debate, especially around the topic of invasive species versus natives, as I have expressed in other blog entries. In my not so humble opinion, one needs to keep one’s head and use their their botany/ecology mind when considering such topics.
I had a similar conversation with a former intern of mine while working for Cleveland Botanical Gardens. She pointed to a clump of Arundo donax (giant reed grass), and asked why I was growing an “invasive” species. It was news to me, so I did a little investigating and thinking (i.e. no knee jerking). I discovered Arundo is considered invasive in certain settings and conditions, but what I wanted to know was its means of reproducing/spreading (i.e. seed dispersal). It turns out this species is pretty sterile and spreads almost exclusively via vegetative growth. The conditions under which it was invasive? Wetlands. My plot of land had no contiguous connection to any wetland location and was easily kept in check by my shovel. With no viable seed able to jump ship, my giant reed grass was an island. As a public institution, one could argue I was sending a wrong message, “If they can grow, so can I.” However, I felt the plant’s use as a great hideaway for children in a children’s garden and educational talking point (i.e. this is a grass! Can you believe it? We get reeds for musical instruments from it) outweighed any possible confused messaging.
When making planting and land care decisions, one must use their mind and the best data science can provide, and this is what I shared with this garden volunteer. The key to whether a person’s garden is an island or not, when it comes to invasive plants, is its means of spreading (i.e. seed dispersal, etc). This requires a little digging and thinking. One cannot naively assume their property is so far from the “wild” that they can safely plant, for example, burning bush (Euonymus alata, which spreads via birds eating berries). Birds can travel long distances before they deposit seeds. Your garden is not ultimately an island for most things as we are all interconnected, but in what ways? It is these interdependent relationships a responsible gardener needs to think carefully through.
Josh Steffen, Horticulture and Facilities Manager
Great Article, Thanks for sharing.
Please keep them coming
I appreciate the level-headed, researched approach. But Josh, what is the case that Purple Loosestrife will not be a problem at Wellfield? You addressed Arundo and burning bush, but not Lythrum salicaria. In my limited reading it looks like it is a huge problem for degrading wetland habitat.
John, thanks for the follow up. I was wondering if anyone would notice I left the original question hanging. The answer is also: it depends. From the USDA link I provide in the article body, it is not exactly clear how seed is dispersed. Loosestrife, with its small seeds, can be spread via the wind to a limited extent. It is also thought to disperse via water as well. Birds may also possibly ingest or carry it in plumage and move seed as well. Animal fur can offer another means of transportation. With so many means of dispersal, high seed production and germination rate (over 90% in yr old seed), I would not recommend planting loosestrife anywhere. There are just too many ways for it to escape your yard. We are constantly pulling it out at Wellfield, and we can attest to its ability to spread. Hope that helps. -Josh
In our region pampas grass is outlawed. This includes the aggressively invasive Cortaderia jubata, as well as the reasonably well behaved Cortaderia selloana. However, some ‘sterile’ cultivars are still available. The problem is that some sterile cultivars are only sterile because they lack male flowers. They can still contribute to the naturalization of more papas grass if they hybridize with Cortaderia jubata. In the big picture, they do not contribute much. If there Cortaderia jubata is already in the area, a few other pampas grass will not make much difference. Nonetheless, we do not plant them in suburban areas. However, in the middle of Los Angeles and San Jose, there is no place in the immediate surroundings for pampas grass to escape to.
Thanks for sharing that, Tony, we’re thrilled that Josh’s blog has led to thoughtful discussion – – and as you indicate, the challenges of invasive species goes far beyond our ‘local’ backyards, but across North America. We must all be more thoughtful in ALL of our planting/landscaping endeavors.
I do not get out much, but it seems that everywhere I go, there are invasive exotic species. I think that there are more here than anywhere I have ever been because of the mild climate, but I really do not know. The Pacific Northwest has it pretty bad too.
Sure does seem scary when so many invasives have become naturalized and many people do not even recognize them as invasive and destructive to our native habitats.
In California, treehuggers actually want to protect them!!