Maryland Grows

When it comes to landscaping, a huge decision-making point is what we find visually pleasing… and often what pleases us visually ends up being something we are not very used to seeing, meaning that we pick plants that seem more exotic to us so we can marvel at their surprising (to us) beauty. This is all good and nice, but the problem appears when we realize that many of those plants appear exotic to us because they are exotic to the region we live in! This means that if we select them to plant in our landscapes, we are actually adding to our environment species that are not necessarily native to where we live… which can have pretty drastic consequences. In today’s post, I want to talk about a potential solution that has fairly recently been proposed to the use of such plants: sterile varieties.

What’s the deal with exotic plants?

Although not all exotic plants will have negative effects on our environment, some of them do. Those that do are considered invasive species, and they can create a lot of trouble in our local ecosystems. Invasive plants tend to grow faster than other native plants, often overrunning the spaces they grow in, spreading very quickly, and eventually “choking” or outcompeting local species, which end up dying out and/or becoming unable to survive in the presence of the invasive plant. Some good examples of this behavior of invasive plants in Maryland are the Chinese and Japanese Wisteria vines and the English Ivy, all of which effectively cover trees and can eventually choke and pull them down to their death.

In Maryland, this issue has been recognized not just by ecologists, but also by lawmakers, who have started to regulate the selling of specific species to properly support the protection (and recovery) of our local plant communities. Among the most recent additions to these regulations are the ban on selling several bamboo species, English Ivy, exotic Wisterias, and several very invasive grasses (among other species). You can check the most up-to-date list of these species at the Maryland Dept. of Ag. website: Maryland Prohibited Invasive Plant Law and Regulations. The Maryland Department of Natural Resources also hosts a website with a lot of information about exotic species (plants and others): Invasive and Exotic Species in Maryland

So what to do if we love the plants but do not want them to spread?

Ideally, if we do not want to harm local habitats, the best decision is to refrain from planting invasive species, because they are REALLY hard to properly control and prevent their spread (especially when there is bird-mediated fruit dispersal or stolon-mediated dispersal).

An alternative, however, is the selection of varieties that are unable to spread because they are sterile or do not have proper structures to do so. These are varieties that exist for some ornamentals/exotics, and that are in some cases exempted from the regulations that I was mentioning above. Some examples are non-invasive bamboo varieties, some Berberis cultivars (e.g., varieties “Lemon Glow”, “Crimson Cutie”), and even some almost-sterile Buddleja cultivars (e.g., “Flutterby”, “Lo and Behold” varieties developed by several University programs). A note on some of these cultivars is that although some of them are labeled “sterile”, they may or may not be fully sterile. Some of them have indeed been shown to, in some cases, produce some fertile offspring (although way fewer than their fertile counterparts!).

How to go about these decisions?

Generally, when considering exotic ornamentals for our green spaces, it is worth making it a practice of first informing ourselves about their potential for invasiveness. Then, if the potential is there, another good practice is to look for potential alternatives (e.g., do we really need to plant that specific plant?, are there less-harmful varieties?, are there native alternatives that can be planted instead?, can we properly contain the plant if it spreads?).

To make these decisions, a good tool to consider is the NC Extension Gardener toolkit, where species and varieties are listed and can be filtered out by (among other traits) their potential for invasiveness/weediness. The Maryland Invasive Species Council has also put together a list of species that have invasiveness potential (independently of regulations) and are thus of concern. A new tool from the University of Maryland Extension Maryland Native Plants Project can help you search and filter for native plants, so you can potentially choose a native plant which will suit your needs and benefit our eco-system: Maryland Native Plant Finder tool.

By Anahí Espíndola, Associate Professor, Department of Entomology, University of Maryland, College Park. See more posts by Anahí.

Anahí also writes an Extension Blog in Spanish! Check it out here, extensionesp.umd.edu, and please share and spread the word to your Spanish-speaking friends and colleagues in Maryland. ¡Bienvenidos a Extensión en Español!