What makes a plant invasive? The first lesson in what NOT to plant

The majority of my time (and therefore the bulk of what my clients paid me) in various gardens in which I worked was spent removing invasive plants. As a matter of fact, the removal, control, and eradication of invasive plants are a huge expense for many communities, states, and the federal government.

Who pays these bills? Taxpayers do.

This means that a large amount of our tax dollars is being spent trying to control invasive species. In the United States, the estimated cost of controlling invasive species is $138 billion per year, introduced plants cost approximately $23.4 billion in annual crop losses, and invasive species now occupy more than 100 million acres and are spreading at the rate of 3 million acres every year.

There are many beautiful native alternatives to invasive plants. Please check with your local native plant society for suggestion of native plants appropriate for your area.

Many of these out-of-control plants have been introduced by the horticultural trade

Many of these out-of-control plants have been introduced by the horticultural trade for use in our gardens. Our desire to be unique, to possess something new, has created a vast market for the importation of exotic species.

Some of these plants have been used in gardens for more than 100 years prior to them escaping from our gardens, becoming invasive, and consuming our wild places.

The fact that some of these species have been in cultivation in our gardens for so many years before they escaped and became invasive makes the importation of more and more exotic species a scary concept.

How do we know which plant will be named the next noxious pest? Do you want to be responsible for the next invasion?

Most Hated Plants

Some of these plants have become very familiar to most of us: Oriental Bittersweet (Celastrus orbiculatus), Purple Loosestrife (Lythrum salicaria), kudzu (Peuraria montana), Porcelainberry (Ampelopsis brevipedunculata) and multiflora rose (Rosa multiflora).

I’ve begun cataloging some of the worst offenders in the “most hated plants” ongoing feature.

If you live in southern Florida you are probably aware of Melaleuca which is spreading aggressively throughout the everglades, wreaking havoc on native plant and wildlife communities.

If you live in any of the western states, you have spent large amounts of time picking the sharp seed spikes of cheatgrass (Bromus tectorum) from your clothing. Cheatgrass was imported from Eurasia as a promising forage plant in drylands for cattle but has now spread invasively across most of the continental U. S. and causes additional problems because it can increase the intensity of fires.

It is very important that you contact your local county extension office or do a Google search (example “invasive plants in Pennsylvania”) to obtain a list of invasive plants in your area.

Never purchase or plant any species from this list in your garden. Carry this list with you every time you shop for plants. If the plant you are considering is on this list DO NOT PURCHASE IT!

Some plant breeders are attempting to create hybrids of some of these plants which they claim are sterile and therefore are unable to reproduce and cause environmental harm. For example, a “sterile” form of purple loosestrife has been developed, but scientists have shown that these cultivars do produce fertile seeds when they are cross-pollinated by a different cultivar.

The low-down on Buddleia

It may come as a surprise to many butterfly gardeners that the number one recommended plant for attracting butterflies, Butterfly Bush (Buddleia davidii and hybrids), is considered an invasive species in many states.

I have seen this myself in West Cape May, NJ, where this species is now appearing in already fragile dune ecosystems. The mere suggestion that this plant should be avoided has been the cause of many people becoming quite upset with me.

How can I possibly say not to use a plant that every book about butterfly gardening and every gardening guru says is the best plant to use to attract butterflies with its nectar? How can all those other people be wrong? It is my stance on the use of this particular plant that has gotten me accused of being a “native plant nazi.”

This plant has become established outside of the garden from New England and Michigan south to Georgia and on the west coast from British Columbia south through California. In Oregon, it is overtaking native plant communities along streambanks because of its dense, thicket-like growth and because it shades out native plants.

The problem with Buddleia is that it produces prodigious amounts of seeds; a single flower stalk can produce more than 40,000 seeds which are dispersed by wind and water. It is imperative if you have this plant in your garden that you deadhead all flower stalks after bloom; do not leave these in the garden or compost them after pruning, they must be thrown away or burned.

Part of the reason that I have such strong feelings about this plant is that no matter how much it is stressed to gardeners that this plant must be deadheaded, very few people actually carry out this task. If we really must have this plant in our gardens, we must each take responsibility for preventing its spread. If you cannot commit to deadheading, then this plant should not be in your garden.

Taking Responsibility for Our Own Actions

Because so many plants that are now considered invasive have been introduced by the horticultural trade, it is up to each of us to take responsibility for keeping these plants out of our little corner of the planet.

It is our responsibility to discover which plants are invasive in our state and not perpetuate their spread by purchasing them for our gardens.

It may be helpful to educate the owners of the local garden center that these plants are causing extreme ecological and economic damage and encourage them to discontinue the sale of any invasive plants. They may or may not be responsive to this, but we can only hope that with enough education of all involved parties that we can slow the spread of these plants.

It is my fondest wish that all nurseries, and especially Home Depot and Lowes (because of their enormous market share) would decide to do the right thing and discontinue the sale of any invasive plant!