Like most gardeners, my garden is composed of some plants that I inherited when I bought my home, others that I bought before I really knew much about plants and still others that I purchased in my ongoing efforts to create a wildlife garden.
And like many native plant lovers, my garden is a mix of native and non-native plants. In my mind, that’s a good thing. Personally, I’m not a native plant purist, I don’t think a typical residential garden should be designed exclusively with native plants. I can certainly appreciate that point of view, but from both my perspective as a regular gardener and also as a professional garden designer, I feel that limits the available plant palette way too much.
There’s no magic ratio of native to non-native plants that will work for every gardener, we each need to find our ideal native plant planting pyramid that works best for us and our wildlife garden. Every garden should be viewed as a work in progress, and finding that ideal mix of native and non-native plants is part of the fun of creating a wildlife garden.
From Well-Mannered to Garden Thug
The problem with some of those inherited and bought-before-I-realized-the-importance-of-my-garden plants is that they can be potentially invasive. Let’s face it, it can take years, even decades, for plants that gardeners know are a problem to be officially declared as invasive. So a plant may currently not be officially listed on your state’s invasive plant list, but it can still be showing invasive tendencies in your area and can be crowding out beneficial native plants.
To my dismay, I’ve been finding that some of the plants I purchased years ago, when I was simply creating a garden – not a wildlife-friendly garden or a native plant garden or a garden with lots of biodiversity, just a pretty garden – are becoming invasive.
Way back when, I bought about a dozen Japanese spirea (Spiraea japonica and Spiraea x bumalda) and planted them in various areas of my garden. Truth be told, for about 10 – 15 years, they were ideal garden plants. They weren’t fussy about soil, water or light conditions. They were deer-resistant, low-maintenance, flowered reliably and some even had colorful foliage. I considered Japanese spireas to be one of those plant-and-forget shrubs that many gardeners are looking for.
But a few years ago, I started noticing a problem. The Japanese spireas were reseeding. At first, it was just a few seedlings here and there that were easy enough to pull out during routine weeding.
But this summer, the number of spirea seedlings has multiplied dramatically. This pretty little innocent-looking flower
Was quickly becoming this spent flower head with hundreds and hundreds of seeds
Which were turning into hundreds of little Japanese spirea seedlings
After a little research, I found that all the cultivars I planted are on this list of invasive cultivars of Japanese spirea. If only I knew then what I know now!
Here in Connecticut, neither Spiraea japonica nor Spirea x bumalda is listed on the Connecticut Invasive Plant list. But my experience with excessive reseeding is not unique. Nor is Japanese spirea the only such potential garden thug that masquerades as a well-behaved garden plant. Maiden grass (Miscanthus sinensis) and butterfly bush (Buddelia davidii) are two other widely available species that are showing invasive tendencies in the state.
If you find yourself with a potentially invasive plant in your garden, there are several steps you can take to mitigate any possible issues.
Educate yourself. Admittedly, this can be difficult because, regardless of a plant’s tendency towards invasive behavior, if it’s not officially listed on your state’s list of invasive and noxious plants, it might be for sale in your local garden center and more than likely is available for sale online. Keep in mind that just because a plant is for sale doesn’t mean you should buy it and bring it home.
In addition to checking with your local Cooperative Extension or master gardener’s office about the thug-potential of plants, you can start paying attention to what’s invasive in nearby states. The Center for Invasive Species and Ecosystem Health, the Invasive Plant Atlas and the Plant Conservation Alliance are just a few reliable resources.
While Japanese spirea is not listed as invasive in Connecticut, it is considered invasive in many mid-Atlantic states, a definite warning sign. So, when you’re reading your favorite glossy gardening magazine, check out the list of invasive plants and look for potential red flags.
Banish the bullies. Ideally, any potentially invasive plants should be removed from your garden. But let’s face it, that’s not always an immediate option.
Be Responsible. When it comes to my Japanese spirea, unfortunately, removal of all twelve shrubs is not going to happen right now. So I’ve decided to prune them to try to prevent the flowers from going to seed. Controlling seed dispersal through pruning, mowing or weeding can be time-consuming but it’s a good option until you can get rid of any potentially invasive plants.
Use Mulch. Many potentially invasive plants, like Japanese spirea, thrive in areas where the soil has been disturbed. Seeds often lay dormant in the soil for years and once brought to the surface through some type of nearby disturbance, they germinate. The benefits of organic mulch that is applied in a layer several inch thick are numerous, including reducing seed germination.
Native Alternatives to Japanese Spirea
The good news is that there are many native alternatives to the garden thugs that may be considered invasive in the near future.
A few of my favorites to plant instead of Japanese spirea are arrowwood viburnum (Viburnum dentatum), blueberry (Vaccinium corymbosum), smooth hydrangea (Hydrangea arborescens), summersweet (Clethra alnifolia) and Virginia sweetspire (Itea virginica).
Are you finding previously well-behaved plants becoming more aggressive in your garden, too? What are you doing to control them?
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