Most of us have fallen into this common trap.  There is that great big garden to fill up and looking at that large empty void, it’s really hard to believe that those diminutive plants from the nursery are ever going to fill in so that our garden will look as lush as the ones we’ve been drooling over in the gardening magazines.  As we shop for perennials, the vision of those luxurious borders packed with plants keeps popping into our heads and when we find a plant that is described as a vigorous grower--we jump on it thinking that we will reach our ideal garden that much faster.  

            Well, that philosophy works for a while, but unfortunately, garden thugs don’t quit spreading just because they have filled up their allotted space.  When invasives have outgrown their own spot, they begin a systematic attack on their neighbors’ territory and before you know it, your whole garden has surrendered to the invader.   

My sandy loam offers so little resistance to aggressive rhizomes—almost any plant has the potential to spread too far.  Some of the more notable invasives were ‘Silver King’ artemisia that sent runners everywhere in what seemed to be only days, sundrops (Oenothera fruiticosa) that still pop up in my garden even though I yanked it out years ago, and a giant Miscanthus that a misguided friend gave me (she claims she warned me).  This monster tunneled under twenty feet of plastic and rock before I discovered it trying to make a break for the lawn. 

            Some of the worst invasive plants have even escaped from gardens to become pernicious weeds in the wild. A notorious example here in Minnesota is purple loosestrife (Lythrum salicaria, L. virgatum), which has already succeeded in eradicating acres of the native vegetation that provides shelter for waterfowl and other wildlife. Although varieties such as ‘Robert’ or ‘Morden Pink,’ are self-sterile, many experts now believe that these hybrids can cross with others of the species creating new hybrids that are not sterile. As a result, it is now against Minnesota law to have lythrum growing anywhere in your yard or garden.  The photo on the left was taken near my home where loosestrife has almost taken over the local wetlands.

            The easiest way to avoid problems with invasive plants is not to plant them in the first place. So how can you avoid planting a potentially invasive plant? 

1. I hate to be a cynic, but I have found that the most invasive plants in my garden almost always came from well-intentioned friends.  Whenever someone offers you a division from her or his garden, always ask if it is an aggressive spreader.  Chances are the reason they have it to offer is they have had to dig out large chunks because it has spread like wildfire in their own garden.

2. Read between the lines when you are buying plants from catalogs.  When you see “vigorous” translate that into invasive and if a plant is described as a “good ground cover” you can usually make the same leap.

3. If it has lysimachia in its botanical name—it is usually invasive.  The same holds true for most mints and their relatives (monarda and physostegia).

4. Check my list of invasive plants at the end of this article.  All of these plants have proven to be rampant spreaders in my own or friends’ gardens.  I still grow many of those that I have included on this list; however, now they are all together in one garden where they can “fight it out!”

 HERBACEOUS PERENNIALS THAT CAN BECOME INVASIVE

Achillea millefolium, yarrow
Aegopodium podagraria, goutweed, snow-on-the- mountain
Allium tuberosum, garlic chives
Artemisia ludoviciana, ‘Silver King & Queen’
Campanula rapunculoides, rover bellflower
Convallaria majalis, lily-of-the-valley
Helianthus tuberosus, Jerusalem artichoke
Hemerocallis fulva, tawny (common orange or "ditch") daylily
Leucanthemum vulgare, oxeye daisy
Leymus arenarius, Lyme grass
Lysimachia, most species
Lythrum, loosestrife
Macleaya cordata, plume poppy
Mentha, mint
Miscanthus, non-hybridized species, silver grass
Monarda cultivars, bee balm
Oenothera fruiticosa, common sundrops
Phalaris arundinacea, ribbon grass
Physalis alkekengi, Chinese lantern plant
Physostegia virginiana, obedient flower
Sedum, acre & kamtschaticum, stonecrop
Solidago, goldenrod
Spartina pectinata, cordgrass
Tanacetum vulgare, tansy
Tradescantia virginiana, spiderwort

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